N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩ Plus de détails...
An initial high fluence campaign was performed in WEST, in 2023, on the newly installed actively cooled tungsten divertor composed of ITER-grade monoblocks. The campaign consisted in the repetition of a 60 s long Deuterium L-mode pulse in attached divertor conditions, cumulating over 10000s of plasma exposure. A maximum deuterium fluence of approximately 5 ⋅ 10 26 m -2 was reached in the outer strike point region, representative of a few high performance ITER pulses. Gross tungsten erosion inferred from visible spectroscopy shows that the most eroded plasma facing component is the inner divertor target with rates ten times larger than on the outer divertor target. The outer midplane tungsten bumpers, located a few centimeters from the plasma, show gross erosion rates two times lower than at the outer divertor. We conclude that the outer midplane bumpers have a negligible contribution to the long range tungsten migration and deposition onto the lower divertor. The cumulated gross erosion rate on the inner divertor translates in an effective gross erosion thickness of about 20 μm, while it is about 2 μm for the outer divertor. Strikingly, these orderings coincide with the thickness of deposits found locally on the divertor: the exposed surfaces of high field side monoblocks are covered with several tens of μm tungsten deposits, while on the lower field side, few μm thin tungsten deposits are only found on the magnetically shadowed parts of monoblocks. The strong impact of those deposits on WEST operation, namely perturbation of surface temperature measurement with infra-red thermography, and the emission of flakes causing radiative perturbation of the confined plasma, calls for anticipating similar issues in ITER. In particular, the start of research operation shall consider the definition of a divertor erosion budget in order to anticipate the formation of deleterious deposits.
N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩ Plus de détails...
A novel sparse encoding algorithm is developed to detect and study plasma instabilities automatically. This algorithm, called Elastic Random Mode Decomposition, is applied to the Mirnov coil signals of a dataset of 1291 discharges of the TJ-II stellarator, enabling the identification of the Alfvénic activity. In the presented approach, each signal is encoded as a collection of basic waveforms called atoms, drawn from a signal’s dictionary. Then the modes are identified using clustering and correlations with other plasma signals. The performance of the proposed algorithm is dramatically increased by using elastic net regularization and taking advantage of GPU architectures, hence the signal size and the number of dictionary elements are no longer limiting factors for encoding complex signals. Once the modes are retrieved from the shots, they can be easily analyzed with standard clustering techniques, thereby describing the physical mode characteristics of this subset of TJ-II shots. The clustering features consider the relationship with the plasma current Ip, the diamagnetic energy W, and inverse squared root electronic density 1/√n, profiling different subtypes of Alfvénic activity. The proposed algorithm can potentially create large databases of labeled modes with unprecedented detail.
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩ Plus de détails...
Plasma discharges in the tungsten (W) Environment Steady-state Tokamak (WEST) are strongly impacted by W contamination. In WEST experiments, due to W contamination, the power radiated in the plasma (PRad) is on average, around 50% of the total power injected into the plasma (PTOT). Furthermore, this radiated power fraction (fRad) is almost insensitive to plasma conditions. The causes behind this experimental trend are not fully understood. In this contribution, a 3D numerical model is used to analyze the W migration in the WEST boundary plasma in different plasma scenarios. The WEST experimental database is sampled to obtain a scan of simulation input parameters. These parameters mimic the WEST plasma conditions over a chosen experimental campaign. The simulation results are compared to WEST diagnostics measurements (reflectometry, Langmuir probes, and visible spectroscopy) to verify that the simulated plasma conditions are representative of the WEST database. The W contamination trend is analysed: the W density (nW) strongly decreases when the radial distance between the separatrix and WEST antennas (Radial Outer Gap, ROG) increases. On the other hand, at a given ROG, nW increases proportionally with the power entering the scrape-off layer (PSOL). PRad is estimated with a simple 0D model. For a fixed ROG, fRad is not sensitive to plasma conditions. These trends are qualitatively and, at times, quantitatively comparable to what is observed in WEST experiments: the simulated trends are related to the poorly screened W influx caused by the erosion of the main chamber Plasma-Facing Components (PFCs). Thus, this numerical analysis suggests a possible interpretation of WEST experimental trends.
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩ Plus de détails...
This work explores the Limiter-Divertor transition (L-D) during the current ramp-up of ITER's Q=10 baseline plasma scenario at various central line-integrated density n_(li) values. The analysis, based on transport simulations performed with the latest version of SoleEdge-HDG, focuses on the time evolution of heat and ion particle fluxes, revealing regions of elevated temperature on the inner wall and plasma-facing components (PFCs) despite moderate loads.The investigation also delves into the effects of perpendicular convection flux terms on density build-up, comparing different formulations and their interplay with auxiliary heating sources. Furthermore, the paper shows the impact of taking into account the evolution of the parallel neutral momentum on plasma and neutral density at the targets in the context of an ITER steady-state scenario.
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩ Plus de détails...
Recent developments and tools integrated into the TAPaS code are presented, enabling realistic scenario simulations of particle dynamics within experimental tokamak magnetic equilibria. In particular, the enhanced capabilities of TAPaS enable seamless coupling with external simulations, provided the metric and equilibrium magnetic field of the external code are known. Coupling TAPaS with the gyro-fluid code FAR3d, the transport and losses of energetic particles in the presence Alfvén eigenmodes (AEs) in DIII-D plasma discharge #159243 were investigated. Detailed analyses of prompt losses with and without collisions were performed. Then, further analysis was performed in the presence of electromagnetic perturbations resulting from AEs activity. The results indicate that, for the energies and the initial conditions considered here, the presence of AEs enhances the particle losses.
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩ Plus de détails...
The yield stress and shear thinning properties of mucus are identified as critical for ciliary coordination and mucus transport in human airways. We use here numerical simulations to explore the hydrodynamic coupling of cilia and mucus with these two properties using the Herschel–Bulkley model, in a lattice Boltzmann solver for the fluid flow. Three mucus flow regimes, i.e. a poorly organized regime, a swirly regime, and a fully unidirectional regime, are observed and analysed by parametric studies. We systematically investigate the effects of ciliary density, interaction length, Bingham number and flow index on the mucus flow regime formation. The underlying mechanism of the regime formation is analysed in detail by examining the variation of two physical quantities (polarization and integral length) and the evolution of the flow velocity, viscosity and shear-rate fields. Mucus viscosity is found to be the dominant parameter influencing the regime formation when enhancing the yield stress and shear thinning properties. The present model is able to reproduce the solid body rotation observed in experiments (Loiseau et al. , Nat. Phys. , vol. 16, 2020, pp. 1158–1164). A more precise prediction can be achieved by incorporating non-Newtonian properties into the modelling of mucus as proposed by Gsell et al. ( Sci. Rep. , vol. 10, 2020, 8405).
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩ Plus de détails...
A steady-state, 1D semi-analytical model for prompt redeposition based on the separation between redeposition caused by the electric field in the sheath and redeposition related to gyromotion is here described. The model allows for the estimation of not only the fraction of promptly redeposited flux but also the energy and angular distribution of the non-promptly redeposited population, along with their average charge state. Thus, the temperature and mean parallel-to-B velocity of the non-promptly redeposited flux are also available. The semi-analytical model was validated against equivalent Monte Carlo simulations across a broad range of input parameters. In this paper the eroded material under exam was tungsten (W) for which the code demonstrated consistent agreement with respect to numerical results, within its defined validity limits. The model can theoretically provide a solution for any material, temperature and electron density profile in the sheath, monotonic potential drop profile, and sputtered particles energy and angular distribution at the wall. As such, this code emerges as a potential tool for addressing the boundary redeposition phenomenon in fluid impurity transport simulations.
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩
R Varennes, G Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Turbulent relaxation patterns in SOL plasma. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-04797031⟩ Plus de détails...
Abstract Relaxations of localized over-density in a plane transverse to the magnetic field are numerically investigated under the effect of drift-wave and interchange drives in SOL conditions. Such a controlled departure from thermodynamic equilibrium allows the investigation of fundamental processes at play in cross-field transport. Interchange instabilities generate ballistic outward radial flux with low amplitude zonal flow patterns, whereas drift-wave instabilities result in symmetric radial flux with large amplitude zonal flow patterns. When both instabilities are considered, the combined effects tend to favor drift-waves, leading to a weaker outward flux with larger zonal flow patterns.
R Varennes, G Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Turbulent relaxation patterns in SOL plasma. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-04797031⟩
I Kudashev, M Scotto D’abusco, A Glasser, E Serre, F Schwander, et al.. Global particle buildup simulations with gas puff scan: application to WEST discharge. Frontiers in Physics, 2024, 12, ⟨10.3389/fphy.2024.1407534⟩. ⟨hal-04703430⟩ Plus de détails...
This paper deals with the distribution of sources, transport, and exhaust of particles in a tokamak. Knowledge and understanding of all the physical phenomena involved in the global particle buildup are necessary to study and predict density regimes and subsequently to develop optimized scenarios for tokamak operation in order to control heat and particle exhaust. Neutral particles and their interactions with plasma are central in this perspective. This paper discusses the impact of varying the intensity of particle fueling in 2D transport simulations of a WEST discharge. Simulations are performed with an updated version of SOLEDGE-HDG that allows a more realistic transport of neutrals using a self-consistent diffusive model based on charge exchange and ionization processes. New code capabilities allow the entire WEST poloidal cross section to be simulated in a realistic configuration for both geometry and the range of control parameters. A gas puff scan illustrates the main features of the sheathlimited, high-recycling, and detached regimes, such as the buildup of the temperature gradient and the pressure drop in the scrape-off layer (SOL), the target temperature falling to 1 eV, and the ionization source moving away from the targets, as well as the particle flux rollover. A crude estimate of wall erosion is also provided, showing the respective role of each plasma wall component in each of these regimes.
I Kudashev, M Scotto D’abusco, A Glasser, E Serre, F Schwander, et al.. Global particle buildup simulations with gas puff scan: application to WEST discharge. Frontiers in Physics, 2024, 12, ⟨10.3389/fphy.2024.1407534⟩. ⟨hal-04703430⟩
Elena Alekseenko, A.A. Sukhinov, B. Roux. Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds. Regional Studies in Marine Science, 2024, 73, pp.103477. ⟨10.1016/j.rsma.2024.103477⟩. ⟨hal-04515082⟩ Plus de détails...
In this study, we investigate the complex dynamics of multi-fractional suspended particle transport in a shallow water basin subjected to strong wind conditions. Our research focuses on understanding the interplay between wind-induced advection and particle settlement, and its implications for sediment redistribution. Through our analysis, we reveal the distinct behaviors of different sediment fractions. Clay particles, constituting the lowest fraction in sediment cores, remain suspended throughout the simulation due to their low settlement velocity, with relatively stable concentrations. Conversely, the dominant fraction, medium silt, is suspended during intense wind events but quickly settles to the bed due to its higher settling velocity. Wind stress exceeding 0.05 Pa triggers particulate matter erosion, leading to its presence in the water column. Additionally, we explore the 2D distribution of sediment characteristics, including thickness, dry density, and mud fraction, to identify areas prone to erosion and deposition. Our findings demonstrate that coastal areas of the Taganrog Bay experienced significant erosion following strong wind events, exhibiting the thinnest sediment thickness and the highest dry bulk density. Deposition areas, characterized by thicker sediment layers and lower dry density, were often found in proximity to erosion zones, indicating the influence of particle resuspension and settlement processes. Furthermore, we analyze the implications of our findings on the vulnerability of specific regions to erosion and deposition. The central part of the sea contains moderately thicker sediment layers with a moderately high mud fraction, representing a zone of fine sediment accumulation. These fine sediments, including fine silt and clay, remain suspended for longer durations and are redistributed over greater distances by currents. Overall, our study provides valuable understanding into the multi-fractional suspended particle pathways and their interaction with strong winds in shallow water basins. The results contribute to a better understanding of sediment dynamics, which has implications for coastal management, environmental monitoring, and the preservation of benthic ecosystems.
Elena Alekseenko, A.A. Sukhinov, B. Roux. Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds. Regional Studies in Marine Science, 2024, 73, pp.103477. ⟨10.1016/j.rsma.2024.103477⟩. ⟨hal-04515082⟩
Alix Limoges, Jacques Piazzola, Christophe Yohia, Quentin Rodier, William Bruch, et al.. Study of the Atmospheric Transport of Sea-Spray Aerosols in a Coastal Zone Using a High-Resolution Model. Atmosphere, 2024, 15 (6), pp.702. ⟨10.3390/atmos15060702⟩. ⟨hal-04779475⟩ Plus de détails...
Fine-scale models for the transport of marine aerosols are of great interest for the study of micro-climates and air quality in areas of complex topography, such as in urbanized coastal areas. To this end, the MIO laboratory implemented the Meso-NH model in its LES version over the northwest Mediterranean coastal zone using a recent sea-spray source function. Simulated meteorological parameters and aerosol concentrations are compared to experimental data acquired in the Mediterranean coastal zone in spring 2008 on board the R/V Atalante. Key findings indicate that the large eddy simulation (LES) mode closely matches with the experimental data, enabling an in-depth analysis of the numerical model ability to predict variations in aerosol concentrations. These variations are influenced by different wind directions, which lead to various fetch distances typical of coastal zones.
Alix Limoges, Jacques Piazzola, Christophe Yohia, Quentin Rodier, William Bruch, et al.. Study of the Atmospheric Transport of Sea-Spray Aerosols in a Coastal Zone Using a High-Resolution Model. Atmosphere, 2024, 15 (6), pp.702. ⟨10.3390/atmos15060702⟩. ⟨hal-04779475⟩
Homam Betar, Daniele Del Sarto, A. Ghizzo, F. Brochard, David Zarzoso. A numerical study of electron-magnetohydrodynamics tearing modes in parameter ranges of experimental interest. Physics of Plasmas, 2024, 1st European Conference on Magnetic Reconnection in Plasmas, 31 (5), pp.052117. ⟨10.1063/5.0205061⟩. ⟨hal-04561813⟩ Plus de détails...
We perform a numerical study of the linear dynamics of tearing modes in slab incompressible electron- magnetohydrodynamics (EMHD) by considering some parameter ranges which can be of interest for laboratory plasmas (e.g., helicon devices) or for astrophysics (e.g., solar-wind turbulence). To this purpose several non-ideal effects are simultaneously retained (finite electron inertia, resistivity and electron viscosity) and we make distinction between the dissipation coefficients in the direction parallel and perpendicular to the guide field. We thus identify some new recon- nection regimes, characterized by a departure from the customary monotonic power-law scalings of the growth rates with respect to the non-ideal parameters. The results here presented can provide a useful indication for future studies of EMHD regimes relevant to experiments and for extensions of the EMHD tearing mode modelling to more complete regimes including kinetic effects (e.g., "electron-only" reconnection in kinetic regimes).
Homam Betar, Daniele Del Sarto, A. Ghizzo, F. Brochard, David Zarzoso. A numerical study of electron-magnetohydrodynamics tearing modes in parameter ranges of experimental interest. Physics of Plasmas, 2024, 1st European Conference on Magnetic Reconnection in Plasmas, 31 (5), pp.052117. ⟨10.1063/5.0205061⟩. ⟨hal-04561813⟩
Louis Lamérand, Didier Auroux, Philippe Ghendrih, Francesca Rapetti, Eric Serre. Inverse problem for determining free parameters of a reduced turbulent transport model for tokamak plasma. Advances in Computational Mathematics, 2024, 50 (3), pp.39. ⟨10.1007/s10444-024-10135-6⟩. ⟨hal-04569449⟩ Plus de détails...
Two-dimensional transport codes for the simulation of tokamak plasma are reduced version of full 3D fluid models where plasma turbulence has been smoothed out by averaging. One of the main issues nowadays in such reduced models is the accurate modelling of transverse transport fluxes resulting from the averaging of stresses due to fluctuations. Transverse fluxes are assumed driven by local gradients, and characterised by ad hoc diffusion coefficients (turbulent eddy viscosity), adjusted by hand in order to match numerical solutions with experimental measurements. However, these coefficients vary substantially depending on the machine used, type of experiment and even the location inside the device, reducing drastically the predictive capabilities of these codes for a new configuration. To mitigate this issue, we recently proposed an innovative path for fusion plasma simulations by adding two supplementary transport equations to the mean-flow system for turbulence characteristic variables (here the turbulent kinetic energy k and its dissipation rate ) to estimate the turbulent eddy viscosity. The remaining free parameters are more driven by the underlying transport physics and hence vary much less between machines and between locations in the plasma. In this paper, as a proof of concept, we explore, on the basis of digital twin experiments, the efficiency of the assimilation of data to fix these free parameters involved in the transverse turbulent transport models in the set of averaged equations in 2D.
Louis Lamérand, Didier Auroux, Philippe Ghendrih, Francesca Rapetti, Eric Serre. Inverse problem for determining free parameters of a reduced turbulent transport model for tokamak plasma. Advances in Computational Mathematics, 2024, 50 (3), pp.39. ⟨10.1007/s10444-024-10135-6⟩. ⟨hal-04569449⟩
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect and worse than old maintenances for a gamma degradation process. Applied Stochastic Models in Business and Industry, 2024, ENBIS 2022, 40 (3), pp.620-639. ⟨10.1002/asmb.2849⟩. ⟨hal-04462980⟩ Plus de détails...
This article considers a condition‐based maintenance for a system subject to deterioration. The deterioration is modeled by a non‐homogeneous gamma process, more precisely the gamma process and the preventive maintenance are imperfect or worse than old. The corrective maintenance actions are as good as new. The maintenance efficiency or non‐efficiency parameters as well as the deterioration parameters are considered to be unknown. The monitoring data under consideration give indirect information on the maintenance parameters. Therefore, an expected maximum algorithm is applied for parameter estimation.
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect and worse than old maintenances for a gamma degradation process. Applied Stochastic Models in Business and Industry, 2024, ENBIS 2022, 40 (3), pp.620-639. ⟨10.1002/asmb.2849⟩. ⟨hal-04462980⟩
Journal: Applied Stochastic Models in Business and Industry
Uwe Ehrenstein. Generalization to differential–algebraic equations of Lyapunov–Schmidt type reduction at Hopf bifurcations. Communications in Nonlinear Science and Numerical Simulation, 2024, 131, pp.107833. ⟨10.1016/j.cnsns.2024.107833⟩. ⟨hal-04408097⟩ Plus de détails...
The Lyapunov-Schmidt procedure, a well-known and powerful tool for the local reduction of nonlinear systems at bifurcation points or for ordinary differential equations (ODEs) at Hopf bifurcations, is extended to the context of strangeness-free differential-algebraic equations (DAEs), by generalizing the comprehensive presentation of the method for ODEs provided in the classical textbook by Golubitsky and Schaeffer [Applied mathematical sciences, {\bf 51}, Springer (1985)]. The appropriate setting in the context of DAEs at Hopf bifurcations is first detailed, introducing suitable operators and addressing the question of appropriate numerical algorithms for their construction as well. The different steps of the reduction procedure are carefully reinterpreted in the light of the DAE context and detailed formulas are provided for systematic and rational construction of the bifurcating local periodic solution, whose stability is shown, likely to the ODE context, to be predicted by the reduced equations. As an illustrative example, a classical DAE model for an electric power system is considered, exhibiting both supercritical and subcritical Hopf bifurcations, demonstrating the prediction capability of the reduced system with regard to the global dynamics.
Uwe Ehrenstein. Generalization to differential–algebraic equations of Lyapunov–Schmidt type reduction at Hopf bifurcations. Communications in Nonlinear Science and Numerical Simulation, 2024, 131, pp.107833. ⟨10.1016/j.cnsns.2024.107833⟩. ⟨hal-04408097⟩
Journal: Communications in Nonlinear Science and Numerical Simulation
Jingtao Ma, Lincheng Xu, Jérôme Jacob, Eric Serre, Pierre Sagaut. An averaged mass correction scheme for the simulation of high subsonic turbulent internal flows using a lattice Boltzmann method. Physics of Fluids, 2024, 36 (3), ⟨10.1063/5.0192360⟩. ⟨hal-04514161⟩ Plus de détails...
This paper addresses the simulation of internal high-speed turbulent compressible flows using lattice Boltzmann method (LBM) when it is coupled with the immersed boundary method for non-body-fitted meshes. The focus is made here on the mass leakage issue. The recent LBM pressure-based algorithm [Farag et al. Phys. Fluids 32, 066106 (2020)] has shown its superiority on classical density-based algorithm to simulate high-speed compressible flows. Following our previous theoretical work on incompressible flows [Xu et al. Phys. Fluids 34, 065113 (2022)], we propose an averaged mass correction technique to mitigate mass leakage when simulating high-Mach-number compressible flows. It is adapted to deal here with a density, which is decoupled from the zero-moment definition. The simulations focus on two generic but canonical configurations of more complex industrial devices, the straight channel at different angles of inclination at Mach numbers (Ma) ranging from 0.2 to 0.8, and the National Aeronautics and Space Administration Glenn S-duct at Ma = 0.6. The present results show that mass leakage can be a critical issue for the accuracy of the solution and that the proposed correction technique effectively mitigates it and leads to significant improvements in the prediction of the solution.
Jingtao Ma, Lincheng Xu, Jérôme Jacob, Eric Serre, Pierre Sagaut. An averaged mass correction scheme for the simulation of high subsonic turbulent internal flows using a lattice Boltzmann method. Physics of Fluids, 2024, 36 (3), ⟨10.1063/5.0192360⟩. ⟨hal-04514161⟩
Raffael Düll, Hugo Bufferand, Eric Serre, Guido Ciraolo, Virginia Quadri, et al.. Introducing electromagnetic effects in Soledge3X. Contributions to Plasma Physics, 2024, pp.e202300147. ⟨10.1002/ctpp.202300147⟩. ⟨hal-04474339⟩ Plus de détails...
In the pedestal region, electromagnetic effects affect the evolution of micro‐instabilities and plasma turbulence. The transport code Soledge3X developed by the CEA offers an efficient framework for turbulent 3D simulation on an electrostatic model with a fixed magnetic field. The physical accuracy of the model is improved with electromagnetic induction, driven by the local value of the parallel component of the electromagnetic vector potential , known from Ampère's law. It is solved implicitly in a coupled system with the vorticity equation on the electric potential . The consequence is a basic electromagnetic behavior in the form of shear Alfvén waves. A finite electron mass prevents unphysical speeds but requires solving for the time evolution of the parallel current density in the generalized Ohm's law. This term can be analytically included with little computational overhead in the system on and and improves its numerical condition, facilitating the iterative solving procedure. Simulations on a periodic slab case let us observe the predicted bifurcation of the wave propagation speed between the Alfvén wave and the electron thermal wave speeds for varying perpendicular wavenumbers. The first results on a circular geometry with a limiter attest to the feasibility of turbulent electromagnetic scenarios.
Raffael Düll, Hugo Bufferand, Eric Serre, Guido Ciraolo, Virginia Quadri, et al.. Introducing electromagnetic effects in Soledge3X. Contributions to Plasma Physics, 2024, pp.e202300147. ⟨10.1002/ctpp.202300147⟩. ⟨hal-04474339⟩
Frédéric Schwander, Eric Serre, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih. Global fluid simulations of edge plasma turbulence in tokamaks: a review. Computers and Fluids, 2024, 270, pp.106141. ⟨10.1016/j.compfluid.2023.106141⟩. ⟨hal-04352255⟩ Plus de détails...
With ITER, the largest tokamak ever built, and the growing number of fusion energy startups in the world, the need for numerical simulations has never been more crucial to progress towards the successful operation of fusion reactors. From fundamental plasma physics to engineering, a hierarchy of models exists from high-fidelity (gyro-)kinetic models in (5D) 6D to 0D fluid transport models. In this paper, we review the state-of-the-art of 3D turbulence fluid simulations in edge tokamak configurations. The widely used drift-reduced Braginskii equations are introduced together with the dedicated boundary conditions modelling plasma wall interactions. If until recently most of the models were focused on electrostatic turbulence driven by interchange-like instabilities, in recent years models have incorporated electromagnetic effects allowing fluctuations of the magnetic field. Specific features of the edge plasma configurations, which make these equations specially challenging to resolve and stressful for the numerical methods, are detailed. In particular, the strong anisotropy of the flow as well as the complex geometric characteristics lead to the development of dedicated discretization schemes and meshing, which are implemented in state-of-the-art codes reviewed here. It appears that the latter can be differentiated by their mesh construction as well by the manner in which they handle parallel gradients (aligned or not along the magnetic field). The review shows that no consensus on the optimal combination between meshing and discretization schemes, if it exists, has been found. Finally, examples of recent achievements show that 3D turbulence simulations of medium-sized tokamaks are currently achievable, but that ITERsize tokamaks and thermonuclear plasmas still require significant progress.
Frédéric Schwander, Eric Serre, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih. Global fluid simulations of edge plasma turbulence in tokamaks: a review. Computers and Fluids, 2024, 270, pp.106141. ⟨10.1016/j.compfluid.2023.106141⟩. ⟨hal-04352255⟩
Ivan Kudashev, Anna Medvedeva Glasser, Manuel Scotto D’abusco, Eric Serre. Impact of Variable Perpendicular Transport Coefficients in WEST Simulations Using SolEdge-HDG. IEEE Transactions on Plasma Science, 2024, pp.1-6. ⟨10.1109/tps.2024.3384031⟩. ⟨hal-04552343⟩ Plus de détails...
Plasma–wall interaction is one of the key research topics on the way to controlled fusion. To study the best operational designs with reduced heat and particle fluxes onto tokamak plasma facing components (PFCs) comprehensive plasma simulations are required. A recent implementation of a hybridized discontinuous Galerkin scheme into a new version of SolEdge code has the advantage of using magnetic equilibrium-free mesh. This allows us to conduct pioneering 2-D transport simulations of a full discharge in the WEST tokamak. In this work, we implemented plasma transport coefficients as functions of coordinate in the poloidal plane and neutral diffusion as a function of neutral mean free path. Moreover, the perpendicular convection flux terms were added to the code. Using the new features, a few test cases were investigated. The influence of nonconstant transport coefficients on the simulated particle and heat fluxes onto the WEST tokamak PFCs are demonstrated.
Ivan Kudashev, Anna Medvedeva Glasser, Manuel Scotto D’abusco, Eric Serre. Impact of Variable Perpendicular Transport Coefficients in WEST Simulations Using SolEdge-HDG. IEEE Transactions on Plasma Science, 2024, pp.1-6. ⟨10.1109/tps.2024.3384031⟩. ⟨hal-04552343⟩
L. Cappelli, J. Guterl, N. Fedorczak, D.L. Rudakov, G. Sinclair, et al.. Model validation of tungsten erosion and redeposition properties using biased tungsten samples on DiMES. Nuclear Materials and Energy, 2023, 37, pp.101551. ⟨10.1016/j.nme.2023.101551⟩. ⟨hal-04546765⟩ Plus de détails...
An experiment was performed in the DIII-D lower divertor to validate numerical SOL tungsten (W) impurity erosion and redeposition simulations against experimental data. The net and gross erosion of W were calculated as a function of the voltage (or bias) applied to the exposed material. Five samples were inserted into the DIII-D lower divertor using the Divertor Material Evaluation System (DiMES) manipulator and exposed to constant L-mode attached plasma conditions. Each sample was partially coated with W. During plasma shots, samples were biased with respect to the machine vessel ground, ranging from −60 V to 25 V. The ERO2.0 code was used to numerically simulate the experiment aiming to compare the numerical results with experimental measures. A good agreement is found between estimated and measured tungsten erosion at least for negative biases.
L. Cappelli, J. Guterl, N. Fedorczak, D.L. Rudakov, G. Sinclair, et al.. Model validation of tungsten erosion and redeposition properties using biased tungsten samples on DiMES. Nuclear Materials and Energy, 2023, 37, pp.101551. ⟨10.1016/j.nme.2023.101551⟩. ⟨hal-04546765⟩
Hassan Hachem, Hai Canh Vu, Mitra Fouladirad. Different methods for RUL prediction considering sensor degradation. Reliability Engineering and System Safety, 2023, 243, pp.109897. ⟨10.1016/j.ress.2023.109897⟩. ⟨hal-04543787⟩ Plus de détails...
Predicting the Remaining Useful Lifetime (RUL) of a system has become one of the primary goals of engineering and reliability researchers. RUL prediction is based on the measurement data collected from sensors (e.g. vibration data, temperature data). The collected data is may be inaccurate owing to sensor problems. These problems are often ignored or modeled by a Gaussian noise in most previous work. However, due to various operation circumstances and the aging impact, the sensor itself will ultimately deteriorate and its performance will deteriorate. The Gaussian noise with a constant mean is then not appropriate to fully capture the sensor degradation. In this context, this study focuses on predicting the RUL considering the sensor degradation. For this purpose, a joint model of sensor degradation and system degradation is firstly developed. In this model, the sensor degradation is modeled by Wiener and Gamma processes instead of Gaussian noise. Then, different estimation methods based on the particle filter, a popular model-based technique, were proposed to predict the RUL based on the joint degradation model. To study the performances of our methods, numerical analyzes were carried out. The obtained results confirm the performance and advantages of the proposed methods.
Hassan Hachem, Hai Canh Vu, Mitra Fouladirad. Different methods for RUL prediction considering sensor degradation. Reliability Engineering and System Safety, 2023, 243, pp.109897. ⟨10.1016/j.ress.2023.109897⟩. ⟨hal-04543787⟩
Journal: Reliability Engineering and System Safety
Jingqi Zhang, Mitra Fouladirad, Nikolaos Limnios. A Semi-Markov Model with Geometric Renewal Processes. Methodology and Computing in Applied Probability, 2023, 25 (4), pp.85. ⟨10.1007/s11009-023-10060-z⟩. ⟨hal-04543367⟩ Plus de détails...
We consider a repairable system modeled by a semi-Markov process (SMP), where we include a geometric renewal process for system degradation upon repair, and replacement strategies for non-repairable failure or upon N repairs. First Pérez-Ocón and Torres-Castro studied this system (Pérez-Ocón and Torres-Castro in Appl Stoch Model Bus Ind 18(2):157–170, 2002) and proposed availability calculation using the Laplace Transform. In our work, we consider an extended state space for up and down times separately. This allows us to leverage the standard theory for SMP to obtain all reliability related measurements such as reliability, availability (point and steady-state), mean times and rate of occurrence of failures of the system with general initial law. We proceed with a convolution algebra, which allows us to obtain final closed form formulas for the above measurements. Finally, numerical examples are given to illustrate the methodology.
Jingqi Zhang, Mitra Fouladirad, Nikolaos Limnios. A Semi-Markov Model with Geometric Renewal Processes. Methodology and Computing in Applied Probability, 2023, 25 (4), pp.85. ⟨10.1007/s11009-023-10060-z⟩. ⟨hal-04543367⟩
Journal: Methodology and Computing in Applied Probability
Alex Karagrigoriou, Ioannis Mavrogiannis, Georgia Papasotiriou, Ilia Vonta. An Exponentiality Test of Fit Based on a Tail Characterization against Heavy and Light-Tailed Alternatives. Risks, 2023, 11 (10), pp.169. ⟨10.3390/risks11100169⟩. ⟨hal-04543899⟩ Plus de détails...
Log-concavity and log-convexity play a key role in various scientific fields, especially in those where the distinction between exponential and non-exponential distributions is necessary for inferential purposes. In the present study, we introduce a testing procedure for the tail part of a distribution which can be used for the distinction between exponential and non-exponential distributions. The conspiracy and catastrophe principles are initially used to establish a characterization of (the tail part of) the exponential distribution, which is one of the main contributions of the present work, leading the way for the construction of the new test of fit. The proposed test and its implementation are thoroughly discussed, and an extended simulation study has been undertaken to clarify issues related to its implementation and explore the extent of its capabilities. A real data case is also investigated.
Alex Karagrigoriou, Ioannis Mavrogiannis, Georgia Papasotiriou, Ilia Vonta. An Exponentiality Test of Fit Based on a Tail Characterization against Heavy and Light-Tailed Alternatives. Risks, 2023, 11 (10), pp.169. ⟨10.3390/risks11100169⟩. ⟨hal-04543899⟩
Mathis Pasquier, Stéphane Jay, Jérôme Jacob, Pierre Sagaut. A Lattice-Boltzmann-Based Modelling Chain for Traffic-Related Atmospheric Pollutant Dispersion at the Local Urban Scale. Building and Environment, 2023, 242, pp.110562. ⟨10.1016/j.buildenv.2023.110562⟩. ⟨hal-04190005⟩ Plus de détails...
Urban traffic-related air pollution is a major source of environmental and health damage and is difficult to quantify due to its inherent physical complexity. We construct a CFD-based simulation framework coupling an efficient numerical method for turbulent fluid flows with a microscopic traffic model and an emissions model to simulate road transport pollutant dispersion at the urban microscale. We improve the open-source Lattice-Boltzmann based CFD software OpenLB to overcome its original stability deficiencies for high Reynolds number flows. A stable recursive regularization procedure with a double distribution function approach is proposed to solve an advection diffusion equation for passive scalar transport at high Reynolds number. The code is successfully validated on three reference cases of increasing complexity and the traffic model SUMO along with a physical engine emissions model are coupled with OpenLB to simulate traffic-induced pollution from a road network in a realistic complex geometry. Transient flow features are analysed and the time-averaged concentration levels in different neighbourhoods of the considered geometry are evaluated: high concentration levels are observed close to the streets but also inside specific building infrastructures due to complex wind dynamics. Analyses of altitudinal concentration variations show that flow recirculations located close to traffic lights can drive pollutant over the buildings and increase concentration levels inside inner courtyards. Time-averaged concentration maps are constructed using both spatially uniform and non-uniform line sources and it is shown that using uniform sources leads to up to 20% local concentration overestimations inside the urban canopy.
Mathis Pasquier, Stéphane Jay, Jérôme Jacob, Pierre Sagaut. A Lattice-Boltzmann-Based Modelling Chain for Traffic-Related Atmospheric Pollutant Dispersion at the Local Urban Scale. Building and Environment, 2023, 242, pp.110562. ⟨10.1016/j.buildenv.2023.110562⟩. ⟨hal-04190005⟩
Isabelle Cheylan, Tom Fringand, Jérôme Jacob, Julien Favier. Analysis of the immersed boundary method for turbulent fluid-structure interaction with Lattice Boltzmann method. Journal of Computational Physics, 2023, 492, pp.112418. ⟨10.1016/j.jcp.2023.112418⟩. ⟨hal-04543923⟩ Plus de détails...
L. Cappelli, N. Fedorczak, J. P. Gunn, S. Di Genova, J. Guterl, et al.. Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model. Plasma Physics and Controlled Fusion, 2023, 65 (9), pp.095001. ⟨10.1088/1361-6587/ace282⟩. ⟨hal-04190861⟩ Plus de détails...
In today’s nuclear fusion devices, erosion of high-Z metallic plasma-facing materials (PFMs) is mainly caused by physical sputtering. That is, by the exchange of energy between plasma ions and the atoms in the walls. In most of the numerical codes currently in use impinging plasma is approximated as a fluid. By averaging the incident particles’ energy distribution the high-energy population of the eroded material is underestimated. For heavy materials such as W, high-energy eroded particles tend to ionize far from the wall and they are less affected by the sheath electric field hence, not being attracted back to the wall, they have a higher chance to contaminate the core plasma. This could in turn result in an underestimation of the net erosion sources. In this work, a semi-analytical model was developed to include the energy distribution of the incident particles. Then, by Monte Carlo method, the net erosion of tungsten from a smooth PFM was calculated. The results show that the kinetic description in energy is important only for incident particles ionized once. For instance, it is particularly important for plasma ions such as Deuterium. It is seen that Deuterium contribution to the W net sources is not always negligible if compared to light impurities or to tungsten self-sputtering in the range of plasma parameters tested. Finally, results show that the difference between the fluid and kinetic models becomes more pronounced for high-screening plasma conditions.
L. Cappelli, N. Fedorczak, J. P. Gunn, S. Di Genova, J. Guterl, et al.. Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model. Plasma Physics and Controlled Fusion, 2023, 65 (9), pp.095001. ⟨10.1088/1361-6587/ace282⟩. ⟨hal-04190861⟩
Chenglei Wang, Simon Gsell, Umberto d'Ortona, Julien Favier. Generalized-Newtonian fluid transport by an instability-driven filament. Journal of Fluid Mechanics, 2023, 965, pp.A6. ⟨10.1017/jfm.2023.381⟩. ⟨hal-04544010⟩ Plus de détails...
Cilia are micro-scale hair-like organelles. They can exhibit self-sustained oscillations which play crucial roles in flow transport or locomotion. Recent studies have shown that these oscillations can spontaneously emerge from dynamic instability triggered by internal stresses via a Hopf bifurcation. However, the flow transport induced by an instability-driven cilium still remains unclear, especially when the fluid is non-Newtonian. This study aims at bridging these gaps. Specifically, the cilium is modelled as an elastic filament, and its internal actuation is represented by a constant follower force imposed at its tip. Three generalized Newtonian behaviours are considered, i.e. the shear-thinning, Newtonian and shear-thickening behaviours. Effects of four key factors, including the filament zero-stress shape, Reynolds number ( $Re$ ), follower-force magnitude and fluid rheology, on the filament dynamics, fluid dynamics and flow transport are explored through direct numerical simulation at $Re$ of 0.04 to 5 and through a scaling analysis at $Re \approx 0$ . The results reveal that even though it is expected that inertia vanishes at $Re \ll 1$ , inertial forces do alter the filament dynamics and deteriorate the flow transport at $Re\ge 0.04$ . Regardless of $Re$ , the flow transport can be improved when the flow is shear thinning or when the follower force increases. Furthermore, a linear stability analysis is performed, and the variation of the filament beating frequency, which is closely correlated with the filament dynamics and flow transport, can be predicted.
Chenglei Wang, Simon Gsell, Umberto d'Ortona, Julien Favier. Generalized-Newtonian fluid transport by an instability-driven filament. Journal of Fluid Mechanics, 2023, 965, pp.A6. ⟨10.1017/jfm.2023.381⟩. ⟨hal-04544010⟩
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨hal-04543708⟩ Plus de détails...
This work deals with 3D simulations of complex bubbly, cap-bubbly and churn regimes exhibiting bubbles of different shapes and with broad bubble size distribution. The first contribution of this work is to investigate and compare several bubble interaction mechanisms of coalescence and fragmentation for the 2-Group Interfacial Area Transport Equation (IATE) model. For two of these models, this is the first time their performances are assessed within a CFD code. The second contribution is to propose and assess a novel model of fragmentation and coalescence. Finally, a validation versus experimental data on three different configurations and three different regimes is performed. In particular, the interaction mechanisms are analysed for one specific regime. The implementation of the two-group IATE model has been systematically performed in the 3D NEPTUNE CFD code.
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨hal-04543708⟩
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨cea-04483130⟩ Plus de détails...
This work deals with 3D simulations of complex bubbly, cap-bubbly and churn regimes exhibiting bubbles of different shapes and with broad bubble size distribution. The first contribution of this work is to investigate and compare several bubble interaction mechanisms of coalescence and fragmentation for the 2-Group Interfacial Area Transport Equation (IATE) model. For two of these models, this is the first time their performances are assessed within a CFD code. The second contribution is to propose and assess a novel model of fragmentation and coalescence. Finally, a validation versus experimental data on three different configurations and three different regimes is performed. In particular, the interaction mechanisms are analysed for one specific regime. The implementation of the two-group IATE model has been systematically performed in the 3D NEPTUNE CFD code.
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨cea-04483130⟩
Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Immersed boundary based near-wall modeling for large eddy simulation of turbulent wall-bounded flow. Computers and Fluids, 2023, 259, pp.105893. ⟨10.1016/j.compfluid.2023.105893⟩. ⟨hal-04543910⟩ Plus de détails...
Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Immersed boundary based near-wall modeling for large eddy simulation of turbulent wall-bounded flow. Computers and Fluids, 2023, 259, pp.105893. ⟨10.1016/j.compfluid.2023.105893⟩. ⟨hal-04543910⟩
Minh Nguyen, Jean-François Boussuge, Pierre Sagaut, Juan-Carlos Larroya-Huguet. Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method. International Journal of Heat and Mass Transfer, 2023, 212, pp.124256. ⟨10.1016/j.ijheatmasstransfer.2023.124256⟩. ⟨hal-04546755⟩ Plus de détails...
Large eddy simulations of a row of seven jets emerging from a perforated pipe and impinging on a flat heated plate were carried out using a compressible hybrid thermal lattice Boltzmann solver. The average Reynolds number of the emerging jets was , with an exit-to-plate distance of 3 jet diameters. Two levels of upstream crossflow were simulated: one with weak cross flow, with a velocity ratio of , and one with strong cross flow, with a velocity ratio of . The flow field and heat transfer statistics were validated against experimental PIV and infrared thermography data from a recent study, showing good agreement. The effect of varying the Mach number on the wall heat transfer was subsequently tested. It was found that an increased Mach number lead to an increased value of the Nusselt number near the stagnation points.
Minh Nguyen, Jean-François Boussuge, Pierre Sagaut, Juan-Carlos Larroya-Huguet. Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method. International Journal of Heat and Mass Transfer, 2023, 212, pp.124256. ⟨10.1016/j.ijheatmasstransfer.2023.124256⟩. ⟨hal-04546755⟩
Journal: International Journal of Heat and Mass Transfer
G. Farag, P. Boivin, P. Sagaut. Linear interaction approximation for shock/disturbance interaction in a Noble–Abel stiffened gas. Shock Waves, 2023, ⟨10.1007/s00193-023-01131-8⟩. ⟨hal-04097657⟩ Plus de détails...
When departure from the ideal gas equation of state is considered, the Noble-Abel stiffened gas model is an appealing and versatile candidate due to its simple form. The Linear Interaction Approximation formalism is extended to consider non-ideal gas effects introduced by this equation of state. Kovásznay decomposition and adequate definition of the energy of disturbances are provided in the context of this equation of state. Changes with respect to ideal gas are investigated on transfer functions, critical angle and compression factor. Those differences yield concrete effects on the damping and transfer of fluctuations across shock waves. Those changes are further illustrated by considering the interaction of an entropy spot with a Mach 3 stationary shock wave.
G. Farag, P. Boivin, P. Sagaut. Linear interaction approximation for shock/disturbance interaction in a Noble–Abel stiffened gas. Shock Waves, 2023, ⟨10.1007/s00193-023-01131-8⟩. ⟨hal-04097657⟩
Hasan Misaii, Mitra Fouladirad, Firoozeh Haghighi. Optimal task-driven time-dependent covariate-based maintenance policy. Journal of Computational and Applied Mathematics, 2023, pp.115315. ⟨10.1016/j.cam.2023.115315⟩. ⟨hal-04162527⟩ Plus de détails...
Jérémie Labasse, Uwe Ehrenstein, Guillaume Fasse, Frédéric Hauville. Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion. Ocean Engineering, 2023, 275, pp.114169. ⟨10.1016/j.oceaneng.2023.114169⟩. ⟨hal-04032117⟩ Plus de détails...
A numerical solution procedure using the mesh-superposition approach, known as the Chimera method, together with the OpenFOAM toolbox environment is used to compute the forces generated by large amplitude heaving and pitching foil. The possibility of fitting thrust prediction laws, based on classical potential flow theories, with the numerically computed forces is explored, for a Reynolds number of 5 10 4. It is shown, first for a pure heaving motion and subsequently by adding a harmonic pitching motion, that theoretical scaling may be fitted to numerical time-averaged thrust data, even in the case of large amplitude motions. The thrust-prediction law is shown to still apply to pitching-rotating motions, such as those of blades in cycloidal propulsion devices, the mean pressure correction due to the additional surging motion being small. The synchronized rotation-pitching of three foils typical of a cross-flow propeller configuration is addressed as well. The numerical global thrust results are shown to be in general agreement with the theoretical prediction, but also with blade-embedded load cell measurements for an experimental device developed by the French Naval Academy Research Institute.
Jérémie Labasse, Uwe Ehrenstein, Guillaume Fasse, Frédéric Hauville. Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion. Ocean Engineering, 2023, 275, pp.114169. ⟨10.1016/j.oceaneng.2023.114169⟩. ⟨hal-04032117⟩
Alexandre Di-Marco, Jerome Jacob, Pierre Sagaut. Unsteady characteristics of pressure and swirl distortion in helicopter intake: A lattice Boltzmann method approach. Aerospace Science and Technology, 2023, 138, pp.108333. ⟨10.1016/j.ast.2023.108333⟩. ⟨hal-04543807⟩ Plus de détails...
The present paper focuses on the analysis of the unsteady characteristics of pressure and swirl distortion and their relationship inside a complex air intake, including a plenum chamber, using Large-Eddy Simulation based on the lattice Boltzmann method (LBM). The steady-state analysis of the pressure field and swirl angle in the Aerodynamic Interface Plane (AIP) shows a complex pressure and swirl distortion pattern, as well as a high level of unsteadiness. Additionally, two vortical structures with equal intensity located on the top and bottom sides of the AIP plane were identified. The unsteady pressure distortion analysis highlighted fluctuations between two positions of the maximum circumferential pressure distortion in the AIP plane. One of these positions presents mean and peak distortion values lower than the other position. Furthermore, an alternating vortex pattern between two swirl patterns in the AIP plane is also identified. Finally, the relationship between pressure and swirl unsteadiness was investigated, and a link between the swirl distortion pattern and pressure distortion was identified. The identification of this relationship will allow geometrical changes in the air intake, leading to a reduction of the average circumferential distortion level, as well as a reduction of the maximum peak level achievable during a flight phase.
Alexandre Di-Marco, Jerome Jacob, Pierre Sagaut. Unsteady characteristics of pressure and swirl distortion in helicopter intake: A lattice Boltzmann method approach. Aerospace Science and Technology, 2023, 138, pp.108333. ⟨10.1016/j.ast.2023.108333⟩. ⟨hal-04543807⟩
Imran Afgan, Yacine Kahil, Sofiane Benhamadouche, Mohamed Ali, Ahmed Alkaabi, et al.. Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations. International Journal of Heat and Fluid Flow, 2023, 100, pp.109115. ⟨10.1016/j.ijheatfluidflow.2023.109115⟩. ⟨hal-04546846⟩ Plus de détails...
This study analyses the heat transfer and flow characteristics of cross-flow over two heated infinite cylinders in a tandem (in-line) configuration. Non-isothermal Large Eddy Simulations (LES) using the dynamic Smagorinsky model were conducted at a fixed Reynolds number of 3, 000 (based on the free stream velocity and the cylinder diameter). A range of cylinder gap ratios (1.0 ≤ L/D ≤ 5.0) was investigated (in increments of 0.25) with two different Prandtl numbers Pr = 0.1 and 1.0. Results show that the flow structures vary according to the order of the patterns: (i) Extended body regime: without attachment for low L/D (1.0 1.25) where cylinders behave as a single bluff body with top–bottom vortex shedding, (ii) Shear layer reattachment regime: with reattachment for moderate L/D (1.5 3.75) where the detached shear layer from the upstream cylinder reattaches to the down- stream cylinder, and (iii) Co-shedding regime: for high gap ratios (3.75 ≤ L/D ≤ 5.0) a phenomenon called “jumping”, where the two cylinders behave as isolated bluff bodies. Furthermore, it was observed that the average Nusselt number of both cylinders experience a drastic variation at a critical spacing ratio (between 3.75 ≤ L/D ≤ 4.0). For L/D ≤ 3.0, the average Nusselt number of the upstream cylinder was found to be higher than that of the downstream one. However, for spacing ratios L/D > 3.0, the average Nusselt number was similar for both cylinders. For the downstream cylinder, the maximum Nusselt number was located at the separation angle and was found to be independent of the spacing ratio
Imran Afgan, Yacine Kahil, Sofiane Benhamadouche, Mohamed Ali, Ahmed Alkaabi, et al.. Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations. International Journal of Heat and Fluid Flow, 2023, 100, pp.109115. ⟨10.1016/j.ijheatfluidflow.2023.109115⟩. ⟨hal-04546846⟩
Journal: International Journal of Heat and Fluid Flow
Thomas Gianoli, Jean‐françois Boussuge, Pierre Sagaut, Jérôme de Laborderie. Development and validation of Navier–Stokes characteristic boundary conditions applied to turbomachinery simulations using the lattice Boltzmann method. International Journal for Numerical Methods in Fluids, 2023, 95 (4), pp.528-556. ⟨10.1002/fld.5160⟩. ⟨hal-04063964⟩ Plus de détails...
This article reports a procedure to implement as well as to validate non-reflecting boundary conditions applied for turbomachinery simulations, using Navier-Stokes characteristic boundary conditions in a compressible lattice Boltzmann solver. The implementation of both an inlet condition imposing total pressure, total temperature, and flow angles, as well as an outlet condition imposing a static pressure profile that allows the simulation to reach a simplified radial equilibrium, is described within the context of a lattice Boltzmann approach. The treatment at the boundaries relies on the characteristic methodology to derive conditions which are non-reflecting in terms of acoustics and is also compatible with turbulence injection at the inlet. These properties are evaluated on test cases of increasing complexity, ranging from a simple 2D periodic domain to an S-duct stage with turbulence injection.
Thomas Gianoli, Jean‐françois Boussuge, Pierre Sagaut, Jérôme de Laborderie. Development and validation of Navier–Stokes characteristic boundary conditions applied to turbomachinery simulations using the lattice Boltzmann method. International Journal for Numerical Methods in Fluids, 2023, 95 (4), pp.528-556. ⟨10.1002/fld.5160⟩. ⟨hal-04063964⟩
Journal: International Journal for Numerical Methods in Fluids
Richard M Lueptow, Rainer Hollerbach, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 1. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), ⟨10.1098/rsta.2022.0140⟩. ⟨hal-03989060⟩ Plus de détails...
In 1923, the Philosophical Transactions published G. I. Taylor’s seminal paper on the stability of what we now call Taylor–Couette flow. In the century since the paper was published, Taylor’s ground-breaking linear stability analysis of fluid flow between two rotating cylinders has had an enormous impact on the field of fluid mechanics. The paper’s influence has extended to general rotating flows, geophysical flows and astrophysical flows, not to mention its significance in firmly establishing several foundational concepts in fluid mechanics that are now broadly accepted. This two-part issue includes review articles and research articles spanning a broad range of contemporary research areas, all rooted in Taylor’s landmark paper. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper (part 1)’.
Richard M Lueptow, Rainer Hollerbach, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 1. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), ⟨10.1098/rsta.2022.0140⟩. ⟨hal-03989060⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Rainer Hollerbach, Richard M Lueptow, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 2. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2246), ⟨10.1098/rsta.2022.0359⟩. ⟨hal-04057399⟩ Plus de détails...
In 1923, the Philosophical Transactions published G. I. Taylor’s seminal paper on the stability of what we now call Taylor–Couette flow. In the century since the paper was published, Taylor’s ground-breaking linear stability analysis of fluid flow between two rotating cylinders has had an enormous impact on the field of fluid mechanics. The paper’s influence has extended to general rotating flows, geophysical flows and astrophysical flows, not to mention its significance in firmly establishing several foundational concepts in fluid mechanics that are now broadly accepted. This two-part issue includes review articles and research articles spanning a broad range of contemporary research areas, all rooted in Taylor’s landmark paper. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper (part 2)’.
Rainer Hollerbach, Richard M Lueptow, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 2. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2246), ⟨10.1098/rsta.2022.0359⟩. ⟨hal-04057399⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
S. Di Genova, G. Ciraolo, A. Gallo, J. Romazanov, N. Fedorczak, et al.. First 3D modeling of tungsten erosion and migration in WEST discharges adopting a toroidally non-symmetric wall geometry. Nuclear Materials and Energy, 2023, 34, pp.101340. ⟨10.1016/j.nme.2022.101340⟩. ⟨hal-03988791⟩ Plus de détails...
Numerical analyses are a key tool to investigate tungsten (W) sources and contamination in W Environment steady-state tokamak (WEST) plasma discharges. Modelling activity was performed in order to study W erosion and migration at WEST plasma-facing components (PFCs), using for the first time a toroidally asymmetric wall geometry provided by toroidally localized objects representing WEST outer limiter or antennae. 3D non-axisymmetric SOLEDGE transport simulations were performed with simplifying assumptions (pure Deuterium plasma, fluid model for neutrals) to reproduce WEST boundary plasma, and used as background for ERO2.0 simulations modelling W erosion, re-deposition, and migration. On the sides of the toroidally localized limiters/antennae, two thin W stripes were considered in order to model WEST W antennae protections. Simulations suggest antennae protections contribution to dominate W contamination in the considered simulations settings, highlighting the need of further analyses with different configurations using this kind of tools.
S. Di Genova, G. Ciraolo, A. Gallo, J. Romazanov, N. Fedorczak, et al.. First 3D modeling of tungsten erosion and migration in WEST discharges adopting a toroidally non-symmetric wall geometry. Nuclear Materials and Energy, 2023, 34, pp.101340. ⟨10.1016/j.nme.2022.101340⟩. ⟨hal-03988791⟩
Ivan Kudashev, Anna Medvedeva, Nicolas Fedorszak, David Zarzoso, Manuel Scotto d’ Abusco, et al.. Development of a set of synthetic diagnostics for the WEST tokamak to confront 2D transport simulations and experimental data. Journal of Instrumentation, 2023, 18 (02), pp.C02058. ⟨10.1088/1748-0221/18/02/C02058⟩. ⟨hal-04010344⟩ Plus de détails...
Significant scientific effort has been focused on optimizing the scenarios and plasma parameters for tokamak operations. The lack of comprehensive understanding of underlying physical processes leads to simplifications used both in plasma simulation codes and for diagnostics, which is also complicated by the harsh plasma environment. One of the main tools to couple, check and verify these assumptions are the synthetic diagnostics. In this work we demonstrate current results of the development of the set of synthetic diagnostics for the WEST tokamak to couple experimental data with the SolEdge3X-HDG 2D transport code.
Ivan Kudashev, Anna Medvedeva, Nicolas Fedorszak, David Zarzoso, Manuel Scotto d’ Abusco, et al.. Development of a set of synthetic diagnostics for the WEST tokamak to confront 2D transport simulations and experimental data. Journal of Instrumentation, 2023, 18 (02), pp.C02058. ⟨10.1088/1748-0221/18/02/C02058⟩. ⟨hal-04010344⟩
Thomas Cartier-Michaud, Philippe Ghendrih, Virginie Grandgirard, Eric Serre. Verification and accuracy check of simulations with PoPe and iPoPe. Journal of Computational Physics, 2023, 474, pp.111759. ⟨10.1016/j.jcp.2022.111759⟩. ⟨hal-03871954⟩ Plus de détails...
The theoretical background of the PoPe and iPoPe verification scheme is presented. Verification is performed using the simulation output of production runs. The computing overhead is estimated to be at most 10%. PoPe or iPoPe calculations can be done offline provided the necessary data is stored, for example additional time slices, or online where iPoPe is more effective. The computing overhead is mostly that of storing the necessary data. The numerical error is determined and split into a part proportional to the operators, which are combined to form the equations to be solved, thus modifying their control parameters, completed by a residual error orthogonal to these operators. The accuracy of the numerical solution is determined by this modification of the control parameters. The PoPe and iPoPe methods are illustrated in this paper with simulations of a simple mechanical system with chaotic trajectories evolving into a strange attractor with sensitivity to initial conditions. We show that the accuracy depends on the particular simulation both because the properties of the numerical solution depend on the values of the control parameter, and because the target accuracy will depend on the problem that is addressed. One shows that for a case close to bifurcations between different states, the accuracy is determined by the level of detail of the bifurcation phenomena one aims at describing. A unique verification index, the PoPe index, is proposed to characterise the accuracy, and consequently the verification, of each production run. The PoPe output allows one to step beyond verification and analyse for example the numerical scheme efficiency. For the chosen example at fixed PoPe index, therefore at fixed numerical error, one finds that the higher order integration scheme, comparing order 4 to order 2 Runge-Kutta time stepping, reduces the computation cost by a factor 4.
Thomas Cartier-Michaud, Philippe Ghendrih, Virginie Grandgirard, Eric Serre. Verification and accuracy check of simulations with PoPe and iPoPe. Journal of Computational Physics, 2023, 474, pp.111759. ⟨10.1016/j.jcp.2022.111759⟩. ⟨hal-03871954⟩
D. Martinand, E. Serre, B. Viaud. Instabilities and routes to turbulence in rotating disc boundary layers and cavities. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), pp.20220135. ⟨10.1098/rsta.2022.0135⟩. ⟨hal-03989074⟩ Plus de détails...
Studied for more than a century, first in the field of geophysics, flows over rotating discs present a great diversity of complex instability behaviours that are not yet fully understood. While the primary instabilities are now well characterized experimentally, theoretically and numerically, their role in the transition mechanisms to turbulence remains an open question that still challenges the scientific community. This article brings together the main results of the literature related to the instabilities over rotating discs, but also in the connected problem of rotating cavities, and reviews the main scenarios currently assumed to describe the flow breakdown to turbulence. A particular focus is on more recent studies of generic flows in rotating cavities bounded by two coaxial rotating discs, that occur in many industrial systems, the performances of which and their improvement are linked to a better understanding of these mechanisms. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)’.
D. Martinand, E. Serre, B. Viaud. Instabilities and routes to turbulence in rotating disc boundary layers and cavities. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), pp.20220135. ⟨10.1098/rsta.2022.0135⟩. ⟨hal-03989074⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
J Varela, D Spong, L Garcia, Y Ghai, David Zarzoso, et al.. Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma. Plasma Physics and Controlled Fusion, 2023, 65 (12), pp.125004. ⟨10.1088/1361-6587/ad05d4⟩. ⟨hal-04541045⟩ Plus de détails...
The aim of this study is to analyze the effect of the neutral beam injector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs) in DIII-D plasma. The analysis is done using the linear and nonlinear versions of the gyro-fluid code FAR3d. A set of parametric analyses are performed modifying the nonlinear simulation EP β (NBI injection power), EP energy (NBI voltage) and the radial location of the EP density profile gradient (NBI radial deposition). The analysis indicates a transition from the soft (local plasma relaxation) to the hard MHD (global plasma relaxation) limit if the simulation EP β ⩾ 0.02 , leading to bursting MHD activity caused by radial AEs overlapping. MHD bursts cause an enhancement of the EP transport showing ballistic-like features as avalanche-like events. Simulations in the soft MHD limit show an increment of the EP density gradient as the EP β increases. On the other hand, there is a gradient upper limit in the hard MHD limit, consistent with the critical-gradient behavior. AEs induce shear flows and zonal current leading to the deformation of the flux surfaces and the safety factor profile, respectively, particularly strong for the simulation in the hard MHD limit. Simulations in the hard MHD regime show a decrease of the AE frequency in the saturation phase; this is caused by the destabilization of a transitional mode between a 9 / 3 − 10 / 3 TAE and a 9 / 3 RSAE that may explain the AE frequency down-sweeping observed in some DIII-D discharges. Reducing the EP energy in the nonlinear simulations leads to a weakening of the plasma perturbation. On the other hand, increasing the EP energy causes the opposite effect. Nonlinear simulations of off-axis NBI profiles indicate a lower plasma perturbation as the EP density gradient is located further away from the magnetic axis.
J Varela, D Spong, L Garcia, Y Ghai, David Zarzoso, et al.. Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma. Plasma Physics and Controlled Fusion, 2023, 65 (12), pp.125004. ⟨10.1088/1361-6587/ad05d4⟩. ⟨hal-04541045⟩
Pierre Sagaut, V.K. Suman, P. Sundaram, M.K. Rajpoot, Y.G. Bhumkar, et al.. Global spectral analysis: Review of numerical methods. Computers and Fluids, 2023, 261, pp.105915. ⟨10.1016/j.compfluid.2023.105915⟩. ⟨hal-04546492⟩ Plus de détails...
The design and analysis of numerical methods are usually guided by the following: (a) von Neumann analysis using Fourier series expansion of unknowns, (b) the modified differential equation approach, and (c) a more generalized approach that analyzes numerical methods globally, using Fourier–Laplace transform to treat the total or disturbance quantities in terms of waves. This is termed as the global spectral analysis (GSA). GSA can easily handle non-periodic problems, by invoking wave properties of the field through the correct numerical dispersion relation, which is central to the design and analysis. This has transcended dimensionality of the problem, while incorporating various physical processes e.g. by studying convection, diffusion and reaction as the prototypical elements involved in defining the physics of the problem. Although this is used for fluid dynamical problems, it can also explain many multi-physics and multi-scale problems. This review describes this powerful tool of scientific computing, with new results originating from GSA: (i) providing a common framework to analyze both hyperbolic and dispersive wave problems; (ii) analyze numerical methods by comparing physical and numerical dispersion relation, which leads to the new class of dispersion relation preserving (DRP) schemes; (iii) developing error dynamics as a distinct tool, identifying sources of numerical errors involving both the truncation and round-off error. Such studies of error dynamics provide the epistemic tool of analysis rather than an aleatoric tool, which depends on uncertainty quantification for high performance computing (HPC). One of the central themes of GSA covers the recent advances in understanding numerical phenomenon like focusing, which defied analysis so far. An application of GSA shown here for the objective evaluation of the so-called DNS by pseudo-spectral method for spatial discretization along with time integration by two-stage Runge–Kutta method is performed. GSA clearly shows that this should not qualify as DNS for multiple reasons. A new design of HPC methods for peta- and exa-flop computing tools necessary for parallel computing by compact schemes are also described.
Pierre Sagaut, V.K. Suman, P. Sundaram, M.K. Rajpoot, Y.G. Bhumkar, et al.. Global spectral analysis: Review of numerical methods. Computers and Fluids, 2023, 261, pp.105915. ⟨10.1016/j.compfluid.2023.105915⟩. ⟨hal-04546492⟩
Gauthier Wissocq, Said Taileb, Song Zhao, Pierre Boivin. A hybrid lattice Boltzmann method for gaseous detonations. Journal of Computational Physics, 2023, 494, pp.112525. ⟨10.1016/j.jcp.2023.112525⟩. ⟨hal-04244340⟩ Plus de détails...
This article is dedicated to the construction of a robust and accurate numerical scheme based on the lattice Boltzmann method (LBM) for simulations of gaseous detonations. This objective is achieved through careful construction of a fully conservative hybrid lattice Boltzmann scheme tailored for multi-species reactive flows. The core concept is to retain LBM low dissipation properties for acoustic and vortical modes by using the collide and stream algorithm for the particle distribution function, while transporting entropic and species modes via a specifically designed finite-volume scheme. The proposed method is first evaluated on common academic cases, demonstrating its ability to accurately simulate multi-species compressible and reactive flows with discontinuities: the convection of inert species, a Sod shock tube with two ideal gases and a steady one-dimensional inviscid detonation wave. Subsequently, the potential of this novel approach is demonstrated in one- and two-dimensional inviscid unsteady gaseous detonations, highlighting its ability to accurately recover detonation structures and associated instabilities for high activation energies. To the authors' knowledge, this study is the first successful simulation of detonation cellular structures capitalizing on the LBM collide and stream algorithm.
Gauthier Wissocq, Said Taileb, Song Zhao, Pierre Boivin. A hybrid lattice Boltzmann method for gaseous detonations. Journal of Computational Physics, 2023, 494, pp.112525. ⟨10.1016/j.jcp.2023.112525⟩. ⟨hal-04244340⟩
Jacob Johnston, Sarah Dischinger, Mostafa Nassr, Ji Yeon Lee, Pedram Bigdelou, et al.. A reduced-order model of concentration polarization in reverse osmosis systems with feed spacers. Journal of Membrane Science, 2023, 675, pp.121508. ⟨10.1016/j.memsci.2023.121508⟩. ⟨hal-04546833⟩ Plus de détails...
Feed spacers in reverse osmosis systems generate complex fluid flows that limit computational fluid dynamics (CFD) simulations to small length and time scales. That limits our ability to simulate mineral scaling and other membrane fouling phenomena, which occur over longer length and time scales. Thus motivated, we develop a reduced model that replaces the CFD simulation of the velocity field with an analytical model that mimics spacers. This focuses the remaining numerical effort on simulating the advection–diffusion equation governing solute transport. We motivate and validate the model with CFD simulations and bench-scale experiments of spacer filaments in three different arrangements, including cases of unsteady vortex shedding. We show that the model produces a roughly 10,000-fold speedup compared to CFD, and accurately reproduces CFD predictions of not only the average and maximum concentrations, but also the local concentration distribution along the membrane. We also demonstrate the model for simulating a feed channel with a length-to-height ratio of 200. The model provides a simple testbed for exploratory studies of multispecies transport, precipitation, and membrane fouling phenomena for which simulating spacers is often prohibitive.
Jacob Johnston, Sarah Dischinger, Mostafa Nassr, Ji Yeon Lee, Pedram Bigdelou, et al.. A reduced-order model of concentration polarization in reverse osmosis systems with feed spacers. Journal of Membrane Science, 2023, 675, pp.121508. ⟨10.1016/j.memsci.2023.121508⟩. ⟨hal-04546833⟩
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect condition-based maintenance for a gamma degradation process in presence of unknown parameters. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2023, 237 (3), pp.546-561. ⟨10.1177/1748006X221134132⟩. ⟨hal-03842177⟩ Plus de détails...
A system subject to degradation is considered. The degradation is modelled by a gamma process. A condition-based maintenance policy with perfect corrective and an imperfect preventive actions is proposed. The maintenance cost is derived considering a Markov-renewal process. The statistical inference of the degradation and maintenance parameters by the maximum likelihood method is investigated. A sensibility analysis to different parameters is carried out and the perspectives are detailed.
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect condition-based maintenance for a gamma degradation process in presence of unknown parameters. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2023, 237 (3), pp.546-561. ⟨10.1177/1748006X221134132⟩. ⟨hal-03842177⟩
Journal: Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability
Jingtao Ma, Qiuxiang Huang, Yi Zhu, Yuan-Qing Xu, Fang-Bao Tian. Effects of fluid rheology on dynamics of a capsule through a microchannel constriction. Physics of Fluids, 2023, 35 (9), pp.091901. ⟨10.1063/5.0165614⟩. ⟨hal-04546805⟩ Plus de détails...
This paper numerically investigates the impact of fluid rheology on the behaviors of a spherical capsule through a microchannel constriction. Different flow scenarios are considered: a Newtonian capsule in a viscoelastic matrix, a Newtonian capsule in a Newtonian matrix, and a viscoelastic capsule in a Newtonian matrix. The results demonstrate that the capsule's lengths undergo oscillations during the passage through the constriction, with three stages of evolution. When approaching the constriction, the capsule respectively experiences increase and decrease in its length and height. While within or exiting the constriction, the length of the capsule continuously decreases, and the height generally increases. As the capsule moves away from the constriction, the capsule relaxes to different profiles in different flows. Detailed analysis on the effects of the fluid viscoelasticity on the capsule's lengths in different stages is provided. In addition, the behaviors of a red blood cell passing through a microchannel constriction are also examined. This study sheds light on the complex behaviors of a spherical capsule and red blood cell in microchannel constriction, emphasizing the significant influence of fluid rheology on their deformation and shape changes.
Jingtao Ma, Qiuxiang Huang, Yi Zhu, Yuan-Qing Xu, Fang-Bao Tian. Effects of fluid rheology on dynamics of a capsule through a microchannel constriction. Physics of Fluids, 2023, 35 (9), pp.091901. ⟨10.1063/5.0165614⟩. ⟨hal-04546805⟩
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Opportunistic perfect preventive maintenance policy in presence of masked data. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2022, 236 (6), pp.1024-1036. ⟨10.1177/1748006X211058936⟩. ⟨hal-04064544⟩ Plus de détails...
In this paper, the maintenance optimization problem of multi-component system is considered. It is assumed that the exact cause of system failure might be masked. That is, the exact cause of failure is unknown, and we only know that it belongs to a set called mask set. Both opportunistic perfect preventive maintenance (OPPM) and perfect corrective maintenance are considered. Threshold of OPPM and inter-inspection interval are considered as decision parameters which are optimized using long-run cost rate criteria. The applicability of the proposed maintenance policy is investigated using an illustrative example.
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Opportunistic perfect preventive maintenance policy in presence of masked data. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2022, 236 (6), pp.1024-1036. ⟨10.1177/1748006X211058936⟩. ⟨hal-04064544⟩
Journal: Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability
Philippe Ghendrih, Guilhem Dif-Pradalier, Olivier Panico, Yanick Sarazin, Hugo Bufferand, et al.. Role of avalanche transport in competing drift wave and interchange turbulence. Journal of Physics: Conference Series, 2022, 2397, pp.012018. ⟨10.1088/1742-6596/2397/1/012018⟩. ⟨hal-04498387⟩ Plus de détails...
We complete the 2D 2-fields turbulence model previously used with an interchange-like instability by slightly modifying the parallel loss terms to drive drift wave instabilities. We show that the instability driven by temperature fluctuations of the sheath losses is identical to that of the drift wave turbulence. The linear analysis is performed and used to select control parameters that yield identical maximum growth rates for the interchange alone and drift wave alone instability. Combining the two instabilities doubles the maximum growth rate. The non-linear simulations are used to analyse the SOL width. The simulations allow one to identify a low field side SOL region where interchange and drift wave are unstable and a high field side SOL region where only the drift wave is unstable. The SOL profiles appear exponential in the region close to the source but depart from a simple exponential fall-off in the far SOL. The low field side SOL width is found to be larger in the interchange alone case, slightly smaller when both instabilities are present and finally narrower when only the drift waves. For the high field side SOL, without interchange, the drift wave SOL width is observed to be identical to that on the low field side and larger than that when both instabilities at play. The Sherwood dimensionless parameter, ratio of convective particle flux divided by the diffusive particle flux, is used to compare the efficiency of turbulent transport. The profiles of the Sherwood parameter for time and flux surface averaged transport indicate that turbulent transport is dominant close to the separatrix but is less effective towards the far SOL. The Sherwood parameter evolution, determined with the flux-surface averaged transport, indicates that outward avalanche transport with corrugations governs the case with interchange only. When combining the two instabilities, outward avalanche transport is less pronounced and inward avalanche transport is observed, reducing the overall turbulent transport efficiency. The avalanche transport with drift waves only compared to interchange only is found to be inhibited.
Philippe Ghendrih, Guilhem Dif-Pradalier, Olivier Panico, Yanick Sarazin, Hugo Bufferand, et al.. Role of avalanche transport in competing drift wave and interchange turbulence. Journal of Physics: Conference Series, 2022, 2397, pp.012018. ⟨10.1088/1742-6596/2397/1/012018⟩. ⟨hal-04498387⟩
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir Computing–Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , 2022, 31 (3), pp.311-339. ⟨10.25088/ComplexSystems.31.3.311⟩. ⟨hal-03838327⟩ Plus de détails...
A detailed parametric analysis is presented, where the recent method based on the reservoir computing paradigm, including its statistical robustness, is studied. It is observed that the prediction capabilities of the reservoir computing approach strongly depend on the random initialization of both the input and the reservoir layers. Special emphasis is put on finding the region in the hyperparameter space where the ensemble-averaged training and generalization errors together with their variance are minimized. The statistical analysis presented here is based on the projection on proper elements method.
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir Computing–Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , 2022, 31 (3), pp.311-339. ⟨10.25088/ComplexSystems.31.3.311⟩. ⟨hal-03838327⟩
Georis Billo, Michel Belliard, Pierre Sagaut. Comparison of several interpolation methods to reconstruct field data in the vicinity of a finite element immersed boundary. Computers & Mathematics with Applications, 2022, 123, pp.123-135. ⟨10.1016/j.camwa.2022.08.002⟩. ⟨hal-04064030⟩ Plus de détails...
Thermal-hydraulics safety requirements for the second and third generation of nuclear reactors led to the development of innovative passive safety systems. In particular, new devices must be developed involving numerical simulations for turbulent two-phase flows around complex geometries. To reduce the time-consuming mesh generation phase when testing various geometries, we use a fictitious domain approach. More specifically, we choose the Penalized Direct Forcing Method to take into account inflow obstacles. Following a recent work, involving the resolution of the one-phase incompressible Navier-Stokes equations using a projection scheme and the Finite Element Method, this paper focuses on different techniques to recover data from the discrete immersed boundary and different ways to achieve order 2 in space via linear interpolation. Indeed, we investigate two data reconstruction approaches (one based on various weighted averaging, the other based on optimization) and compare their results for cylindrical and NACA0012 airfoil shapes: they provide similar accuracy but the weighting is much faster in terms of execution time. We also investigate three different interpolation types: unidirectional, multi-directional and a new hybrid between the two. The Taylor-Couette flow and the flow around a circular cylinder are used to carry out mesh convergence studies. Globally, order 2 in space is numerically assessed in both 2 and ∞ norms for all the interpolation types, which is consistent with theoretical expectations-even if the space convergence order is a bit higher for the multi-directional approach. For the flow around a circular cylinder, the values of aerodynamic coefficients and Strouhal number are in good agreement with the literature, especially when using directional interpolation. Finally, an industrial case, representative of passive safety systems, is presented to assess the robustness and capability of the method. The simulations tend to show that, here again, the directional interpolation offers the best behavior when dealing with complex geometries and relatively coarse meshes.
Georis Billo, Michel Belliard, Pierre Sagaut. Comparison of several interpolation methods to reconstruct field data in the vicinity of a finite element immersed boundary. Computers & Mathematics with Applications, 2022, 123, pp.123-135. ⟨10.1016/j.camwa.2022.08.002⟩. ⟨hal-04064030⟩
Journal: Computers & Mathematics with Applications
Ivan Kudashev, Anna Medvedeva, Manuel Scotto D’abusco, Nicolas Fedorszak, Stefano Di Genova, et al.. Development of a set of synthetic diagnostics for the confrontation between 2D transport simulations and WEST tokamak experimental data. Applied Sciences, 2022, 12 (19), pp.9807. ⟨10.3390/app12199807⟩. ⟨hal-03982630⟩ Plus de détails...
Transport codes are frequently used for describing fusion plasmas with the aim to prepare tokamak operations. Considering novel codes, such as SolEdge3X-HDG, synthetic diagnostics are a common technique used to validate new models and confront them with experimental data. The purpose of this study is to develop a set of synthetic diagnostics, starting from bolometer and visible cameras for the WEST tokamak, in order to compare the code results with the experimental data. This research is done in the framework of Raysect and Cherab Python libraries. This allows us to process various synthetic diagnostics in the same fashion in terms of 3D ray tracing with volume emitters developed specifically for fusion plasmas. We were able to implement the WEST tokamak model and the design of bolometer and visible cameras. Synthetic signals, based on full-discharge WEST plasma simulation, were used for to compare the SolEdge3X-HDG output plasma with experimental data. The study also considers the optical properties of the plasma-facing components (PFCs) and their influence on the performance of diagnostics. The paper shows a unified approach to synthetic diagnostic design, which will be further extended to cover the remaining diagnostics on the WEST tokamak.
Ivan Kudashev, Anna Medvedeva, Manuel Scotto D’abusco, Nicolas Fedorszak, Stefano Di Genova, et al.. Development of a set of synthetic diagnostics for the confrontation between 2D transport simulations and WEST tokamak experimental data. Applied Sciences, 2022, 12 (19), pp.9807. ⟨10.3390/app12199807⟩. ⟨hal-03982630⟩
S Mazzi, J Garcia, David Zarzoso, Ye Kazakov, J Ongena, et al.. Gyrokinetic study of transport suppression in JET plasmas with MeV-ions and toroidal Alfvén eigenmodes. Plasma Physics and Controlled Fusion, 2022, 64 (11), pp.114001. ⟨10.1088/1361-6587/ac91f3⟩. ⟨hal-03838290⟩ Plus de détails...
The impact of fast ions, generated in the MeV-range through the efficient application of the three-ion scheme in JET plasmas, on the turbulence properties is presented through complex numerical simulations. The suppression of the ion-scale turbulent transport is studied by means of in-depth gyrokinetic numerical analyses. Such a suppression is demonstrated to be achieved in the presence of toroidal Alfvén eigenmodes (TAEs) destabilized by the highly energetic ions. Details on the TAE excitation are also provided with a multi-code analysis. The inherently nonlinear and multi-scale mechanism triggered by the fast ions, also involving the high-frequency modes and the large-scale zonal flows, is deeply analyzed. Such mechanism is thus demonstrated, with experimental validating studies, to be the main cause of turbulence suppression and improvement of ion thermal confinement. Additional simulations address the implications of reversed shear magnetic equilibrium on the turbulent transport.
S Mazzi, J Garcia, David Zarzoso, Ye Kazakov, J Ongena, et al.. Gyrokinetic study of transport suppression in JET plasmas with MeV-ions and toroidal Alfvén eigenmodes. Plasma Physics and Controlled Fusion, 2022, 64 (11), pp.114001. ⟨10.1088/1361-6587/ac91f3⟩. ⟨hal-03838290⟩
Shang-Gui Cai, Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics. Physics of Fluids, 2022, 34 (9), pp.095106. ⟨10.1063/5.0098232⟩. ⟨hal-04065468⟩ Plus de détails...
This paper applies a recently developed immersed boundary-turbulence wall modeling approach to turbulent flows over a generic car geometry, known as the Ahmed body, under massive flow separation within a lattice Boltzmann solver. Although the immersed boundary method combined with hierarchical Cartesian grid offers high flexibility in automatic grid generation around complex geometries, the near-wall solution is significantly deteriorated compared to the body-fitted simulation, especially when coupled to wall models for turbulent flows at high Reynolds number. Enhanced wall treatments have been proposed in the literature and validated for attached flow configurations. In this work, the Ahmed body with a slant surface of angle 35 is considered where the flow separates massively over the slant surface and the vertical base. The large eddy simulation is performed with a Reynolds stress constraint near-wall. The eddy viscosity is computed dynamically by taking into account the actually resolved Reynolds stresses. It approaches the mixing length eddy viscosity in attached boundary layers and returns to the subgrid eddy viscosity in detached boundary layers. An explicit equilibrium wall model has also been proposed to accelerate the calculation. Comparison with the no-slip boundary condition on the separated surfaces shows that the near-wall treatments with the equilibrium wall model operate reasonably well on both attached and detached boundary layers.
Shang-Gui Cai, Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics. Physics of Fluids, 2022, 34 (9), pp.095106. ⟨10.1063/5.0098232⟩. ⟨hal-04065468⟩
Fatemeh Safaei, Jafar Ahmadi, Mitra Fouladirad. Optimal N-policy for the maintenance of k-out-of-n systems with dynamic minor repairs considering second-hand component income. International Journal of Production Research, 2022, pp.1-18. ⟨10.1080/00207543.2022.2120107⟩. ⟨hal-04064518⟩ Plus de détails...
This paper proposes a maintenance policy for a k-out-of-n: F system operating to fulfil several jobs without interruptions. The system is replaced when the Nth job completes or at the kth failure, whichever occurs first. So, there are some non-failed components when a replacement is done. These components can be sold as secondhand products to continue working in other systems for a while. The price of them is also considered in the proposed maintenance policy. An optimal maintenance policy is studied to minimise long-run average cost under the constraint of relative mean operating time. Comprehensive numerical studies are done to assess the effect of the model parameters on the optimal solutions. Also, to demonstrate the applicability of the proposed plan, a data set related to wind turbine generator failures is considered as a case study.
Fatemeh Safaei, Jafar Ahmadi, Mitra Fouladirad. Optimal N-policy for the maintenance of k-out-of-n systems with dynamic minor repairs considering second-hand component income. International Journal of Production Research, 2022, pp.1-18. ⟨10.1080/00207543.2022.2120107⟩. ⟨hal-04064518⟩
Journal: International Journal of Production Research
D Auroux, P Ghendrih, L Lamerand, F Rapetti, E Serre. Asymptotic behaviour, non-local dynamics and data assimilation tailoring of the reduced κ − ε model to address turbulent transport of fusion plasmas. Physics of Plasmas, 2022. ⟨hal-03811621⟩ Plus de détails...
The high-dimensional and multiscale nature of fusion plasma flows require the development of reduced models to be implemented in numerical codes capable of capturing the main features of turbulent transport in a sufficiently short time to be useful during tokamak operation. This paper goes further in the analysis of the dynamics of the κ − ε model based on the turbulent kinetic energy κ and its dissipation rate ε [Baschetti et al., Nuc. Fus 61, 106020 (2021)] to improve the predictability of the transverse turbulent transport in simulation codes. Present 1D results show further capabilities with respect to current models (based on constant effective perpendicular diffusion) and on the standard quasi-linear approach. The nonlinear dependence of D in κ and ε estimated from two additional transport equations allow to introduce some non-locality in the transport model. This is illustrated by the existence of parameter ranges with turbulence spreading. The paper also addresses another issue related to the uncertainties on the inherent free parameters of such reduced model. The study proposes a new approach in the fusion community based on a variational data assimilation involving the minimisation of a cost function defined as the distance between the reference data and the calculated values. The results are good, and show the ability of the data assimilation to reduce uncertainties on the free parameters, which remains a critical point to ensure the total reliability of such an approach.
D Auroux, P Ghendrih, L Lamerand, F Rapetti, E Serre. Asymptotic behaviour, non-local dynamics and data assimilation tailoring of the reduced κ − ε model to address turbulent transport of fusion plasmas. Physics of Plasmas, 2022. ⟨hal-03811621⟩
Samuele Mazzi, Yann Camenen, Jeronimo Garcia, David Zarzoso, D. Frigione, et al.. Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas. Nuclear Fusion, 2022, 62 (9), pp.096024. ⟨10.1088/1741-4326/ac7ac2⟩. ⟨hal-03838283⟩ Plus de détails...
Abstract The impact of the parallel flow shear on the tokamak plasma stability and turbulent transport driven by the ion temperature gradient (ITG) modes is analyzed by means of local gyrokinetic numerical analyses. It is shown that the parallel flow shear increases the ITG growth rate in the linear regime, and induces a broadening and shift of the radial spectrum. Then, the different effects of the finite parallel shear on the ITG turbulence characteristics are deeply analyzed in the nonlinear regime. These studies highlight that a reduction of the thermal-ion turbulent heat flux is induced by a complex mechanism involving the nonlinear generation of an enhanced zonal flow activity. Indeed, the turbulent sources of the zonal flows are increased by the introduction of the finite parallel flow shear in the system, beneficially acting on the saturation level of the ITG turbulence. The study has been carried out for the Waltz standard case below the critical threshold of the destabilization of the parallel velocity gradient instability, and then generalized to a selected pulse of a recent JET scenario with substantial toroidal rotation in the edge plasma region. It is, thus, suggested that the investigated complex mechanism triggered by the finite parallel flow shear reducing the ITG turbulent heat fluxes could be complementary to the well-established perpendicular flow shear in a region with sufficiently large plasma toroidal rotation.
Samuele Mazzi, Yann Camenen, Jeronimo Garcia, David Zarzoso, D. Frigione, et al.. Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas. Nuclear Fusion, 2022, 62 (9), pp.096024. ⟨10.1088/1741-4326/ac7ac2⟩. ⟨hal-03838283⟩
Tuan Dung Nguyen, Christophe Besse, François Rogier. High-order Scharfetter-Gummel-based schemes and applications to gas discharge modeling. Journal of Computational Physics, 2022, 461, pp.111196. ⟨10.1016/j.jcp.2022.111196⟩. ⟨hal-03352814⟩ Plus de détails...
A generalized Scharfetter-Gummel method is proposed to construct the numerical flux for one-dimensional drift-diffusion equations. Instead of taking a constant approximation of the flux as Scharfetter and Gummel did in [1], we consider a p-degree polynomial with p ≥ 1. The high order moments of the approximating flux function serve as intermediaries to bring numerical correction to the Scharfetter-Gummel flux, that the other end turns out to be the solution derivatives. Therefore, local solution reconstructions are required. The resulting schemes are high order and discretize at the same time the convective and diffusive fluxes without having to employ separately different methods to do so. The new schemes with p = 1 and p = 2 are employed to simulate atmospheric pressure discharge where they are applied to the continuity equations for electrons and ions, and solved simultaneously with Poisson's equation. Numerical results indicate that our method are robust and highly accurate.
Tuan Dung Nguyen, Christophe Besse, François Rogier. High-order Scharfetter-Gummel-based schemes and applications to gas discharge modeling. Journal of Computational Physics, 2022, 461, pp.111196. ⟨10.1016/j.jcp.2022.111196⟩. ⟨hal-03352814⟩
B. Bugeat, J.-Ch. Robinet, J.-C. Chassaing, P. Sagaut. Low-frequency resolvent analysis of the laminar oblique shock wave/boundary layer interaction. Journal of Fluid Mechanics, 2022, 942, pp.A43. ⟨10.1017/jfm.2022.390⟩. ⟨hal-04064039⟩ Plus de détails...
Resolvent analysis is used to study the low-frequency behaviour of the laminar oblique shock wave/boundary layer interaction (SWBLI). It is shown that the computed optimal gain, which can be seen as a transfer function of the system, follows a first-order low-pass filter equation, recovering the results of Touber & Sandham (J. Fluid Mech., vol. 671, 2011, pp. 417-465). This behaviour is understood as proceeding from the excitation of a single stable, steady global mode whose damping rate sets the time scale of the filter. Different Mach and Reynolds numbers are studied, covering different recirculation lengths L. This damping rate is found to scale as 1/L, leading to a constant Strouhal number St L as observed in the literature. It is associated with a breathing motion of the recirculation bubble. This analysis furthermore supports the idea that the low-frequency dynamics of the SWBLI is a forced dynamics, in which background perturbations continuously excite the flow. The investigation is then carried out for three-dimensional perturbations for which two regimes are identified. At low wavenumbers of the order of L, a modal mechanism similar to that of two-dimensional perturbations is found and exhibits larger values of the optimal gain. At larger wavenumbers, of the order of the boundary layer thickness, the growth of streaks, which results from a non-modal mechanism, is detected. No interaction with the recirculation region is observed. Based on these results, the potential prevalence of three-dimensional effects in the low-frequency dynamics of the SWBLI is discussed.
B. Bugeat, J.-Ch. Robinet, J.-C. Chassaing, P. Sagaut. Low-frequency resolvent analysis of the laminar oblique shock wave/boundary layer interaction. Journal of Fluid Mechanics, 2022, 942, pp.A43. ⟨10.1017/jfm.2022.390⟩. ⟨hal-04064039⟩
Mitra Fouladirad, Massimiliano Giorgio, Gianpaolo Pulcini. A transformed gamma process for bounded degradation phenomena. Quality and Reliability Engineering International, 2022, 39 (2), pp.546 - 564. ⟨10.1002/qre.3167⟩. ⟨hal-04063942⟩ Plus de détails...
Most of the stochastic models adopted to describe the evolution over time of degradation phenomena of technological units assume that their degradation level can increase indeterminately. However, these degradation phenomena are typically subjected to obvious bounds, if only because technological units have finite size. In fact, very often, this inconsistency does not significantly affect the effectiveness of unbounded degradation models, since degrading units are usually assumed to fail when their degradation level exceeds a failure threshold that is much smaller than the obvious bounds. Nevertheless, in some cases, due to the very nature of the underlying degradation mechanism, less obvious bounds could exist, which are not necessarily far from the failure thresholds. The question that arises is whether the use of a bounded degradation model, in this latter type of experimental situations, could be beneficial. For this purpose, since a bounded degradation process should necessarily have dependent increments, in this paper we investigate the potential of a new bounded transformed gamma (TG) process to adequately describe bounded degradation phenomena and predict their future evolution. Differently from other existing gamma process based bounded degradation models, here the upper bound is treated as an unknown parameter that has to be estimated from the available degradation data. A numerical example is presented where the parameters of the proposed model are estimated from simulated data. Then the model is applied to a set of wear measures of cylinder liners that equip a diesel engine for marine propulsion, which have also stimulated this study. Model parameters are estimated by using the maximum likelihood (ML) method. The fitting ability of the proposed new bounded process is compared to that of an unbounded gamma process, which was previously adopted to analyze the same liner wear data. Obtained results are critically discussed in the paper.
Mitra Fouladirad, Massimiliano Giorgio, Gianpaolo Pulcini. A transformed gamma process for bounded degradation phenomena. Quality and Reliability Engineering International, 2022, 39 (2), pp.546 - 564. ⟨10.1002/qre.3167⟩. ⟨hal-04063942⟩
Journal: Quality and Reliability Engineering International
J. Etminan, H. Kamranfar, M. Chahkandi, M. Fouladirad. Analysis of time-to-failure data for a repairable system subject to degradation. Journal of Computational and Applied Mathematics, 2022, 408, pp.114098. ⟨10.1016/j.cam.2022.114098⟩. ⟨hal-04063947⟩ Plus de détails...
In this paper, a gradually deteriorating system with imperfect repair is considered. The deterioration is modeled by a stationary stochastic process. The system fails once the deterioration level exceeds a given threshold L. At failure, an imperfect repair is performed and the deterioration level is reduced to a fixed value r, say. The system can be repaired n − 1 times and will be replaced after the nth failure. The article aims to estimate the parameters of the proposed deterioration process based on the observed failures. To this end we consider the Wiener and Gamma processes which are the most common used stochastic process models. In Wiener process, an explicit expression for the estimators is obtained. Birnbaum-Saunders approximation is extended to estimate the parameters in Gamma process. An optimal replacement policy is also discussed. Finally, a Monte-Carlo simulation is conducted to investigate the performance of estimators.
J. Etminan, H. Kamranfar, M. Chahkandi, M. Fouladirad. Analysis of time-to-failure data for a repairable system subject to degradation. Journal of Computational and Applied Mathematics, 2022, 408, pp.114098. ⟨10.1016/j.cam.2022.114098⟩. ⟨hal-04063947⟩
Journal: Journal of Computational and Applied Mathematics
Olivier Mesdjian, Chenglei Wang, Simon Gsell, Umberto D’ortona, Julien Favier, et al.. Longitudinal to Transverse Metachronal Wave Transitions in an In Vitro Model of Ciliated Bronchial Epithelium. Physical Review Letters, 2022, 129 (3), pp.038101. ⟨10.1103/PhysRevLett.129.038101⟩. ⟨hal-03741505⟩ Plus de détails...
Olivier Mesdjian, Chenglei Wang, Simon Gsell, Umberto D’ortona, Julien Favier, et al.. Longitudinal to Transverse Metachronal Wave Transitions in an In Vitro Model of Ciliated Bronchial Epithelium. Physical Review Letters, 2022, 129 (3), pp.038101. ⟨10.1103/PhysRevLett.129.038101⟩. ⟨hal-03741505⟩
Marwa Belhaj Salem, Mitra Fouladirad, Estelle Deloux. Variance Gamma process as degradation model for prognosis and imperfect maintenance of centrifugal pumps. Reliability Engineering and System Safety, 2022, 223, pp.108417. ⟨10.1016/j.ress.2022.108417⟩. ⟨hal-04063946⟩ Plus de détails...
This paper considers the degradation modelling of a non-monotonous health indicator. A Variance Gamma process is proposed for the degradation modelling and its calibration in presence of data is discussed. The remaining useful lifetime estimation based on this model is considered and its sensitivity to parameters estimates is analysed. The model is applied to real data of leakage rate of centrifugal pump. Eventually, an imperfect maintenance policy is proposed and optimized.
Marwa Belhaj Salem, Mitra Fouladirad, Estelle Deloux. Variance Gamma process as degradation model for prognosis and imperfect maintenance of centrifugal pumps. Reliability Engineering and System Safety, 2022, 223, pp.108417. ⟨10.1016/j.ress.2022.108417⟩. ⟨hal-04063946⟩
Journal: Reliability Engineering and System Safety
Hoda Kamranfar, Kambiz Ahmadi, Mitra Fouladirad. On inference in a class of exponential distribution under imperfect maintenance. Communications in Statistics - Simulation and Computation, 2022, pp.1-27. ⟨10.1080/03610918.2022.2103567⟩. ⟨hal-04064552⟩ Plus de détails...
This paper deals with statistical inference for lifetime data in presence of imperfect maintenance. For the maintenance model, the Sheu and Griffith model is considered. The lifetime distribution belongs to exponential distribution class. The maximum likelihood estimation procedure of the model parameters is discussed, and confidence intervals are provided using the asymptotic likelihood theory and bootstrap approach. Based on conjugate and discrete priors, Bayesian estimators of the model parameters are developed under symmetric and asymmetric loss functions. The proposed methodologies are applied to simulated data and sensitivity analysis to different parameters and data characteristics is carried out. The effect of model misspecification is also assessed within this class of distributions through a Monte Carlo simulation study. Finally, two datasets are analyzed for demonstrative aims.
Hoda Kamranfar, Kambiz Ahmadi, Mitra Fouladirad. On inference in a class of exponential distribution under imperfect maintenance. Communications in Statistics - Simulation and Computation, 2022, pp.1-27. ⟨10.1080/03610918.2022.2103567⟩. ⟨hal-04064552⟩
Journal: Communications in Statistics - Simulation and Computation
G. Piraccini, F. Schwander, E. Serre, G. Giorgiani, M. Scotto d'Abusco. Spatial adaptivity in SOLEDGE3X‐HDG for edge plasma simulations in versatile magnetic and reactor geometries. Contributions to Plasma Physics, 2022, 62 (5-6), ⟨10.1002/ctpp.202100185⟩. ⟨hal-04063959⟩ Plus de détails...
With the ultimate goal to predict plasmas heat and particle fluxes in ITER opera- tion, more efforts are required to deal with realistic magnetic configurations and tokamak geometries. In an attempt to achieve this goal, we propose an adaptive mesh refinement method added to a fluid solver based on a high-order hybrid discontinuous Galerkin (HDG) method. Based on unstructured meshes, this magnetic equilibrium free numerical scheme has shown promising and encour- aging features to solve 2D/3D transport reduced Braginski fluid equations. To improve its numerical efficiency, a mesh refinement based on h-adpativity is investigated. We describe here an adaptive refinement strategy on a reduced edge particle transport model based on electron density and parallel momentum. This strategy is illustrated in realistic tokamak wall geometry. Computations performed show potential gains in the required number of degrees of freedom against benchmark computations with uniform meshes, along with the poten- tial to give an automated, goal-oriented, mesh generation technique for edge transport simulations in 2D
G. Piraccini, F. Schwander, E. Serre, G. Giorgiani, M. Scotto d'Abusco. Spatial adaptivity in SOLEDGE3X‐HDG for edge plasma simulations in versatile magnetic and reactor geometries. Contributions to Plasma Physics, 2022, 62 (5-6), ⟨10.1002/ctpp.202100185⟩. ⟨hal-04063959⟩
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Optimal shock‐based maintenance policy for a system in a dynamic environment. Applied Stochastic Models in Business and Industry, 2022, 38 (6), pp.918 - 934. ⟨10.1002/asmb.2686⟩. ⟨hal-04063939⟩ Plus de détails...
In this article, we consider a single-unit system that operates in a dynamic environment and is subject to shocks. Shocks only affect the system (nonlethal shock) and do not cause sudden failure, and arrive according to a counting process. Both homogeneous and nonhomogeneous Poisson processes are considered for shocks arrival modeling. In order to model the dynamic environment and consider shock effects, a multiplicative failure rate model is proposed. Both corrective maintenance and shock-based preventive maintenance are considered, and two policies are proposed. In the first proposed policy, the system is replaced by a new one upon a failure or based on the predetermined number of shocks, whichever comes first, while the second proposed policy extends the first one by considering an imperfect preventive repair at each inspection time. The inspection times are periodic and the interinspection interval is considered as a decision variable. The proposed policies are optimized according to long-run cost rate criteria. Numerical examples illustrate the applicability and efficiency of the proposed policies.
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Optimal shock‐based maintenance policy for a system in a dynamic environment. Applied Stochastic Models in Business and Industry, 2022, 38 (6), pp.918 - 934. ⟨10.1002/asmb.2686⟩. ⟨hal-04063939⟩
Journal: Applied Stochastic Models in Business and Industry
Antoine Galko, Simon Gsell, Umberto d'Ortona, Laurent Morin, Julien Favier. Pulsated Herschel-Bulkley flows in two-dimensional channels: A model for mucus clearance devices. Physical Review Fluids, 2022, 7 (5), pp.053301. ⟨10.1103/PhysRevFluids.7.053301⟩. ⟨hal-03863329⟩ Plus de détails...
M. Nguyen, J. Boussuge, P. Sagaut, J. Larroya-Huguet. Large eddy simulation of a thermal impinging jet using the lattice Boltzmann method. Physics of Fluids, 2022, 34 (5), pp.055115. ⟨10.1063/5.0088410⟩. ⟨hal-03669901⟩ Plus de détails...
A compressible Hybrid Lattice Boltzmann Method solver is used to perform a wall-resolved Large eddy simulation of an isothermal axisymmetric jet issuing from a pipe and impinging on a heated flat plate at a Reynolds number of 23 000, a Mach number of 0.1, and an impingement distance of two jet diameters. The jet flow field statistics, Nusselt number profile (including the secondary peak), and shear stress profile were well reproduced. The azimuthal coherence of the primary vortical structures was relatively low, leading to no discernible temporal periodicity of the azimuthally averaged Nusselt number at the location of the secondary peak. While local unsteady near-wall flow separation was observed in the wall jet, this flow separation did not exhibit azimuthal coherence and was not found to be the only cause of the thermal spots blue, which lead to the secondary peak in the Nusselt number, as stream-wise oriented structures also played a significant role in increasing the local heat transfer.
M. Nguyen, J. Boussuge, P. Sagaut, J. Larroya-Huguet. Large eddy simulation of a thermal impinging jet using the lattice Boltzmann method. Physics of Fluids, 2022, 34 (5), pp.055115. ⟨10.1063/5.0088410⟩. ⟨hal-03669901⟩
Guanxiong Wang, Song Zhao, Pierre Boivin, Eric Serre, Pierre Sagaut. A new hybrid lattice-Boltzmann method for thermal flow simulations in low-Mach number approximation. Physics of Fluids, 2022, 34 (4), pp.046114. ⟨10.1063/5.0091517⟩. ⟨hal-03796386⟩ Plus de détails...
A new low-Mach algorithm for the thermal lattice Boltzmann method (LBM) is proposed aiming at reducing the computational cost of thermal flow simulations in the low Mach number limit. The well-known low Mach number approximation is adopted to accelerate the simulations by enlarging the time step through re-scaling the psuedoacoustic speed to the same order of the fluid motion velocity. This specific process is inspired by the similarity between the artificial compressibility method and the isothermal LBM and is further extended to its thermal counterpart. It must be emphasized that such low-Mach acceleration strategy is in a general form, thus can be easily applied to other compressible LB methods. The present method overcomes the drawback of the classical pressure gradient scaling method due to the pressure gradient changing. The new algorithm is validated by various well-documented academic test cases in laminar [one dimensional gravity column, 2D (two dimensional) rising thermal bubble, and 2D differentially heated square cavity] and turbulent [3D (three dimensional) Taylor–Green vortex and 3D heated cylinder] regimes. All the results show excellent agreement with the reference data and high computational efficiency.
Guanxiong Wang, Song Zhao, Pierre Boivin, Eric Serre, Pierre Sagaut. A new hybrid lattice-Boltzmann method for thermal flow simulations in low-Mach number approximation. Physics of Fluids, 2022, 34 (4), pp.046114. ⟨10.1063/5.0091517⟩. ⟨hal-03796386⟩
H Bufferand, J Balbin, S Baschetti, J Bucalossi, G Ciraolo, et al.. Implementation of multi-component Zhdanov closure in SOLEDGE3X. Plasma Physics and Controlled Fusion, 2022, 64 (5), pp.055001. ⟨10.1088/1361-6587/ac4fac⟩. ⟨hal-03981783⟩ Plus de détails...
The multi-component fluid closure derived by Zhdanov (2002 Transport Processes in Multicomponent Plasma (London: Taylor and Francis)) is implemented in the fluid code SOLEDGE3X-EIRENE to deal with arbitrary edge plasma composition. The closure assumes no distinction between species such as light versus heavy species separation. The work of Zhdanov is rewritten in a matricial form in order to clearly link friction forces and heat fluxes to the different species velocities and temperature gradients.
H Bufferand, J Balbin, S Baschetti, J Bucalossi, G Ciraolo, et al.. Implementation of multi-component Zhdanov closure in SOLEDGE3X. Plasma Physics and Controlled Fusion, 2022, 64 (5), pp.055001. ⟨10.1088/1361-6587/ac4fac⟩. ⟨hal-03981783⟩
Rouae Ben Dhia, Nils Tilton, Denis Martinand. Impact of osmotic pressure on the stability of Taylor vortices. Journal of Fluid Mechanics, 2022, 933, pp.A51. ⟨10.1017/jfm.2021.1101⟩. ⟨hal-03533753⟩ Plus de détails...
We use linear stability analysis and direct numerical simulations to investigate the coupling between centrifugal instabilities, solute transport and osmotic pressure in a Taylor–Couette configuration that models rotating dynamic filtration devices. The geometry consists of a Taylor–Couette cell with a superimposed radial throughflow of solvent across two semi-permeable cylinders. Both cylinders totally reject the solute, inducing the build-up of a concentration boundary layer. The solute retroacts on the velocity field via the osmotic pressure associated with the concentration differences across the semi-permeable cylinders. Our results show that the presence of osmotic pressure strongly alters the dynamics of the centrifugal instabilities and substantially reduces the critical conditions above which Taylor vortices are observed. It is also found that this enhancement of the hydrodynamic instabilities eventually plateaus as the osmotic pressure is further increased. We propose a mechanism to explain how osmosis and instabilities cooperate and develop an analytical criterion to bound the parameter range for which osmosis fosters the hydrodynamic instabilities.
Rouae Ben Dhia, Nils Tilton, Denis Martinand. Impact of osmotic pressure on the stability of Taylor vortices. Journal of Fluid Mechanics, 2022, 933, pp.A51. ⟨10.1017/jfm.2021.1101⟩. ⟨hal-03533753⟩
David Zarzoso, Diego Del-Castillo-Negrete, Rémi Lacroix, Pierre-Eric Bernard, Stanislas Touzet. Transport and losses of fusion-born alpha particles in the presence of tearing modes using the new Toroidal Accelerated Particle Simulator (TAPaS). Plasma Physics and Controlled Fusion, 2022, 64 (4), pp.044003. ⟨10.1088/1361-6587/ac493a⟩. ⟨hal-03843243⟩ Plus de détails...
Abstract The transport and losses of fusion-born alpha particles are studied in the presence of a single-helicity tearing mode, characterized by ( m = 2 , n = 1 ). The analysis is performed by means of the recently developed Toroidal Accelerated P a rticle Simulator ( TAPaS ). Although such modes have usually been believed to result only in a local flattening of the radial profiles, it is shown that the density profile can exhibit a global modification leading to significant losses of alpha particles. This is due to the fact that, although the magnetic field does not exhibit any chaotic behaviour, the trajectories of alpha particles do, as revealed by their Poincaré maps. Such results are in qualitative agreement with past observations and simulations of energetic particles generated by neutral beam injection in TFTR, DIII-D and AUG tokamaks. In-depth analysis is carried out to characterize the impact of the tearing mode on the transport and losses of fusion-born alpha-particles with a realistic density profile. The impact of the amplitude is evidenced. Moreover, the effect of the island rotation frequency is assessed based on a detailed analysis of the linear resonances in phase-space, in agreement with the simulation results. Finally, the probability density function of the exit time has been computed and the transport of alpha particles has been found to be anomalous.
David Zarzoso, Diego Del-Castillo-Negrete, Rémi Lacroix, Pierre-Eric Bernard, Stanislas Touzet. Transport and losses of fusion-born alpha particles in the presence of tearing modes using the new Toroidal Accelerated Particle Simulator (TAPaS). Plasma Physics and Controlled Fusion, 2022, 64 (4), pp.044003. ⟨10.1088/1361-6587/ac493a⟩. ⟨hal-03843243⟩
M Raghunathan, Y Marandet, H Bufferand, G Ciraolo, Ph Ghendrih, et al.. Multi-temperature Generalized Zhdanov Closure for Scrape-Off Layer/Edge Applications. Plasma Physics and Controlled Fusion, 2022. ⟨hal-03810579⟩ Plus de détails...
The derivation of the multi-temperature generalized Zhdanov closure is provided starting from the most general form of the left hand side of the moment averaged kinetic equation with the Sonine-Hermite polynomial ansatz for an arbitrary number of moments. The process of arriving at the reduced higher-order moment equations, with its assumptions and approximations, is explicitly outlined. The generalized multi-species, multi-temperature coefficients from the authors' previous article are used to compute values of higher order moments such as heat flux in terms of the lower order moments. Transport coefficients and the friction and thermal forces for magnetic confinement fusion relevant cases with the generalized coefficients are compared to the scheme with the single-temperature coefficients previously provided by Zhdanov et al. It is found that the 21N-moment multi-temperature coefficients are adequate for most cases relevant to fusion. Furthermore, the 21N-moment scheme is also tested against the trace approximation to determine the range of validity of the trace approximation with respect to fusion relevant plasmas. Possible refinements to the closure scheme are illustrated as well, in order to account for quantities which might be significant in certain schemes such as the drift approximation.
M Raghunathan, Y Marandet, H Bufferand, G Ciraolo, Ph Ghendrih, et al.. Multi-temperature Generalized Zhdanov Closure for Scrape-Off Layer/Edge Applications. Plasma Physics and Controlled Fusion, 2022. ⟨hal-03810579⟩
X Litaudon, F Jenko, D Borba, D Borodin, B J Braams, et al.. EUROfusion-theory and advanced simulation coordination (E-TASC): programme and the role of high performance computing. Plasma Physics and Controlled Fusion, 2022, 64 (3), pp.034005. ⟨10.1088/1361-6587/ac44e4⟩. ⟨hal-03562886⟩ Plus de détails...
Abstract This paper is a written summary of an overview oral presentation given at the 1st Spanish Fusion High Performance Computer (HPC) Workshop that took place on the 27 November 2020 as an online event. Given that over the next few years ITER 24 24 ITER (‘The Way’ in Latin) is the world’s largest tokamak under construction in the south of France: a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy ( https://www.iter.org/ ). will move to its operation phase and the European-DEMO design will be significantly advanced, the EUROfusion consortium has initiated a coordination effort in theory and advanced simulation to address some of the challenges of the fusion research in Horizon EUROPE (2021–2027), i.e. the next EU Framework Programme for Research and Technological Development. This initiative has been called E-TASC, which stands for EUROfusion-Theory and Advanced Simulation Coordination. The general and guiding principles of E-TASC are summarized in this paper. In addition, an overview of the scientific results obtained in the pilot phase (2019–2020) of E-TASC are provided while highlighting the importance of the required progress in computational methods and HPC techniques. In the initial phase, five pilot theory and simulation tasks were initiated: towards a validated predictive capability of the low to high transition and pedestal physics; runaway electrons in tokamak disruptions in the presence of massive material injection; fast code for the calculation of neoclassical toroidal viscosity in stellarators and tokamaks; development of a neutral gas kinetics modular code; European edge and boundary code for reactor-relevant devices. In this paper, we report on recent progress made by each of these projects.
X Litaudon, F Jenko, D Borba, D Borodin, B J Braams, et al.. EUROfusion-theory and advanced simulation coordination (E-TASC): programme and the role of high performance computing. Plasma Physics and Controlled Fusion, 2022, 64 (3), pp.034005. ⟨10.1088/1361-6587/ac44e4⟩. ⟨hal-03562886⟩
Gauthier Wissocq, Pierre Sagaut. Hydrodynamic limits and numerical errors of isothermal lattice Boltzmann schemes. Journal of Computational Physics, 2022, 450, pp.110858. ⟨10.1016/j.jcp.2021.110858⟩. ⟨hal-04064045⟩ Plus de détails...
With the aim of better understanding the numerical properties of the lattice Boltzmann method (LBM), a general methodology is proposed to derive its hydrodynamic limits in the discrete setting. It relies on a Taylor expansion in the limit of low Knudsen numbers. With a single asymptotic analysis, two kinds of deviations with the Navier-Stokes (NS) equations are explicitly evidenced: consistency errors, inherited from the kinetic description of the LBM, and numerical errors attributed to its space and time discretization. The methodology is applied to the Bhatnagar-Gross-Krook (BGK), the regularized and the multiple relaxation time (MRT) collision models in the isothermal framework. Deviation terms are systematically confronted to linear analyses in order to validate their expressions, interpret them and provide explanations for their numerical properties. The low dissipation of the BGK model is then related to a particular pattern of its error terms in the Taylor expansion. Similarly, dissipation properties of the regularized and MRT models are explained by a phenomenon referred to as hyperviscous degeneracy. The latter consists in an unexpected resurgence of high-order Knudsen effects induced by a large numerical prefactor. It is at the origin of over-dissipation and severe instabilities in the low-viscosity regime.
Gauthier Wissocq, Pierre Sagaut. Hydrodynamic limits and numerical errors of isothermal lattice Boltzmann schemes. Journal of Computational Physics, 2022, 450, pp.110858. ⟨10.1016/j.jcp.2021.110858⟩. ⟨hal-04064045⟩
D. Galassi, C. Theiler, T. Body, F. Manke, P. Micheletti, et al.. Validation of edge turbulence codes in a magnetic X-point scenario in TORPEX. Physics of Plasmas, 2022, 29 (1), pp.012501. ⟨10.1063/5.0064522⟩. ⟨hal-03566373⟩ Plus de détails...
D. Galassi, C. Theiler, T. Body, F. Manke, P. Micheletti, et al.. Validation of edge turbulence codes in a magnetic X-point scenario in TORPEX. Physics of Plasmas, 2022, 29 (1), pp.012501. ⟨10.1063/5.0064522⟩. ⟨hal-03566373⟩
M Scotto d'Abusco, G Giorgiani, J F Artaud, H Bufferand, G Ciraolo, et al.. Core-edge 2D fluid modeling of full tokamak discharge with varying magnetic equilibrium: from WEST start-up to ramp-down. Nuclear Fusion, 2022, ⟨10.1088/1741-4326/ac47ad⟩. ⟨hal-03509800⟩ Plus de détails...
In the present work we investigate for the first time the 2D fluid transport of the plasma in WEST during an entire discharge from the start-up to the ramp-down (shot #54487). The evolution of density profile, electron and ion temperatures together with the experimental magnetic equilibrium, total current and gas-puff rate is investigated. Comparisons with the interferometry diagnostic show a remarkable overall qualitative agreement during the discharge that can be quantitative at some locations in the plasma core. If at the onset of the X-points during the ramp-up the electron heat flux is dominant at the target, present results show that the ion heat flux becomes dominant during the stationary phase of the discharge. Using a simple model for erosion, present results assess the tungsten sputtering due to deuterium ions during the start-up and ramp-up phases of the discharge and confirms the need to consider full discharge simulation to accurately treat the W source of contamination. This work also demonstrates the interest of developing magnetic equilibrium free solver including efficient time integration to step toward predictive capabilities in the future for fusion operation.
M Scotto d'Abusco, G Giorgiani, J F Artaud, H Bufferand, G Ciraolo, et al.. Core-edge 2D fluid modeling of full tokamak discharge with varying magnetic equilibrium: from WEST start-up to ramp-down. Nuclear Fusion, 2022, ⟨10.1088/1741-4326/ac47ad⟩. ⟨hal-03509800⟩
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir-Computing-Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , In press. ⟨hal-03200715v2⟩ Plus de détails...
A detailed parametric analysis is presented, where the recent method based on the Reservoir Computing paradigm, including its statistical robustness, is studied. It is observed that the prediction capabilities of the Reservoir Computing approach strongly depend on the random initialisation of both the input and the reservoir layers. Special emphasis is put on finding the region in the hyperparameter space where the ensemble-averaged training and generalization errors together with their variance are minimized. The statistical analysis presented here is based on the Projection on Proper Elements (PoPe) method [T. Cartier-Michaud et al., Phys. Plasmas 23, 020702 (2016)].
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir-Computing-Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , In press. ⟨hal-03200715v2⟩
Giacomo Piraccini, Marcello Capasso, Manuel Scotto d'Abusco, Giorgio Giorgiani, Frédéric Schwander, et al.. Recent upgrades in a 2D turbulent transport solver based on a hybrid discontinuous Galerkin method for the simulation of fusion plasma in tokamak. Fluids, 2022, ⟨10.3390/fluids7020063⟩. ⟨hal-03562497⟩ Plus de détails...
The simulation of fusion plasmas in realistic magnetic configurations and tokamak ge-1 ometries still requires the development of advanced numerical algorithms owing to the complexity 2 of the problem. In this context, we propose a Hybrid Discontinuous Galerkin (HDG) method to 3 solve 2D transport fluid equations in realistic magnetic and tokamak wall geometries. This high-4 order solver can handle magnetic equilibrium free structured and unstructured meshes allowing a 5 much more accurate discretization of the plasma facing components than current solvers based 6 on magnetic field aligned methods associated to finite-differences (volumes) discretization. In 7 addition, the method allows to handle realistic magnetic equilibrium, eventually non steady, a 8 critical point in the modelling of full discharges including ramp up and ramp down phases. In 9 this paper, we introduce the HDG algorithm with a special focus on recent developments related 10 to the treatment of the cross-field diffusive terms, and to an adaptive mesh refinement technique 11 improving the numerical efficiency and robustness of the scheme. The updated solver is verified 12 with a manufactured solution method, and numerical tests are provided to illustrate the new 13 capabilities of the code.
Giacomo Piraccini, Marcello Capasso, Manuel Scotto d'Abusco, Giorgio Giorgiani, Frédéric Schwander, et al.. Recent upgrades in a 2D turbulent transport solver based on a hybrid discontinuous Galerkin method for the simulation of fusion plasma in tokamak. Fluids, 2022, ⟨10.3390/fluids7020063⟩. ⟨hal-03562497⟩
Gauthier Wissocq, Thomas Coratger, Gabriel Farag, Song Zhao, Pierre Boivin, et al.. Restoring the conservativity of characteristic-based segregated models: application to the hybrid lattice Boltzmann method. Physics of Fluids, 2022, 34 (4), pp.046102. ⟨10.1063/5.0083377⟩. ⟨hal-03627520⟩ Plus de détails...
A general methodology is introduced to build conservative numerical models for fluid simulations based on segregated schemes, where mass, momentum and energy equations are solved by different methods. It is here especially designed for developing new numerical discretizations of the total energy equation, adapted to a thermal coupling with the lattice Boltzmann method (LBM). The proposed methodology is based on a linear equivalence with standard discretizations of the entropy equation, which, as a characteristic variable of the Euler system, allows efficiently decoupling the energy equation with the LBM. To this extent, any LBM scheme is equivalently written under a finite-volume formulation involving fluxes, which are further included in the total energy equation as numerical corrections. The viscous heat production is implicitly considered thanks to the knowledge of the LBM momentum flux. Three models are subsequently derived: a first-order upwind, a Lax-Wendroff and a third-order Godunov-type schemes. They are assessed on standard academic test cases: a Couette flow, entropy spot and vortex convections, a Sod shock tube, several two-dimensional Riemann problems and a shock-vortex interaction. Three key features are then exhibited: 1) the models are conservative by construction, recovering correct jump relations across shock waves, 2) the stability and accuracy of entropy modes can be explicitly controlled, 3) the low dissipation of the LBM for isentropic phenomena is preserved.
Gauthier Wissocq, Thomas Coratger, Gabriel Farag, Song Zhao, Pierre Boivin, et al.. Restoring the conservativity of characteristic-based segregated models: application to the hybrid lattice Boltzmann method. Physics of Fluids, 2022, 34 (4), pp.046102. ⟨10.1063/5.0083377⟩. ⟨hal-03627520⟩
D.S. Oliveira, T. Body, D. Galassi, C. Theiler, E. Laribi, et al.. Validation of edge turbulence codes against the TCV-X21 diverted L-mode reference case. Nuclear Fusion, 2022, 62 (9), pp.096001. ⟨10.1088/1741-4326/ac4cde⟩. ⟨hal-03740877⟩ Plus de détails...
Self-consistent full-size turbulent-transport simulations of the divertor and scrape-off-layer (SOL) of existing tokamaks have recently become feasible. This enables the direct comparison of turbulence simulations against experimental measurements. In this work, we perform a series of diverted ohmic L-mode discharges on the tokamak à configuration variable (TCV) tokamak, building a first-of-a-kind dataset for the validation of edge turbulence models. This dataset, referred to as TCV-X21 , contains measurements from five diagnostic systems from the outboard midplane (OMP) to the divertor targets—giving a total of 45 one- and two-dimensional comparison observables in two toroidal magnetic field directions. The experimental dataset is used to validate three flux-driven 3D fluid-turbulence models—GBS, GRILLIX and TOKAM3X. With each model, we perform simulations of the TCV-X21 scenario, individually tuning the particle and power source rates to achieve a reasonable match of the upstream separatrix value of density and electron temperature. We find that the simulations match the experimental profiles for most observables at the OMP—both in terms of profile shape and absolute magnitude—while a comparatively poorer agreement is found towards the divertor targets. The match between simulation and experiment is seen to be sensitive to the value of the resistivity, the heat conductivities, the power injection rate and the choice of sheath boundary conditions. Additionally, despite targeting a sheath-limited regime, the discrepancy between simulations and experiment also suggests that the neutral dynamics should be included. The results of this validation show that turbulence models are able to perform simulations of existing devices and achieve reasonable agreement with experimental measurements. Where disagreement is found, the validation helps to identify how the models can be improved. By publicly releasing the experimental dataset and validation analysis, this work should help to guide and accelerate the development of predictive turbulence simulations of the edge and SOL.
D.S. Oliveira, T. Body, D. Galassi, C. Theiler, E. Laribi, et al.. Validation of edge turbulence codes against the TCV-X21 diverted L-mode reference case. Nuclear Fusion, 2022, 62 (9), pp.096001. ⟨10.1088/1741-4326/ac4cde⟩. ⟨hal-03740877⟩
Guanxiong Wang, Song Zhao, Pierre Boivin, Eric Serre, Pierre Sagaut. A new hybrid Lattice-Boltzmann method for thermal flow simulations in low-Mach number approximation. Physics of Fluids, 2022, Physics of fluids, 34 (046114). ⟨hal-03636905⟩ Plus de détails...
Guanxiong Wang, Song Zhao, Pierre Boivin, Eric Serre, Pierre Sagaut. A new hybrid Lattice-Boltzmann method for thermal flow simulations in low-Mach number approximation. Physics of Fluids, 2022, Physics of fluids, 34 (046114). ⟨hal-03636905⟩
Giacomo Piraccini, Frédéric Schwander, Eric Serre, Giorgio Giorgiani, Manuel Scotto D’abusco. Spatial adaptivity in SOLEDGE3X‐HDG for edge plasma simulations in versatile magnetic and reactor geometries. Contributions to Plasma Physics, 2022, 18th International Workshop on Plasma Edge Theory in Fusion Devices September 13‐15, 2021, organized by the EPFL Swiss Plasma Center, 62 (5-6), ⟨10.1002/ctpp.202100185⟩. ⟨hal-04489377⟩ Plus de détails...
With the ultimate goal to predict plasmas heat and particle fluxes in ITER operation, more efforts are required to deal with realistic magnetic configurations and tokamak geometries. In an attempt to achieve this goal, we propose an adaptive mesh refinement method added to a fluid solver based on a high‐order hybrid discontinuous Galerkin (HDG) method. Based on unstructured meshes, this magnetic equilibrium free numerical scheme has shown promising and encouraging features to solve 2D/3D transport reduced Braginski fluid equations. To improve its numerical efficiency, a mesh refinement based on h‐adpativity is investigated. We describe here an adaptive refinement strategy on a reduced edge particle transport model based on electron density and parallel momentum. This strategy is illustrated in realistic tokamak wall geometry. Computations performed show potential gains in the required number of degrees of freedom against benchmark computations with uniform meshes, along with the potential to give an automated, goal‐oriented, mesh generation technique for edge transport simulations in 2D.
Giacomo Piraccini, Frédéric Schwander, Eric Serre, Giorgio Giorgiani, Manuel Scotto D’abusco. Spatial adaptivity in SOLEDGE3X‐HDG for edge plasma simulations in versatile magnetic and reactor geometries. Contributions to Plasma Physics, 2022, 18th International Workshop on Plasma Edge Theory in Fusion Devices September 13‐15, 2021, organized by the EPFL Swiss Plasma Center, 62 (5-6), ⟨10.1002/ctpp.202100185⟩. ⟨hal-04489377⟩
Lincheng Xu, Eric Serre, Pierre Sagaut. A theoretical analysis of mass leakage at boundaries within the lattice Boltzmann method. Physics of Fluids, 2022, Physics of fluids, 34 (065113). ⟨hal-03683744⟩ Plus de détails...
Mass leakage at boundaries can be a critical issue for reliability of the lattice Boltzmann (LB) method based on Cartesian grids. Despite numerous work based on the LB method, the intrinsic macroscopic mechanisms causing mass leakage are still not fully charac- terised, but are essential to improve the mass conservation of LB simulations. In this paper, an original theoretical investigation of mass leakage at boundaries is proposed within the general LB framework. It is demonstrated that the mass leakage originates from the in- trinsic deficiency of the wall-cut LB links at boundary nodes in recovering macroscopic momenta. From a mesoscopic-level definition, i.e. the net loss of distribution functions during the streaming process, the local mass leakage at individual boundary nodes and its averaged value along smooth boundaries are mathematically expressed using macroscopic variables. The local mass leakage is shown to be dominated by terms proportional to the tangential momentum component. In contrast, the averaged mass leakage is shown to be contributed from various terms including the boundary curvature, the tangential momen- tum, and the gradients of density, momentum and momentum flux. Meanwhile, amplitude of the averaged mass leakage is theoretically estimated to be proportional to the local grid spacing, based on which a first-order accurate correction scheme is proposed. In addition, both the local and averaged mass leakage are demonstrated to be significantly dependent on boundary orientation with respect to the grid. The proposed theoretical analysis is assessed by performing numerical experiments. Two-dimensional weakly compressible flows through straight and curved moving channels are considered to estimate each term appearing in the theoretical analysis. The numerical results are in very good agreement with the proposed analysis, and the proposed mass correction scheme based on the av- eraged mass leakage effectively cures the mass leakage problems in the considered test cases.
Lincheng Xu, Eric Serre, Pierre Sagaut. A theoretical analysis of mass leakage at boundaries within the lattice Boltzmann method. Physics of Fluids, 2022, Physics of fluids, 34 (065113). ⟨hal-03683744⟩
Thomas Astoul, Gauthier Wissocq, Jean-François Boussuge, Alois Sengissen, Pierre Sagaut. Lattice Boltzmann method for computational aeroacoustics on non-uniform meshes: A direct grid coupling approach. Journal of Computational Physics, 2021, 447, pp.110667. ⟨10.1016/j.jcp.2021.110667⟩. ⟨hal-03514616⟩ Plus de détails...
The present study proposes an accurate lattice Boltzmann direct coupling algorithm, well suited for industrial purposes, making it highly valuable for aeroacoustic applications. It is indeed known that the convection of vortical structures across a grid refinement interface, where cell size is abruptly doubled, is likely to generate spurious noise that may corrupt the solution over the whole computational domain. This issue becomes critical in the case of aeroacoustic simulations, where accurate pressure estimations are of paramount importance. Consequently, any interfering noise that may pollute the acoustic predictions must be reduced. The proposed grid refinement algorithm differs from conventionally used ones, in which an overlapping mesh layer is considered. Instead, it provides a direct connection allowing a tighter link between fine and coarse grids, especially with the use of a coherent equilibrium function shared by both grids. Moreover, the direct coupling makes the algorithm more local and prevents the duplication of points, which might be detrimental for massive parallelization. This work follows our first study (Astoul et al. 2020 [1]) on the deleterious effect of non-hydrodynamic modes crossing mesh transitions, which can be addressed using an appropriate collision model: the hybrid recursive regularization. The grid coupling algorithm is assessed in the context of computational aeroacoustics and compared to a widely-used cell-vertex algorithm. The validation benchmark includes the simulation of (1) an acoustic pulse, (2) a vortex transport by a mean flow, and finally, (3) a turbulent circular cylinder wake flow at high Reynolds number. In the end, the proposed approach is proven to drastically reduced the spurious noise generated at grid interfaces, hence, paving the way for accurate and efficient aeroacoustic simulations based on lattice Boltzmann methods. (C) 2021 Elsevier Inc. All rights reserved.
Thomas Astoul, Gauthier Wissocq, Jean-François Boussuge, Alois Sengissen, Pierre Sagaut. Lattice Boltzmann method for computational aeroacoustics on non-uniform meshes: A direct grid coupling approach. Journal of Computational Physics, 2021, 447, pp.110667. ⟨10.1016/j.jcp.2021.110667⟩. ⟨hal-03514616⟩
Florian Renard, Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. A linear stability analysis of compressible hybrid lattice Boltzmann methods. Journal of Computational Physics, 2021, 446, pp.110649. ⟨10.1016/j.jcp.2021.110649⟩. ⟨hal-03514639⟩ Plus de détails...
An original spectral study of the compressible hybrid lattice Boltzmann method (HLBM) on standard lattice is proposed. In this framework, the mass and momentum equations are addressed using the lattice Boltzmann method (LBM), while finite difference (FD) schemes solve an energy equation. Both systems are coupled with each other thanks to an ideal gas equation of state. This work aims at answering some questions regarding the numerical stability of such models, which strongly depends on the choice of numerical parameters. To this extent, several one- and two-dimensional HLBM classes based on different energy variables, formulations (primitive or conservative), collision terms and numerical schemes are scrutinized. Once appropriate corrective terms introduced, it is shown that all continuous HLBM classes recover the Navier-Stokes-Fourier behavior in the linear approximation. However, striking differences arise between HLBM classes when their discrete counterparts are analyzed. Multiple instability mechanisms arising at relatively high Mach number are pointed out and two exhaustive stabilization strategies are introduced: (1) decreasing the time step by changing the reference temperature T-r and (2) introducing a controllable numerical dissipation a via the collision operator. A complete parametric study reveals that only HLBM classes based on the primitive and conservative entropy equations are found usable for compressible applications. Finally, an innovative study of the macroscopic modal composition of the entropy classes is conducted. Through this study, two original phenomena, referred to as shear-to-entropy and entropy-to-shear transfers, are highlighted and confirmed on standard two-dimensional test cases. (C) 2021 Elsevier Inc. All rights reserved.
Florian Renard, Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. A linear stability analysis of compressible hybrid lattice Boltzmann methods. Journal of Computational Physics, 2021, 446, pp.110649. ⟨10.1016/j.jcp.2021.110649⟩. ⟨hal-03514639⟩
T. Coratger, G. Farag, S. Zhao, Pierre Boivin, P. Sagaut. Large-eddy lattice-Boltzmann modeling of transonic flows. Physics of Fluids, 2021, 33 (11), pp.115112. ⟨10.1063/5.0064944⟩. ⟨hal-03424286⟩ Plus de détails...
T. Coratger, G. Farag, S. Zhao, Pierre Boivin, P. Sagaut. Large-eddy lattice-Boltzmann modeling of transonic flows. Physics of Fluids, 2021, 33 (11), pp.115112. ⟨10.1063/5.0064944⟩. ⟨hal-03424286⟩
Guanxiong Wang, Lincheng Xu, Eric Serre, Pierre Sagaut. Large temperature difference heat dominated flow simulations using a pressure-based lattice Boltzmann method with mass correction. Physics of Fluids, 2021, 33 (11), pp.116107. ⟨10.1063/5.0073178⟩. ⟨hal-03438869⟩ Plus de détails...
This paper addresses simulation of heat dominated compressible flows in a closed cavity using a pressure-based lattice Boltzmann (LB) method, in which thermal effects are modeled by applying a pressure-featured zero-order moment of distribution functions. A focus is made on the conservation of mass at boundary nodes, which is a challenging issue that significantly complicated by the density-decoupled zero-order moment here. The mass leakage at boundary nodes is mathematically quantified, which enables an efficient local mass correction scheme. The performance of this solver is assessed by simulating buoyancy-driven flows in a closed deferentially heated cavity with large temperature differences (non-Boussinesq) at Rayleigh numbers ranging from 103 to 107. Simulations show that mass leakage at solid walls in such configurations is a critical issue to obtain reliable solutions, and it eventually leads to simulations overflow when the cavity is inclined. The proposed mass correction scheme is, however, shown to be effective to control the mass leakage and get accurate solutions. Thus, associated with the proposed mass conservation scheme, the pressure-based LB method becomes reliable to study natural convection dominated flows at large temperature differences in closed geometries with mesh aligned boundaries or not
Guanxiong Wang, Lincheng Xu, Eric Serre, Pierre Sagaut. Large temperature difference heat dominated flow simulations using a pressure-based lattice Boltzmann method with mass correction. Physics of Fluids, 2021, 33 (11), pp.116107. ⟨10.1063/5.0073178⟩. ⟨hal-03438869⟩
Felix Marlow, Jérôme Jacob, Pierre Sagaut. A multidisciplinary model coupling Lattice-Boltzmann-based CFD and a Social Force Model for the simulation of pollutant dispersion in evacuation situations. Building and Environment, 2021, 205, pp.108212. ⟨10.1016/j.buildenv.2021.108212⟩. ⟨hal-03514660⟩ Plus de détails...
In closed rooms with limited convection human motion can considerably affect the airflow and thus the dispersion of pollutant. However, in Computational Fluid Dynamics (CFD) simulations on air quality and safety for human beings this effect is generally not considered, which is mainly due to a lack of a well-founded and detailed estimation of the human behavior and the high computational cost of taking into account moving objects in CFD meshes. This work addresses this issue by coupling multidisciplinary methods to allow for a more realistic simulation of pollutant dispersion by taking into account the influence of human movements. A Social Force Model predicts trajectory and speed of each person moving in a complex environment. A lattice Boltzmann-based CFD tool provides a Large Eddy Simulation of the unsteady turbulent airflow with pollutant dispersion and thermal effects. And an Actuator Line Model supplies the CFD tool with body forces that mimic the impact of moving objects on the airflow, thus, avoiding computationally expensive dynamic meshing. The capability of the coupled model is demonstrated on three realistic evacuation scenarios with various pollutant sources and a wide range of scales (dimension from 10 to 100 m, occupation from 10 to 6000 persons). The results allow to access instantaneous environmental parameters like pollutant concentration for each person during the course of the evacuation, enabling the assessment of associated health risks.
Felix Marlow, Jérôme Jacob, Pierre Sagaut. A multidisciplinary model coupling Lattice-Boltzmann-based CFD and a Social Force Model for the simulation of pollutant dispersion in evacuation situations. Building and Environment, 2021, 205, pp.108212. ⟨10.1016/j.buildenv.2021.108212⟩. ⟨hal-03514660⟩
Felix Marlow, Jérôme Jacob, Pierre Sagaut. A multidisciplinary model coupling Lattice-Boltzmann-based CFD and a Social Force Model for the simulation of pollutant dispersion in evacuation situations. Building and Environment, 2021, 205, pp.108212. ⟨10.1016/j.buildenv.2021.108212⟩. ⟨hal-03597658⟩ Plus de détails...
In closed rooms with limited convection human motion can considerably affect the airflow and thus the dispersion of pollutant. However, in Computational Fluid Dynamics (CFD) simulations on air quality and safety for human beings this effect is generally not considered, which is mainly due to a lack of a well-founded and detailed estimation of the human behavior and the high computational cost of taking into account moving objects in CFD meshes. This work addresses this issue by coupling multidisciplinary methods to allow for a more realistic simulation of pollutant dispersion by taking into account the influence of human movements. A Social Force Model predicts trajectory and speed of each person moving in a complex environment. A lattice Boltzmann-based CFD tool provides a Large Eddy Simulation of the unsteady turbulent airflow with pollutant dispersion and thermal effects. And an Actuator Line Model supplies the CFD tool with body forces that mimic the impact of moving objects on the airflow, thus, avoiding computationally expensive dynamic meshing. The capability of the coupled model is demonstrated on three realistic evacuation scenarios with various pollutant sources and a wide range of scales (dimension from 10 to 100 m, occupation from 10 to 6000 persons). The results allow to access instantaneous environmental parameters like pollutant concentration for each person during the course of the evacuation, enabling the assessment of associated health risks.
Felix Marlow, Jérôme Jacob, Pierre Sagaut. A multidisciplinary model coupling Lattice-Boltzmann-based CFD and a Social Force Model for the simulation of pollutant dispersion in evacuation situations. Building and Environment, 2021, 205, pp.108212. ⟨10.1016/j.buildenv.2021.108212⟩. ⟨hal-03597658⟩
H. Bufferand, J. Bucalossi, G. Ciraolo, G. Falchetto, A. Gallo, et al.. Progress in edge plasma turbulence modelling hierarchy of models from 2D transport application to 3D fluid simulations in realistic tokamak geometry. Nuclear Fusion, 2021, 61 (11), pp.116052. ⟨10.1088/1741-4326/ac2873⟩. ⟨hal-03377162⟩ Plus de détails...
This contribution presents the recent effort at CEA and French federation for Fusion to simulate edge plasma transport with the new code SOLEDGE3X. The latter can be used both as a 2D transport code or as a 3D turbulence code. It makes possible simulating edge plasma up to the first wall including the complex wall geometry. It also includes neutral recycling and impurity sputtering, seeding and transport. In order to improve turbulence description in transport simulation, a reduced model for turbulence intensity prediction has been derived and implemented, based on "kepsilon" like models from the neutral fluid community. Applications to a JET L-mode detached plasma and to a WEST plasma are used as illustration of the code abilities
H. Bufferand, J. Bucalossi, G. Ciraolo, G. Falchetto, A. Gallo, et al.. Progress in edge plasma turbulence modelling hierarchy of models from 2D transport application to 3D fluid simulations in realistic tokamak geometry. Nuclear Fusion, 2021, 61 (11), pp.116052. ⟨10.1088/1741-4326/ac2873⟩. ⟨hal-03377162⟩
Georis Billo, Michel Belliard, Pierre Sagaut. A Finite Element Penalized Direct Forcing Immersed Boundary Method for infinitely thin obstacles in a dilatable flow. Computers & Mathematics with Applications, 2021, 99, pp.292-304. ⟨10.1016/j.camwa.2021.08.005⟩. ⟨hal-03596009⟩ Plus de détails...
In the framework of the development of new passive safety systems for the second and third generations of nuclear reactors, the numerical simulations, involving complex turbulent two-phase flows around thin or massive inflow obstacles, are privileged tools to model, optimize and assess new design shapes. In order to match industrial demands, computational fluid dynamics tools must be the fastest, most accurate and most robust possible. To face this issue, we have chosen to solve the Navier-Stokes equations using a projection scheme for a mixture fluid coupled with an Immersed Boundary (IB) approach: the penalized direct forcing method-a technique whose characteristics inherit from both penalty and immersed boundary methods-adapted to infinitely thin obstacles and to a Finite Element (FE) formulation. Various IB conditions (slip, no-slip or Neumann) for the velocity on the IB can be managed by imposing Dirichlet values in the vicinity of the thin obstacles. To deal with these imposed Dirichlet velocities, we investigated two variants: one in which we use the obstacle velocity and another one in which we use linear interpolations based on discrete geometrical properties of the IB (barycenters and normal vectors) and the FE basis functions. This last variant is motivated by an increase of the accuracy/computation time ratio for coarse meshes. As a first step, concerning academic test cases for one-phase dilatable-fluid laminar flows, the results obtained via those two variants are in good agreement with analytical and experimental data. Moreover, when compared to each other, the linear interpolation variant increases the spatial order of convergence as expected. An industrial test case illustrates the advantages and drawbacks of this approach. In a shortcoming second step, to face two-phase turbulent fluid simulations, some methodology modifications will be considered such as adapting the projection scheme to low-compressible fluid and immersed wall-law boundary conditions.
Georis Billo, Michel Belliard, Pierre Sagaut. A Finite Element Penalized Direct Forcing Immersed Boundary Method for infinitely thin obstacles in a dilatable flow. Computers & Mathematics with Applications, 2021, 99, pp.292-304. ⟨10.1016/j.camwa.2021.08.005⟩. ⟨hal-03596009⟩
Journal: Computers & Mathematics with Applications
Georis Billo, Michel Belliard, Pierre Sagaut. A Finite Element Penalized Direct Forcing Immersed Boundary Method for infinitely thin obstacles in a dilatable flow. Computers & Mathematics with Applications, 2021, 99, pp.292-304. ⟨10.1016/j.camwa.2021.08.005⟩. ⟨hal-03514671⟩ Plus de détails...
In the framework of the development of new passive safety systems for the second and third generations of nuclear reactors, the numerical simulations, involving complex turbulent two-phase flows around thin or massive inflow obstacles, are privileged tools to model, optimize and assess new design shapes. In order to match industrial demands, computational fluid dynamics tools must be the fastest, most accurate and most robust possible. To face this issue, we have chosen to solve the Navier-Stokes equations using a projection scheme for a mixture fluid coupled with an Immersed Boundary (IB) approach: the penalized direct forcing method - a technique whose characteristics inherit from both penalty and immersed boundary methods - adapted to infinitely thin obstacles and to a Finite Element (FE) formulation. Various IB conditions (slip, no-slip or Neumann) for the velocity on the IB can be managed by imposing Dirichlet values in the vicinity of the thin obstacles. To deal with these imposed Dirichlet velocities, we investigated two variants: one in which we use the obstacle velocity and another one in which we use linear interpolations based on discrete geometrical properties of the IB (barycenters and normal vectors) and the FE basis functions. This last variant is motivated by an increase of the accuracy/computation time ratio for coarse meshes. As a first step, concerning academic test cases for one-phase dilatable-fluid laminar flows, the results obtained via those two variants are in good agreement with analytical and experimental data. Moreover, when compared to each other, the linear interpolation variant increases the spatial order of convergence as expected. An industrial test case illustrates the advantages and drawbacks of this approach. In a shortcoming second step, to face two-phase turbulent fluid simulations, some methodology modifications will be considered such as adapting the projection scheme to low-compressible fluid and immersed wall-law boundary conditions.
Georis Billo, Michel Belliard, Pierre Sagaut. A Finite Element Penalized Direct Forcing Immersed Boundary Method for infinitely thin obstacles in a dilatable flow. Computers & Mathematics with Applications, 2021, 99, pp.292-304. ⟨10.1016/j.camwa.2021.08.005⟩. ⟨hal-03514671⟩
Journal: Computers & Mathematics with Applications
Pierre Magnico. Molecular dynamics study on water and hydroxide transfer mechanisms in PSU-g-alkyl-TMA membranes at low hydration: Effect of side chain length. International Journal of Hydrogen Energy, 2021, 46 (68), pp.33915-33933. ⟨10.1016/j.ijhydene.2021.07.081⟩. ⟨hal-03358207⟩ Plus de détails...
Molecular dynamics simulations with anion exchange membranes (alkyl trimethyl ammonium grafted onto polysulfone) are performed to investigate the influence of the spacer length on the transport properties, on the molecular exchange mechanisms between the functional group and the aqueous phase and on the hydrogen bond network. This is especially insightful that in this work the hydration number is small. In this condition the aqueous phase must be thought as an assembly of small clusters. The results show an unexpected dependence of the water and hydroxide (OH) diffusivity on the temperature and the water uptake. The distribution of the cluster size bonded to OH explain partially the OH diffusivity. “Hopping” and “caging” motions are observed with the self-part of the Van Hove functions even at high temperature. The characteristic time of the survival probability correlation function around the functional groups is a decreasing function of the alkyl length.
Pierre Magnico. Molecular dynamics study on water and hydroxide transfer mechanisms in PSU-g-alkyl-TMA membranes at low hydration: Effect of side chain length. International Journal of Hydrogen Energy, 2021, 46 (68), pp.33915-33933. ⟨10.1016/j.ijhydene.2021.07.081⟩. ⟨hal-03358207⟩
S. Baschetti, H. Bufferand, G. Ciraolo, Ph Ghendrih, E. Serre, et al.. Self-consistent cross-field transport model for core and edge plasma transport. Nuclear Fusion, 2021, 61 (10), pp.106020. ⟨10.1088/1741-4326/ac1e60⟩. ⟨hal-03380310⟩ Plus de détails...
A two-equation model to self-consistently determine cross-field fluxes in the edge and scrape-off layer region of diverted plasma is used to complete 2D mean-field edge transport description of plasma wall interaction. Inspired by the Reynolds Average Navier-Stokes simulations for neutral fluids, this model is based on the local evolution of the turbulent kinetic energy κ and its dissipation rate ε. These two equations are algebraically derived for RANS modeling and are very slightly modified and adapted to describe self-consistent plasma turbulent transport. The general features of the model are discussed and bridged to the well-known predatorprey and quasilinear models commonly used to investigate plasma transport. Specific closures are proposed based on the interchange turbulence. Results of the 1D model are confronted to experimental evidence by analyzing the computed SOL width and comparing the results to the existing scaling law for L-mode plasmas. Introducing a dependence on the shear of large scale flows, typically the zonal flows, 1D simulations can exhibit an H-mode like transition when increasing the input power, generating an increased stored energy thanks to an interface barrier located at the separatrix. Further 2D plasma-wall interaction simulations for WEST are analyzed that show a good match with the experimental profiles, as well as a ballooned transport driving turbulent transport in the divertor SOL and nearly no transport in the private flux region. The SOL width of WEST is also recovered. These results show the remarkable capability of the κ-ε model to capture key aspects of the physics of turbulent transport throughout the plasma knowing that a unique scalar free parameter is available to tune cross field transport in the whole 2D cross section of the plasma.
S. Baschetti, H. Bufferand, G. Ciraolo, Ph Ghendrih, E. Serre, et al.. Self-consistent cross-field transport model for core and edge plasma transport. Nuclear Fusion, 2021, 61 (10), pp.106020. ⟨10.1088/1741-4326/ac1e60⟩. ⟨hal-03380310⟩
S. Di Genova, A. Gallo, N. Fedorczak, H. Yang, G. Ciraolo, et al.. Modelling of tungsten contamination and screening in WEST plasma discharges. Nuclear Fusion, 2021, 61 (10), pp.106019. ⟨10.1088/1741-4326/ac2026⟩. ⟨hal-03380329⟩ Plus de détails...
The WEST experiment is currently operating with tungsten plasma-facing components and testing ITER-like divertor monoblocks. In order to support WEST experiments interpretation, numerical analyses were carried out. Starting from WEST experimental data, realistic background plasma conditions were reproduced through SolEdge-EIRENE and used as input for ERO2.0 simulations to investigate tungsten migration. Tungsten contamination due to the different plasma-facing components was modelled under different plasma conditions, highlighting a non-negligible contribution of tungsten coming from the tokamak main chamber. Tungsten penetration factor was computed and used as an indication for tungsten screening by the background plasma at the different tokamak plasma-facing components. Simulations showed the main chamber components to be very weakly screened. Light impurities charge was showed to influence not only tungsten sputtering, but also its probability to enter the confined plasma. Simulations results indicated that even when the tungsten source is not heavily influenced by self-sputtering, contamination of the confined plasma can be strongly impacted by it in low density background plasma conditions. Finally, a one-to-one comparison between tungsten visible spectroscopy at the lower divertor from experimental data and from synthetic diagnostics was performed, showing that it is possible to reproduce a realistic lower divertor signal following experimental evidence on light impurities asymmetry between the targets.
S. Di Genova, A. Gallo, N. Fedorczak, H. Yang, G. Ciraolo, et al.. Modelling of tungsten contamination and screening in WEST plasma discharges. Nuclear Fusion, 2021, 61 (10), pp.106019. ⟨10.1088/1741-4326/ac2026⟩. ⟨hal-03380329⟩
Johan Degrigny, Shang-Gui Cai, Jean-François Boussuge, Pierre Sagaut. Improved wall model treatment for aerodynamic flows in LBM. Computers and Fluids, 2021, 227, pp.105041. ⟨10.1016/j.compfluid.2021.105041⟩. ⟨hal-03326170⟩ Plus de détails...
The article deals with an improved treatment of wall models for the simulation of turbulent flows in the framework of Immersed Wall Boundaries on Cartesian grids. The emphasis is put on the implementa-tion in a Lattice-Boltzmann Method solver without loss of generality, since the proposed approach can be used in Navier-Stokes-based solvers in a straightforward way. The proposed improved wall model im-plementation relies on the combination of several key elements, namely i) the removal of grid points too close to the solid surface and ii) an original computation of wall normal velocity gradient and iii) the interpolation scheme. The new method is successfully assessed considering URANS simulations focusing on steady solutions of the Zero Pressure Gradient turbulent flat plate boundary layer and the turbulent flow around a NACA0012 airfoil at several angles of attack.
Johan Degrigny, Shang-Gui Cai, Jean-François Boussuge, Pierre Sagaut. Improved wall model treatment for aerodynamic flows in LBM. Computers and Fluids, 2021, 227, pp.105041. ⟨10.1016/j.compfluid.2021.105041⟩. ⟨hal-03326170⟩
Isabelle Cheylan, Julien Favier, Pierre Sagaut. Immersed boundary conditions for moving objects in turbulent flows with the lattice-Boltzmann method. Physics of Fluids, 2021, 33 (9), pp.095101. ⟨10.1063/5.0062575⟩. ⟨hal-03514710⟩ Plus de détails...
An immersed boundary method is coupled to a turbulent wall model and Large Eddy Simulation, within the Lattice-Boltzmann framework. The method is able to handle arbitrarily moving objects immersed in a high Reynolds number flow and to accurately capture the shear layer and near wall effects. We perform a thorough numerical study which validates the numerical method on a set of test-cases of increasing complexity, in order to demonstrate the application of this method to industrial conditions. The robustness and accuracy of the method are assessed first in a static laminar configuration, then in a mobile laminar case, and finally in a static and oscillating turbulent simulation. In all cases, the proposed method shows good results compared to the available data in the literature.
Isabelle Cheylan, Julien Favier, Pierre Sagaut. Immersed boundary conditions for moving objects in turbulent flows with the lattice-Boltzmann method. Physics of Fluids, 2021, 33 (9), pp.095101. ⟨10.1063/5.0062575⟩. ⟨hal-03514710⟩
Isabelle Cheylan, Julien Favier, Pierre Sagaut. Immersed boundary conditions for moving objects in turbulent flows with the lattice-Boltzmann method. Physics of Fluids, 2021, 33 (9), pp.095101. ⟨10.1063/5.0062575⟩. ⟨hal-03597108⟩ Plus de détails...
An immersed boundary method is coupled to a turbulent wall model and Large Eddy Simulation, within the Lattice-Boltzmann framework. The method is able to handle arbitrarily moving objects immersed in a high Reynolds number flow and to accurately capture the shear layer and near wall effects. We perform a thorough numerical study which validates the numerical method on a set of test-cases of increasing complexity, in order to demonstrate the application of this method to industrial conditions. The robustness and accuracy of the method are assessed first in a static laminar configuration, then in a mobile laminar case, and finally in a static and oscillating turbulent simulation. In all cases, the proposed method shows good results compared to the available data in the literature.
Isabelle Cheylan, Julien Favier, Pierre Sagaut. Immersed boundary conditions for moving objects in turbulent flows with the lattice-Boltzmann method. Physics of Fluids, 2021, 33 (9), pp.095101. ⟨10.1063/5.0062575⟩. ⟨hal-03597108⟩
M Raghunathan, Y Marandet, H Bufferand, G Ciraolo, Ph Ghendrih, et al.. Generalized Collisional Fluid Theory for Multi-Component, Multi-Temperature Plasma Using The Linearized Boltzmann Collision Operator for Scrape-Off Layer/Edge Applications. Plasma Physics and Controlled Fusion, 2021, 63 (6), pp.064005. ⟨10.1088/1361-6587/abf670⟩. ⟨hal-03384547⟩ Plus de détails...
M Raghunathan, Y Marandet, H Bufferand, G Ciraolo, Ph Ghendrih, et al.. Generalized Collisional Fluid Theory for Multi-Component, Multi-Temperature Plasma Using The Linearized Boltzmann Collision Operator for Scrape-Off Layer/Edge Applications. Plasma Physics and Controlled Fusion, 2021, 63 (6), pp.064005. ⟨10.1088/1361-6587/abf670⟩. ⟨hal-03384547⟩
Elisa Buffa, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann-based large-eddy simulation of high-rise building aerodynamics with inlet turbulence reconstruction. Journal of Wind Engineering and Industrial Aerodynamics, 2021, 212, pp.104560. ⟨10.1016/j.jweia.2021.104560⟩. ⟨hal-03596056⟩ Plus de détails...
Boltzmann-based Large-Eddy Simulation approach for wind load prediction on high-rise building is proposed and validated. An extension of the original incompressible Synthetic Eddy Method to reconstruct inlet turbulence is proposed within the Lattice-Boltzmann framework, including a low-noise frozen density variant. Extensive successful comparisons with experimental data are carried out, for both quantities defined on the building surface and in its wake. A detailed sensitivity analysis of the results with respect to inlet turbulence reconstruction, boundary conditions at the building surface and grid resolution is also provided. An almost unique set of comparisons with experimental data is presented, including mean and rms values, spectra, but also peak values of pressure at the building surface.
Elisa Buffa, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann-based large-eddy simulation of high-rise building aerodynamics with inlet turbulence reconstruction. Journal of Wind Engineering and Industrial Aerodynamics, 2021, 212, pp.104560. ⟨10.1016/j.jweia.2021.104560⟩. ⟨hal-03596056⟩
Journal: Journal of Wind Engineering and Industrial Aerodynamics
H. Yoo, M. Bahlali, Julien Favier, Pierre Sagaut. A hybrid recursive regularized lattice Boltzmann model with overset grids for rotating geometries. Physics of Fluids, 2021, 33 (5), pp.057113. ⟨10.1063/5.0045524⟩. ⟨hal-03597721⟩ Plus de détails...
Simulating rotating geometries in fluid flows for industrial applications remains a challenging task for general fluid solvers and in particular for the lattice Boltzmann method (LBM) due to inherent stability and accuracy problems. This work proposes an original method based on the widely used overset grids (or Chimera grids) while being integrated with a recent and optimized LBM collision operator, the hybrid recursive regularized model (HRR). The overset grids are used to actualize the rotating geometries where both the rotating and fixed meshes exist simultaneously. In the rotating mesh, the fictitious forces generated from its non-inertial rotating reference frame are taken into account by using a second order discrete forcing term. The fixed and rotating grids communicate with each other through the interpolation of the macroscopic variables. Meanwhile, the HRR collision model is selected to enhance the stability and accuracy properties of the LBM simulations by filtering out redundant higher order non-equilibrium tensors. The robustness of the overset HRR algorithm is assessed on different configurations, undergoing mid-to-high Reynolds number flows, and the method successfully demonstrates its robustness while exhibiting the second order accuracy.
H. Yoo, M. Bahlali, Julien Favier, Pierre Sagaut. A hybrid recursive regularized lattice Boltzmann model with overset grids for rotating geometries. Physics of Fluids, 2021, 33 (5), pp.057113. ⟨10.1063/5.0045524⟩. ⟨hal-03597721⟩
H. Yoo, M. Bahlali, Julien Favier, Pierre Sagaut. A hybrid recursive regularized lattice Boltzmann model with overset grids for rotating geometries. Physics of Fluids, 2021, 33 (5), pp.057113. ⟨10.1063/5.0045524⟩. ⟨hal-03326134⟩ Plus de détails...
Simulating rotating geometries in fluid flows for industrial applications remains a challenging task for general fluid solvers and in particular for the lattice Boltzmann method (LBM) due to inherent stability and accuracy problems. This work proposes an original method based on the widely used overset grids (or Chimera grids) while being integrated with a recent and optimized LBM collision operator, the hybrid recursive regularized model (HRR). The overset grids are used to actualize the rotating geometries where both the rotating and fixed meshes exist simultaneously. In the rotating mesh, the fictitious forces generated from its non-inertial rotating reference frame are taken into account by using a second order discrete forcing term. The fixed and rotating grids communicate with each other through the interpolation of the macroscopic variables. Meanwhile, the HRR collision model is selected to enhance the stability and accuracy properties of the LBM simulations by filtering out redundant higher order non-equilibrium tensors. The robustness of the overset HRR algorithm is assessed on different configurations, undergoing mid-to-high Reynolds number flows, and the method successfully demonstrates its robustness while exhibiting the second order accuracy.
H. Yoo, M. Bahlali, Julien Favier, Pierre Sagaut. A hybrid recursive regularized lattice Boltzmann model with overset grids for rotating geometries. Physics of Fluids, 2021, 33 (5), pp.057113. ⟨10.1063/5.0045524⟩. ⟨hal-03326134⟩
M. Bahlali, H. Yoo, Julien Favier, Pierre Sagaut. A lattice Boltzmann direct coupling overset approach for the moving boundary problem. Physics of Fluids, 2021, 33 (5), pp.053607. ⟨10.1063/5.0044994⟩. ⟨hal-03326151⟩ Plus de détails...
We propose a new direct coupling scheme based on the overset technique to tackle moving boundary problems within the lattice Boltzmann framework. The scheme is based on the interpolation of distribution functions rather than moments, that is, macroscopic variables, and includes an additional hypothesis ensuring mass and momentum conservation at the interface nodes between fixed and moving grids. The method is assessed considering four test cases and considering both the vortical and the acoustic fields. It is shown that the direct coupling method results are in very good agreement with reference results on a configuration without any moving subdomain. Moreover, it is demonstrated that the direct coupling method provides an improvement of the accuracy of the lattice Boltzmann overset algorithm for aeroacoustics. In particular, a convected vortex test case is studied and reveals that the direct coupling approach leads to a better ability to conserve the vortex structure over time, as well as a reduction in spurious acoustic distorsions at the fixed/moving interface.
M. Bahlali, H. Yoo, Julien Favier, Pierre Sagaut. A lattice Boltzmann direct coupling overset approach for the moving boundary problem. Physics of Fluids, 2021, 33 (5), pp.053607. ⟨10.1063/5.0044994⟩. ⟨hal-03326151⟩
Shang-Gui Cai, Pierre Sagaut. Explicit wall models for large eddy simulation. Physics of Fluids, 2021, 33 (4), pp.041703. ⟨10.1063/5.0048563⟩. ⟨hal-03597083⟩ Plus de détails...
Algebraic explicit wall models covering the entire inner region of the turbulent boundary layer are proposed to reduce the computational effort for large eddy simulation of wall-bounded turbulent flows. The proposed formulas are given in closed forms with either logarithmicor power-function-based laws of the wall, allowing straightforward evaluation of the friction velocity on near wall grids independent of their locations in the turbulent boundary layer. The performance of the proposed models is demonstrated by the wall modeled large eddy simulation of a turbulent plane channel flow.
Shang-Gui Cai, Pierre Sagaut. Explicit wall models for large eddy simulation. Physics of Fluids, 2021, 33 (4), pp.041703. ⟨10.1063/5.0048563⟩. ⟨hal-03597083⟩
Jérémie Janin, Fabien Duval, Christophe Friess, Pierre Sagaut. A new linear forcing method for isotropic turbulence with controlled integral length scale. Physics of Fluids, 2021, 33 (4), pp.045127. ⟨10.1063/5.0045818⟩. ⟨hal-03326165⟩ Plus de détails...
Turbulence is a common feature to all flows that surround us. Despite its ubiquity, particularly in industrial flows, it is very difficult to provide a mathematical framework to the generation of turbulent eddies. Several techniques have been proposed which are able to reproduce the main features of turbulent flows, such as realistic pressure and velocity fluctuations, exhibiting proper space- and time-correlations. These techniques are usually first evaluated upon sustained homogeneous isotropic turbulence by introducing body forces to the Navier-Stokes equations. Among these techniques, Lundgren suggested a successful forcing, applied in physical space. The latter approach unfortunately lacks predicting the integral length scale of turbulence. The present study provides a forcing method based on a reconstruction approach which consists in building fluctuations with a turbulent synthetic velocity field based on a prescribed energy spectrum model. The proposed approach is assessed by performing large-eddy simulations of a sustained homogeneous isotropic turbulence in a triply periodic box of size L = 2pi. Properties of the new forcing technique are discussed, drawing on both spatial and time correlations and also on the shape of energy spectrum together with the level of resolved turbulent kinetic energy. A special attention is put on the control of resolved turbulent energy. In this framework, an efficient selective forcing technique is derived, making use of spectral space features. The results show that the proposed approach allows to drive efficiently the resolved kinetic energy towards its target value while preserving the integral length scale independent of the domain size. It is observed that the resulting longitudinal length scale is overestimated by 13%, while the two-time correlations are recovered when using stochastic frequencies.
Jérémie Janin, Fabien Duval, Christophe Friess, Pierre Sagaut. A new linear forcing method for isotropic turbulence with controlled integral length scale. Physics of Fluids, 2021, 33 (4), pp.045127. ⟨10.1063/5.0045818⟩. ⟨hal-03326165⟩
Florian Renard, Yongliang Feng, Jean-François Boussuge, Pierre Sagaut. Improved compressible hybrid lattice Boltzmann method on standard lattice for subsonic and supersonic flows. Computers and Fluids, 2021, 219, pp.104867. ⟨10.1016/j.compfluid.2021.104867⟩. ⟨hal-03326159⟩ Plus de détails...
A D2Q9 Hybrid Lattice Boltzmann Method (HLBM) is proposed for the simulation of both compressible subsonic and supersonic flows. This HLBM is an extension of the model of Feng et al. [1], which has been found, via different test cases, to be unstable for supersonic regimes. To circumvent this limitation, we propose:: (1) a new discretization of the lattice closure correction term that makes possible the simulation of supersonic flows, (2) a corrected viscous stress tensor that takes into account polyatomic gases, and (3) a novel discretization of the viscous heat production term fitting with the regularized formalism. The result is a hybrid method that resolves the mass and momentum equations with an LBM algorithm, and resolves the entropy-based energy equation with a finite volume method. This approach fully recovers the physics of the Navier-Stokes-Fourier equations with the ideal gas equation of state, and is valid from subsonic to supersonic regimes. It is then successfully assessed with both smooth flows and flows involving shocks. The proposed model is shown to be an efficient, accurate, and robust alternative to classic Navier-Stokes methods for the simulation of compressible flows.
Florian Renard, Yongliang Feng, Jean-François Boussuge, Pierre Sagaut. Improved compressible hybrid lattice Boltzmann method on standard lattice for subsonic and supersonic flows. Computers and Fluids, 2021, 219, pp.104867. ⟨10.1016/j.compfluid.2021.104867⟩. ⟨hal-03326159⟩
S. Guo, Y. Feng, Pierre Sagaut. On the use of conservative formulation of energy equation in hybrid compressible lattice Boltzmann method. Computers and Fluids, 2021, 219, pp.104866. ⟨10.1016/j.compfluid.2021.104866⟩. ⟨hal-03597478⟩ Plus de détails...
Effect of density variations on mass conservation properties is widely recognized in the lattice Boltzmann method (LBM), thus non-conservative form of scalar transport equation was commonly adopted within the framework of hybrid LBM. Focusing on the compressible hybrid LBM, mass conservation and its effect on energy conservation equation are studied in this paper. Starting from the analysis on mass conservation law recovered by LBM, the consistency between conservative and non-conservative formulations of energy conservation equation based on various thermodynamic variables and lattice Boltzmann equation is addressed. Driven by the theoretical analysis, a set of modified consistent energy equations in entropy and internal energy form is derived to reduce the error terms and improve the consistency. The theoretical analysis and modified energy equations are intensively evaluated by several numerical test cases, e.g., the isentropic vortex convection, three-dimensional compressible Taylor-Green vortex and shock-vortex interaction.
S. Guo, Y. Feng, Pierre Sagaut. On the use of conservative formulation of energy equation in hybrid compressible lattice Boltzmann method. Computers and Fluids, 2021, 219, pp.104866. ⟨10.1016/j.compfluid.2021.104866⟩. ⟨hal-03597478⟩
E. Laribi, E. Serre, P. Tamain, H. Yang. Impact of negative triangularity on edge plasma transport and turbulence in TOKAM3X simulations. Nuclear Materials and Energy, 2021, pp.101012. ⟨10.1016/j.nme.2021.101012⟩. ⟨hal-03214958⟩ Plus de détails...
The impact of triangularity on edge plasma transport and turbulence is addressed from full 3D turbulence simulations performed with TOKAM3X. Flux driven fluid simulations are run on analytical magnetic equilibria generated with positive and negative triangularity δ in a bottom limiter configuration. The conservation of the energy is assured by the increase of the bottom limiter radial position from δ > 0 to δ < 0. Changing the triangularity impacts both the plasma equilibrium and the turbulence. In particular, negative triangularity leads to a reduction of the density and electron temperature decay lengths in agreement with the literature. Concerning the turbulence, in all the simulations, it remains ballooned with an enhanced level of fluctuations at low field side in comparison to the high field one. Moreover, no clear trend is visible on the relative level of fluctuations of both density and electron temperature in the CFR whereas an enhancement (resp. reduction) is visible in the scrape-off layer at the low field side midplane for the negative (resp. positive) triangularity simulations. This behaviour differs from TCV and DIII-D measurements which show the benefit of negative triangularity in terms of turbulence reduction and increased confinement. However, no conclusion is drawn from our preliminary study concerning the impact of triangularity on the turbulent transport. Change in triangularity impacts many simulation control parameters, as in the experiments, and that the analysis of its impact alone on the dynamics of the plasma is not obvious in this configuration.
E. Laribi, E. Serre, P. Tamain, H. Yang. Impact of negative triangularity on edge plasma transport and turbulence in TOKAM3X simulations. Nuclear Materials and Energy, 2021, pp.101012. ⟨10.1016/j.nme.2021.101012⟩. ⟨hal-03214958⟩
S. Guo, Y. Feng, Pierre Sagaut. On the use of conservative formulation of energy equation in hybrid compressible lattice Boltzmann method. Computers and Fluids, 2021, 219, pp.104866. ⟨10.1016/j.compfluid.2021.104866⟩. ⟨hal-03326128⟩ Plus de détails...
Effect of density variations on mass conservation properties is widely recognized in the lattice Boltzmann method (LBM), thus non-conservative form of scalar transport equation was commonly adopted within the framework of hybrid LBM. Focusing on the compressible hybrid LBM, mass conservation and its effect on energy conservation equation are studied in this paper. Starting from the analysis on mass conservation law recovered by LBM, the consistency between conservative and non-conservative formulations of energy conservation equation based on various thermodynamic variables and lattice Boltzmann equation is addressed. Driven by the theoretical analysis, a set of modified consistent energy equations in entropy and internal energy form is derived to reduce the error terms and improve the consistency. The theoretical analysis and modified energy equations are intensively evaluated by several numerical test cases, e.g., the isentropic vortex convection, three-dimensional compressible Taylor-Green vortex and shock-vortex interaction.
S. Guo, Y. Feng, Pierre Sagaut. On the use of conservative formulation of energy equation in hybrid compressible lattice Boltzmann method. Computers and Fluids, 2021, 219, pp.104866. ⟨10.1016/j.compfluid.2021.104866⟩. ⟨hal-03326128⟩
Shang-Gui Cai, Johan Degrigny, Jean-François Boussuge, Pierre Sagaut. Coupling of turbulence wall models and immersed boundaries on Cartesian grids. Journal of Computational Physics, 2021, 429, pp.109995. ⟨10.1016/j.jcp.2020.109995⟩. ⟨hal-03597064⟩ Plus de détails...
An improved coupling of immersed boundary method and turbulence wall models on Cartesian grids is proposed, for producing smooth wall surface pressure and skin friction at high Reynolds numbers. Spurious oscillations are frequently observed on these quantities with most immersed boundary wall modeling methods, especially for the skin friction which is found to be very sensitive to the solid surface's position and orientation against the Cartesian grids. The problem originates from the irregularity of the wall distance on the stair-step grid boundaries where the immersed boundary conditions are applied. To reduce this directional error, several modifications are presented to enhance the near wall solution. First, the commonly used interpolation for the flow velocity is replaced by one for the friction velocity, which has much less variation near wall. The concept of using a fictitious point to retrieve flow fields in the wall normal direction is abandoned and the interpolation is performed in the wall parallel plane with existing fluid points. Secondly, the velocity gradients at the approximated boundary are computed with advanced schemes and the normal gradient of the tangential velocity is reconstructed from the wall laws. To further protect the near wall solution, the normal velocity gradient and the working viscosity from the Spalart-Allmaras turbulence model are enforced by their theoretical solutions in the interior fluid close to the wall. Additionally, various post-processing algorithms for reconstructing wall surface quantities and force integrations are investigated. Other related factors are also discussed for their effects on the results. The validity of present method has been demonstrated through numerical benchmark tests on a flat plate at zero pressure gradient, both aligned and inclined with respect to the grid, as well as aerodynamic cases of NACA 23012 airfoil and NASA trap wing.
Shang-Gui Cai, Johan Degrigny, Jean-François Boussuge, Pierre Sagaut. Coupling of turbulence wall models and immersed boundaries on Cartesian grids. Journal of Computational Physics, 2021, 429, pp.109995. ⟨10.1016/j.jcp.2020.109995⟩. ⟨hal-03597064⟩
The boundary slip error resulting from the interpolation/spreading non-reciprocity of the direct-forcing immersedboundary method is analyzed based on a simple and generic theoretical framework. In explicit implementations, the slip error scales with the Courant number, as predicted by the analysis and confirmed by lattice-Boltzmann simulation results. Using an analytical approximation of the non-reciprocity error, the immersed-boundary force can be corrected in order to prevent boundary slip and flow penetration. This a priori correction leads to a major improvement of the no-slip condition while avoiding any additional computational time or implementation effort.
Simon Gsell, Julien Favier. Direct-forcing immersed-boundary method: a simple correction preventing boundary slip error. Journal of Computational Physics, 2021, 435, pp.110265. ⟨10.1016/j.jcp.2021.110265⟩. ⟨hal-03425864⟩
Jincheng Lou, Jacob Johnston, Tzahi Y. Cath, Denis Martinand, Nils Tilton. Computational fluid dynamics simulations of unsteady mixing in spacer-filled direct contact membrane distillation channels. Journal of Membrane Science, 2021, 622, pp.118931. ⟨10.1016/j.memsci.2020.118931⟩. ⟨hal-03597607⟩ Plus de détails...
Direct contact membrane distillation (DCMD) is a promising means of concentrating brines to their saturation limit. During that process, membrane spacers play a key role in temperature polarization, concentration polarization, and mineral scaling. These interactions are not well understood, because they are difficult to study experimentally and numerically, and the flow regimes are not fully charted. We consequently develop a tailored in-house CFD code that simulates unsteady two-dimensional heat and mass transport in plate-and-frame DCMD systems with cylindrical spacers. The code uses a combination of finite-volume methods in space, projection methods in time, and recent advances in immersed boundary methods for the spacer surfaces. Using the code, we explore how the transition to unsteady laminar vortex shedding affects polarization and permeate production of DCMD systems. We show that the impact of spacers can be explained by examining the various steady and unsteady vortical flow structures generated in the bulk and near the membranes. Overall, we show that though unsteady vortex structures tend to mix temperature polarization layers with the bulk, they are not similarly able to mix the concentration layers. Rather, vortical structures tend to create regions of preferential salt accumulation. In the vortex shedding regime, the net result is that spacers often increase vapor production at the expense of increasing the risk of mineral scaling.
Jincheng Lou, Jacob Johnston, Tzahi Y. Cath, Denis Martinand, Nils Tilton. Computational fluid dynamics simulations of unsteady mixing in spacer-filled direct contact membrane distillation channels. Journal of Membrane Science, 2021, 622, pp.118931. ⟨10.1016/j.memsci.2020.118931⟩. ⟨hal-03597607⟩
Isabelle Cheylan, Song Zhao, Pierre Boivin, Pierre Sagaut. Compressible pressure-based Lattice-Boltzmann applied to humid air with phase change. Applied Thermal Engineering, 2021, pp.116868. ⟨10.1016/j.applthermaleng.2021.116868⟩. ⟨hal-03180596⟩ Plus de détails...
A new compressible pressure-based Lattice Boltzmann Method is proposed to simulate humid air flows with phase change. The variable density and compressible effects are fully resolved, effectively lifting the Boussinesq approximation commonly used, e.g. for meteorological flows. Previous studies indicate that the Boussinesq assumption can lead to errors up to 25%, but the model remains common, for compressible models often suffer from a lack of stability. In order to overcome this issue, a new pressure-based solver is proposed, exhibiting excellent stability properties. Mass and momentum conservation equations are solved by a hybrid recursive regularized Lattice-Boltzmann approach, whereas the enthalpy and species conservation equations are solved using a finite volume method. The solver is based on a pressure-based method coupled with a predictor-corrector algorithm, and incorporates a humid equation of state, as well as a specific boundary condition treatment for phase change. In particular, boundary conditions that handle mass leakage are also proposed and validated. Three test cases are investigated in order to validate this new approach: the Rayleigh-Bénard instability applied to humid air, the atmospheric rising of a condensing moist bubble, and finally the evaporation of a thin liquid film in a vertical channel. Results indicate that the proposed pressure-based Lattice-Boltzmann model is stable and accurate on all cases.
Isabelle Cheylan, Song Zhao, Pierre Boivin, Pierre Sagaut. Compressible pressure-based Lattice-Boltzmann applied to humid air with phase change. Applied Thermal Engineering, 2021, pp.116868. ⟨10.1016/j.applthermaleng.2021.116868⟩. ⟨hal-03180596⟩
Yongliang Feng, Johann Miranda‐fuentes, Shaolong Guo, Jérôme Jacob, Pierre Sagaut. ProLB: A Lattice Boltzmann Solver of Large‐Eddy Simulation for Atmospheric Boundary Layer Flows. Journal of Advances in Modeling Earth Systems, 2021, 13 (3), pp.e2020MS002107. ⟨10.1029/2020MS002107⟩. ⟨hal-03326123⟩ Plus de détails...
A large-eddy simulation tool is developed for simulating the dynamics of atmospheric boundary layers (ABLs) using lattice Boltzmann method (LBM), which is an alternative approach for computational fluid dynamics and proved to be very well suited for the simulation of low-Mach flows. The equations of motion are coupled with the global complex physical models considering the coupling among several mechanisms, namely basic hydro-thermodynamics and body forces related to stratification, Coriolis force, canopy effects, humidity transport, and condensation. Mass and momentum equations are recovered by an efficient streaming, collision, and forcing process within the framework of LBM while the governing equations of temperature, liquid, and vapor water fraction are solved using a finite volume method. The implementation of wall models for ABL, subgrid models, and interaction terms related to multiphysic phenomena (e.g., stratification, condensation) is described, implemented, and assessed in this study. An immersed boundary approach is used to handle flows in complex configurations, with application to flows in realistic urban areas. Applications to both wind engineering and atmospheric pollutant dispersion are illustrated.
Yongliang Feng, Johann Miranda‐fuentes, Shaolong Guo, Jérôme Jacob, Pierre Sagaut. ProLB: A Lattice Boltzmann Solver of Large‐Eddy Simulation for Atmospheric Boundary Layer Flows. Journal of Advances in Modeling Earth Systems, 2021, 13 (3), pp.e2020MS002107. ⟨10.1029/2020MS002107⟩. ⟨hal-03326123⟩
Journal: Journal of Advances in Modeling Earth Systems
Jincheng Lou, Jacob Johnston, Tzahi Cath, Denis Martinand, Nils Tilton. Computational fluid dynamics simulations of unsteady mixing in spacer-filled direct contact membrane distillation channels. Journal of Membrane Science, 2021, 622, pp.118931. ⟨10.1016/j.memsci.2020.118931⟩. ⟨hal-03515318⟩ Plus de détails...
Direct contact membrane distillation (DCMD) is a promising means of concentrating brines to their saturation limit. During that process, membrane spacers play a key role in temperature polarization, concentration polarization, and mineral scaling. These interactions are not well understood, because they are difficult to study experimentally and numerically, and the flow regimes are not fully charted. We consequently develop a tailored in-house CFD code that simulates unsteady two-dimensional heat and mass transport in plate-and-frame DCMD systems with cylindrical spacers. The code uses a combination of finite-volume methods in space, projection methods in time, and recent advances in immersed boundary methods for the spacer surfaces. Using the code, we explore how the transition to unsteady laminar vortex shedding affects polarization and permeate production of DCMD systems. We show that the impact of spacers can be explained by examining the various steady and unsteady vortical flow structures generated in the bulk and near the membranes. Overall, we show that though unsteady vortex structures tend to mix temperature polarization layers with the bulk, they are not similarly able to mix the concentration layers. Rather, vortical structures tend to create regions of preferential salt accumulation. In the vortex shedding regime, the net result is that spacers often increase vapor production at the expense of increasing the risk of mineral scaling.
Jincheng Lou, Jacob Johnston, Tzahi Cath, Denis Martinand, Nils Tilton. Computational fluid dynamics simulations of unsteady mixing in spacer-filled direct contact membrane distillation channels. Journal of Membrane Science, 2021, 622, pp.118931. ⟨10.1016/j.memsci.2020.118931⟩. ⟨hal-03515318⟩
Y. Feng, J. Miranda-Fuentes, Jérôme Jacob, Pierre Sagaut. Hybrid lattice Boltzmann model for atmospheric flows under anelastic approximation. Physics of Fluids, 2021, 33 (3), pp.036607. ⟨10.1063/5.0039516⟩. ⟨hal-03326143⟩ Plus de détails...
Lattice Boltzmann (LB) method for atmospheric dynamics is developed by considering the characteristics of the anelastic approximation. After introducing reference base state values in atmospheric flows, an LB model, with an external force term, has been constructed in anelastic framework. In the proposed anelastic LB model, mass and momentum conservation equations are solved by the LB method with a regularization procedure, and temperature field or scalar transport is simulated by finite volume method. The derived macroscopic governing equations from the anelastic model are analyzed and discussed in Chapman-Enskog asymptotic expansion. The anelastic LB model is assessed considering three benchmarks including a non-hydrostatic atmospheric inviscid convection, two-dimensional density currents, and inertia-gravity waves in stably stratified atmospheric layer. The validations demonstrate that the anelastic extension of the LB method can simulate atmospheric flows effectively and accurately. Besides, the proposed model offers a unified framework for both Boussinesq approximation and anelastic approximation, which is largely free of characteristic depth of atmospheric flows.
Y. Feng, J. Miranda-Fuentes, Jérôme Jacob, Pierre Sagaut. Hybrid lattice Boltzmann model for atmospheric flows under anelastic approximation. Physics of Fluids, 2021, 33 (3), pp.036607. ⟨10.1063/5.0039516⟩. ⟨hal-03326143⟩
Y. Feng, J. Miranda-Fuentes, Jérôme Jacob, Pierre Sagaut. Hybrid lattice Boltzmann model for atmospheric flows under anelastic approximation. Physics of Fluids, 2021, 33 (3), pp.036607. ⟨10.1063/5.0039516⟩. ⟨hal-03597258⟩ Plus de détails...
Lattice Boltzmann (LB) method for atmospheric dynamics is developed by considering the characteristics of the anelastic approximation. After introducing reference base state values in atmospheric flows, an LB model, with an external force term, has been constructed in anelastic framework. In the proposed anelastic LB model, mass and momentum conservation equations are solved by the LB method with a regularization procedure, and temperature field or scalar transport is simulated by finite volume method. The derived macroscopic governing equations from the anelastic model are analyzed and discussed in Chapman-Enskog asymptotic expansion. The anelastic LB model is assessed considering three benchmarks including a non-hydrostatic atmospheric inviscid convection, two-dimensional density currents, and inertia-gravity waves in stably stratified atmospheric layer. The validations demonstrate that the anelastic extension of the LB method can simulate atmospheric flows effectively and accurately. Besides, the proposed model offers a unified framework for both Boussinesq approximation and anelastic approximation, which is largely free of characteristic depth of atmospheric flows.
Y. Feng, J. Miranda-Fuentes, Jérôme Jacob, Pierre Sagaut. Hybrid lattice Boltzmann model for atmospheric flows under anelastic approximation. Physics of Fluids, 2021, 33 (3), pp.036607. ⟨10.1063/5.0039516⟩. ⟨hal-03597258⟩
Simon Gsell, Umberto d'Ortona, Julien Favier. Lattice-Boltzmann simulation of creeping generalized Newtonian flows: theory and guidelines. Journal of Computational Physics, 2021, 429, pp.109943. ⟨10.1016/j.jcp.2020.109943⟩. ⟨hal-03166492⟩ Plus de détails...
The accuracy of the lattice-Boltzmann (LB) method is related to the relaxation time controlling the flow viscosity. In particular, it is often recommended to avoid large fluid viscosities in order to satisfy the low-Knudsen-number assumption that is essential to recover hydrodynamic behavior at the macroscopic scale, which may in principle limit the possibility of simulating creeping flows and non-Newtonian flows involving important viscosity variations. Here it is shown, based on the continuous Boltzmann equations, that a two-relaxation-time (TRT) model can however recover the steady Navier-Stokes equations without any restriction on the fluid viscosity, provided that the Knudsen number is redefined as a function of both relaxation times. This effective Knudsen number is closely related to the previously-described parameter controlling numerical errors of the TRT model, providing a consistent theory at both the discrete and continuous levels. To simulate incompressible flows, the viscous incompressibility condition M a 2 /Re 1 also needs to be satisfied, where M a and Re are the Mach and Reynolds numbers. This concept is extended by defining a local incompressibility factor, allowing one to locally control the accuracy of the simulation for flows involving varying viscosities. These theoretical arguments are illustrated based on numerical simulations of the two-dimensional flow past a square cylinder. In the case of a Newtonian flow, the viscosity independence is confirmed for relaxation times up to 10 4 , and the ratio M a 2 /Re = 0.1 is small enough to ensure reliable incompressible simulations. The Herschel-Bulkley model is employed to introduce shear-dependent viscosities in the flow. The proposed numerical strategy allows to achieve major viscosity variations, avoiding the implementation of artificial viscosity cutoff in high-viscosity regions. Highly non-linear flows are simulated over ranges of the Bingham number Bn ∈ [1, 1000] and flow index n ∈ [0.2, 1.8], and successfully compared to prior numerical works based on Navier-Stokes solvers. This work provides a general framework to simulate complex creeping flows, as encountered in many biological and industrial systems, using the lattice-Boltzmann method.
Simon Gsell, Umberto d'Ortona, Julien Favier. Lattice-Boltzmann simulation of creeping generalized Newtonian flows: theory and guidelines. Journal of Computational Physics, 2021, 429, pp.109943. ⟨10.1016/j.jcp.2020.109943⟩. ⟨hal-03166492⟩
Jérôme Jacob, Lucie Merlier, Felix Marlow, Pierre Sagaut. Lattice Boltzmann Method-Based Simulations of Pollutant Dispersion and Urban Physics. Atmosphere, 2021, 12 (7), pp.833. ⟨10.3390/atmos12070833⟩. ⟨hal-03326148⟩ Plus de détails...
Mesocale atmospheric flows that develop in the boundary layer or microscale flows that develop in urban areas are challenging to predict, especially due to multiscale interactions, multiphysical couplings, land and urban surface thermal and geometrical properties and turbulence. However, these different flows can indirectly and directly affect the exposure of people to deteriorated air quality or thermal environment, as well as the structural and energy loads of buildings. Therefore, the ability to accurately predict the different interacting physical processes determining these flows is of primary importance. To this end, alternative approaches based on the lattice Boltzmann method (LBM) wall model large eddy simulations (WMLESs) appear particularly interesting as they provide a suitable framework to develop efficient numerical methods for the prediction of complex large or smaller scale atmospheric flows. In particular, this article summarizes recent developments and studies performed using the hybrid recursive regularized collision model for the simulation of complex or/and coupled turbulent flows. Different applications to the prediction of meteorological humid flows, urban pollutant dispersion, pedestrian wind comfort and pressure distribution on urban buildings including uncertainty quantification are especially reviewed. For these different applications, the accuracy of the developed approach was assessed by comparison with experimental and/or numerical reference data, showing a state of the art performance. Ongoing developments focus now on the validation and prediction of indoor environmental conditions including thermal mixing and pollutant dispersion in different types of rooms equipped with heat, ventilation and air conditioning systems.
Jérôme Jacob, Lucie Merlier, Felix Marlow, Pierre Sagaut. Lattice Boltzmann Method-Based Simulations of Pollutant Dispersion and Urban Physics. Atmosphere, 2021, 12 (7), pp.833. ⟨10.3390/atmos12070833⟩. ⟨hal-03326148⟩
G. Farag, T. Coratger, G. Wissocq, S. Zhao, Pierre Boivin, et al.. A unified hybrid lattice-Boltzmann method for compressible flows: Bridging between pressure-based and density-based methods. Physics of Fluids, 2021, 33 (8), pp.086101. ⟨10.1063/5.0057407⟩. ⟨hal-03324229⟩ Plus de détails...
A unified expression for high-speed compressible segregated consistent lattice Boltzmann methods, namely, pressure-based and improved density-based methods, is given. It is theoretically proved that in the absence of forcing terms, these approaches are strictly identical and can be recast in a unique form. An important result is that the difference with classical density-based methods lies in the addition of fourth-order term in the equilibrium function. It is also shown that forcing terms used to balance numerical errors in both original pressure-based and improved density-based methods can be written in a generalized way. A hybrid segregated efficient lattice-Boltzmann for compressible flow based on this unified model, equipped with a recursive regularization kernel, is proposed and successfully assessed on a wide set of test cases with and without shock waves.
G. Farag, T. Coratger, G. Wissocq, S. Zhao, Pierre Boivin, et al.. A unified hybrid lattice-Boltzmann method for compressible flows: Bridging between pressure-based and density-based methods. Physics of Fluids, 2021, 33 (8), pp.086101. ⟨10.1063/5.0057407⟩. ⟨hal-03324229⟩
Johan Degrigny, Shang-Gui Cai, Jean-François Boussuge, Pierre Sagaut. Improved wall model treatment for aerodynamic flows in LBM. Computers and Fluids, 2021, 227, pp.105041. ⟨10.1016/j.compfluid.2021.105041⟩. ⟨hal-03597146⟩ Plus de détails...
The article deals with an improved treatment of wall models for the simulation of turbulent flows in the framework of Immersed Wall Boundaries on Cartesian grids. The emphasis is put on the implementa-tion in a Lattice-Boltzmann Method solver without loss of generality, since the proposed approach can be used in Navier-Stokes-based solvers in a straightforward way. The proposed improved wall model im-plementation relies on the combination of several key elements, namely i) the removal of grid points too close to the solid surface and ii) an original computation of wall normal velocity gradient and iii) the interpolation scheme. The new method is successfully assessed considering URANS simulations focusing on steady solutions of the Zero Pressure Gradient turbulent flat plate boundary layer and the turbulent flow around a NACA0012 airfoil at several angles of attack.
Johan Degrigny, Shang-Gui Cai, Jean-François Boussuge, Pierre Sagaut. Improved wall model treatment for aerodynamic flows in LBM. Computers and Fluids, 2021, 227, pp.105041. ⟨10.1016/j.compfluid.2021.105041⟩. ⟨hal-03597146⟩
Raffaele Tatali, Eric Serre, Patrick Tamain, Davide Galassi, Philippe Ghendrih, et al.. Impact of collisionality on turbulence in the edge of tokamak plasma using 3D global simulations. Nuclear Fusion, 2021, ⟨10.1088/1741-4326/abe98b⟩. ⟨hal-03182318⟩ Plus de détails...
Collisionality is one of the key parameters in determining turbulent transport in the plasma edge, regulating phenomena such as "shoulder formation", separation of scale lengths in the scrape-off layer, turbulence damping and zonal flow dynamics. Understanding its role is therefore of primary importance for future reactors like ITER. Obtaining reliable predictions and a better characterization of plasma flow properties when varying collisionality remains, however, a critical challenge for the simulations. This paper focuses on the impact of varying collisionality in a nonisothermal three-dimensional fluid model of the plasma edge. A high field side limited configuration encompassing open and closed magnetic field lines with parameters typical of a medium-sized tokamak is considered. The present model can consistently account for the variations of collisionality and its impact on both the parallel resistivity η and the ion and electron parallel thermal conductivities χ e,i. Details on mean flow and turbulence properties are given. Changing collisionality leads to significant changes in the flow properties both on the mean and fluctuating quantities. In particular, lowering collisionality decreases the size of coherent structures, the fluctuation levels of turbulence, and steepens the density and temperature equilibrium profiles around the separatrix leading to a global reduction of the turbulent transport. The scrape-off layer (SOL) width is observed to increase with collisionality, eventually resulting in the disappearance of the scale lengths separation between near and far SOL, consistently with previous experimental observations. At low collisionality, where the presence of narrow feature is well-established, a contribution of heat conduction increases up to compete with heat convection.
Raffaele Tatali, Eric Serre, Patrick Tamain, Davide Galassi, Philippe Ghendrih, et al.. Impact of collisionality on turbulence in the edge of tokamak plasma using 3D global simulations. Nuclear Fusion, 2021, ⟨10.1088/1741-4326/abe98b⟩. ⟨hal-03182318⟩
B Luce, P Tamain, G Ciraolo, Ph Ghendrih, G Giorgiani, et al.. Impact of three-dimensional magnetic perturbations on turbulence in tokamak edge plasmas. Plasma Physics and Controlled Fusion, 2021, ⟨10.1088/1361-6587/abf03f⟩. ⟨hal-03144400⟩ Plus de détails...
The impact of resonant magnetic perturbations (RMP) on the plasma edge equilibrium and on the turbulence is investigated in a circular limited configuration. The study is based on a Braginski-based isothermal fluid model. The flow response of an unperturbed case to a small amplitude three-dimensional single mode RMP is studied and a scan in amplitude and poloidal and toroidal mode number is performed. Special attention is given when magnetic islands appear in the simulation domain on flux surfaces of rational safety factor. Results show an impact of Magnetic Perturbations (MPs) on both the plasma equilibrium and on the turbulence properties, with a deviation to the reference solution which depends on the MPs amplitude and on their wavenumbers. The impact of MPs on turbulence is however globally weaker than on the plasma equilibrium, suggesting a stabilizing effect of the MP on turbulent transport. Experimental trends are recovered such as the density pump-out and the increase of the radial electric field as well as the reorganization of the parallel velocity. The ballooning of the transport is modified under the effect of the perturbations, with a shift of the peaked poloidal region from the upper to the lower outer midplane. In the present model, the SOL width is observed decreasing in the presence of MPs. Turbulence properties are also impacted with the density fluctuations level decreasing in perturbed solutions and the intermittency is globally weakened.
B Luce, P Tamain, G Ciraolo, Ph Ghendrih, G Giorgiani, et al.. Impact of three-dimensional magnetic perturbations on turbulence in tokamak edge plasmas. Plasma Physics and Controlled Fusion, 2021, ⟨10.1088/1361-6587/abf03f⟩. ⟨hal-03144400⟩
B D Dudson, W A Gracias, R Jorge, A H Nielsen, J M B Olsen, et al.. Edge turbulence in ISTTOK: a multi-code fluid validation. Plasma Physics and Controlled Fusion, 2021. ⟨hal-03179634⟩ Plus de détails...
B D Dudson, W A Gracias, R Jorge, A H Nielsen, J M B Olsen, et al.. Edge turbulence in ISTTOK: a multi-code fluid validation. Plasma Physics and Controlled Fusion, 2021. ⟨hal-03179634⟩
G. Ciraolo, S. Di Genova, H. Yang, A. Gallo, N. Fedorczak, et al.. INTERPRETATIVE MODELING OF IMPURITY TRANSPORT AND TUNGSTEN SOURCES IN WEST BOUNDARY PLASMA. Nuclear Fusion, 2021, 61 (12), pp.126015. ⟨10.1088/1741-4326/ac2439⟩. ⟨hal-03420146⟩ Plus de détails...
The contamination of core plasma by high-Z impurities, especially tungsten (W), is the main reason of very high level of radiated power in WEST experiments. Intrinsic light impurities, mainly oxygen and carbon, play a dominant role in the sputtering of W on plasma facing components. In this contribution, we present a detailed analysis of WEST experiments supported by numerical modeling performed with the transport code SOLEDGE-EIRENE providing a clear picture of light impurities transport and poloidal distribution. Moreover, making use of SOLEDGE-ERO2.0 simulations, possible strategies to reduce core contamination due to W penetration are presented. .
G. Ciraolo, S. Di Genova, H. Yang, A. Gallo, N. Fedorczak, et al.. INTERPRETATIVE MODELING OF IMPURITY TRANSPORT AND TUNGSTEN SOURCES IN WEST BOUNDARY PLASMA. Nuclear Fusion, 2021, 61 (12), pp.126015. ⟨10.1088/1741-4326/ac2439⟩. ⟨hal-03420146⟩
Shaolong Guo, Wen-Quan Tao. A robustness-enhanced method for Riemann solver. International Journal of Heat and Mass Transfer, 2020, 166, pp.120757. ⟨10.1016/j.ijheatmasstransfer.2020.120757⟩. ⟨hal-03597492⟩ Plus de détails...
The appearance of shock anomaly is a major unsolved problem for some low diffusion schemes when simulating the hypersonic flow. In this paper, a simple method is proposed to enhance the robustness of the low diffusion schemes to overcome the shock anomaly. The main idea of this method is adding an appropriate extra term to the original low diffusion schemes without influencing the accuracy in aerodynamic heating prediction. This extra term is derived from the difference between the flux splitting scheme (FVS) and the advection upstream splitting method+ (AUSM+). Adding this term to three low diffusion schemes, seven typical numerical tests are conducted to examine the capability of those schemes. Numerical results show that the three new schemes turn out to be carbuncle-free and shock-stable without losing their original accuracy in prediction of aerodynamic heating, validating the feasibility and reliability of the proposed method.
Shaolong Guo, Wen-Quan Tao. A robustness-enhanced method for Riemann solver. International Journal of Heat and Mass Transfer, 2020, 166, pp.120757. ⟨10.1016/j.ijheatmasstransfer.2020.120757⟩. ⟨hal-03597492⟩
Journal: International Journal of Heat and Mass Transfer
Christophe Friess, Lars Davidson. A formulation of PANS capable of mimicking IDDES. International Journal of Heat and Fluid Flow, 2020, 86, pp.108666. ⟨10.1016/j.ijheatfluidflow.2020.108666⟩. ⟨hal-02944327⟩ Plus de détails...
Christophe Friess, Lars Davidson. A formulation of PANS capable of mimicking IDDES. International Journal of Heat and Fluid Flow, 2020, 86, pp.108666. ⟨10.1016/j.ijheatfluidflow.2020.108666⟩. ⟨hal-02944327⟩
Journal: International Journal of Heat and Fluid Flow
S. Zhao, G. Farag, Pierre Boivin, P. Sagaut. Toward fully conservative hybrid lattice Boltzmann methods for compressible flows. Physics of Fluids, 2020, 32 (12), pp.126118. ⟨10.1063/5.0033245⟩. ⟨hal-03087980⟩ Plus de détails...
S. Zhao, G. Farag, Pierre Boivin, P. Sagaut. Toward fully conservative hybrid lattice Boltzmann methods for compressible flows. Physics of Fluids, 2020, 32 (12), pp.126118. ⟨10.1063/5.0033245⟩. ⟨hal-03087980⟩
Tatyana Lyubimova, Anatoly Lepikhin, Yanina Parshakova, Vadim Kolchanov, Carlo Gualtieri, et al.. A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions. Water, 2020, 12 (11), pp.2969. ⟨10.3390/w12112969⟩. ⟨hal-02989736⟩ Plus de détails...
A rapid downstream weakening of the processes that drive the intensity of transverse mixing at the confluence of large rivers has been identified in the literature and attributed to the progressive reduction in channel scale secondary circulation and shear-driven mixing with distance downstream from the junction. These processes are investigated in this paper using a three-dimensional computation of the Reynolds averaged Navier Stokes equations combined with a Reynolds stress turbulence model for the confluence of the Kama and Vishera rivers in the Russian Urals. Simulations were carried out for three different configurations: an idealized planform with a rectangular cross-section (R), the natural planform with a rectangular cross-section (P), and the natural planform with the measured bathymetry (N), each one for three different discharge ratios. Results show that in the idealized configuration (R), the initial vortices that form due to channel-scale pressure gradients decline rapidly with distance downstream. Mixing is slow and incomplete at more than 10 multiples of channel width downstream from the junction corner. However, when the natural planform and bathymetry are introduced (N), rates of mixing increase dramatically at the junction corner and are maintained with distance downstream. Comparison with the P case suggests that it is the bathymetry that drives the most rapid mixing and notably when the discharge ratio is such that a single channel-scale vortex develops aided by curvature in the post junction channel. This effect is strongest when the discharge of the tributary that has the same direction of curvature as the post junction channel is greatest. A comprehensive set of field data are required to test this conclusion. If it holds, theoretical models of mixing processes in rivers will need to take into account the effects of bathymetry upon the interaction between river discharge ratio, secondary circulation development, and mixing rates.
Tatyana Lyubimova, Anatoly Lepikhin, Yanina Parshakova, Vadim Kolchanov, Carlo Gualtieri, et al.. A Numerical Study of the Influence of Channel-Scale Secondary Circulation on Mixing Processes Downstream of River Junctions. Water, 2020, 12 (11), pp.2969. ⟨10.3390/w12112969⟩. ⟨hal-02989736⟩
Thomas Astoul, Gauthier Wissocq, Jean-François Boussuge, Alois Sengissen, Pierre Sagaut. Analysis and reduction of spurious noise generated at grid refinement interfaces with the lattice Boltzmann method. Journal of Computational Physics, 2020, 418, pp.109645. ⟨10.1016/j.jcp.2020.109645⟩. ⟨hal-02960150⟩ Plus de détails...
The present study focuses on the unphysical effects induced by the use of non-uniform grids in the lattice Boltzmann method. In particular, the convection of vortical structures across a grid refinement interface is likely to generate spurious noise that may impact the whole computation domain. This issue becomes critical in the case of aeroacoustic simulations, where accurate pressure estimations are of paramount importance. The purpose of this article is to identify the issues occurring at the interface and to propose possible solutions yielding significant improvements for aeroacoustic simulations. More specifically, this study highlights the critical involvement of non-physical modes in the generation of spurious vorticity and acoustics. The identification of these modes is made possible thanks to linear stability analyses performed in the fluid core, and non-hydrodynamic sensors specifically developed to systematically emphasize them during a simulation. Investigations seeking pure acoustic waves and sheared flows allow for isolating the contribution of each mode. An important result is that spurious wave generation is intrinsically due to the change in the grid resolution (i.e. aliasing) independently of the details of the grid transition algorithm. Finally, the solution proposed to minimize spurious wave amplitude consists of choosing an appropriate collision model in the fluid core so as to cancel the non-hydrodynamic mode contribution regardless the grid coupling algorithm. Results are validated on a convected vortex and on a turbulent flow around a cylinder where a huge reduction of both spurious noise and vorticity are obtained.
Thomas Astoul, Gauthier Wissocq, Jean-François Boussuge, Alois Sengissen, Pierre Sagaut. Analysis and reduction of spurious noise generated at grid refinement interfaces with the lattice Boltzmann method. Journal of Computational Physics, 2020, 418, pp.109645. ⟨10.1016/j.jcp.2020.109645⟩. ⟨hal-02960150⟩
S. Guo, Yongliang Feng, Jérôme Jacob, F. Renard, Pierre Sagaut. An efficient lattice Boltzmann method for compressible aerodynamics on D3Q19 lattice. Journal of Computational Physics, 2020, 418, pp.109570. ⟨10.1016/j.jcp.2020.109570⟩. ⟨hal-02960161⟩ Plus de détails...
An efficient lattice Boltzmann (LB) model relying on a hybrid recursive regularization (HRR) collision operator on D3Q19 stencil is proposed for the simulation of three-dimensional high-speed compressible flows in both subsonic and supersonic regimes. An improved thermal equilibrium distribution function on D3Q19 lattice is derived to reduce the complexity of correcting terms. A simple shock capturing scheme and an upwind biased discretization of correction terms are implemented for supersonic flows with shocks. Mass and momentum equations are recovered by an efficient streaming, collision and forcing process on D3Q19 lattice. Then a non-conservative formulation of the entropy evolution equation is used, that is solved using a finite volume method. The proposed method is assessed considering the simulation of i) 2D isentropic vortex convection, ii) 3D non-isothermal acoustic pulse, iii) 2D supersonic flow over a bump, iv) 3D shock explosion in a box, v) 2D vortex interaction with shock wave, vi) 2D laminar flows over a flat plate at Ma of 0.5, 1.0 and 1.5.
S. Guo, Yongliang Feng, Jérôme Jacob, F. Renard, Pierre Sagaut. An efficient lattice Boltzmann method for compressible aerodynamics on D3Q19 lattice. Journal of Computational Physics, 2020, 418, pp.109570. ⟨10.1016/j.jcp.2020.109570⟩. ⟨hal-02960161⟩
M. Meldi, A. Mariotti, M. Salvetti, P. Sagaut. Numerical investigation of skewed spatially evolving mixing layers. Journal of Fluid Mechanics, 2020, 897, pp.A35. ⟨10.1017/jfm.2020.407⟩. ⟨hal-03251559⟩ Plus de détails...
The sensitivity of turbulent dynamics in spatially evolving mixing layers to small skew angles is investigated via direct numerical simulation. Angle is a measure of the lack of parallelism between the two asymptotic flows, whose interaction creates the turbulent mixing region. The analysis is performed considering a large range of values of the shear intensity parameter . This two-dimensional parameter space is explored using the results of a database of 18 direct numerical simulations. Instantaneous fields as well as time-averaged quantities are investigated, highlighting important mechanisms in the emergence of turbulence and its characteristics for this class of flows. In addition, a stochastic approach is used in which and are considered as random variables with a given probability distribution. The response surfaces of flow statistics in the parameter space are built through non-intrusive generalized polynomial chaos. It is found that variations of the parameter have a primary effect on the growth of the mixing region. A secondary effect associated with is observed as well. Higher values for the skew angle are responsible for a rapid increase in growth of the inlet structures, enhancing the development of the mixing region. The impact on the turbulence features and, in particular, on the Reynolds stress tensor is also significant. A modification of the normalized diagonal components of the Reynolds stress tensor due to is observed. In addition, the interaction between the parameters and is here the governing element.
M. Meldi, A. Mariotti, M. Salvetti, P. Sagaut. Numerical investigation of skewed spatially evolving mixing layers. Journal of Fluid Mechanics, 2020, 897, pp.A35. ⟨10.1017/jfm.2020.407⟩. ⟨hal-03251559⟩
Etienne Loiseau, Simon Gsell, Aude Nommick, Charline Jomard, Delphine Gras, et al.. Active mucus–cilia hydrodynamic coupling drives self-organization of human bronchial epithelium. Nature Physics, 2020, ⟨10.1038/s41567-020-0980-z⟩. ⟨hal-02914172⟩ Plus de détails...
The respiratory tract is protected by mucus, a complex fluid transported along the epithelial surface by the coordinated beating of millions of microscopic cilia, hence the name of mucociliary clearance. Its impairment is associated with all severe chronic respiratory diseases. Yet, the relationship between ciliary density and the spatial scale of mucus transport, as well as the mechanisms that drive ciliary-beat orientations are much debated. Here, we show on polarized human bronchial epithelia that mucus swirls and circular orientational order of the underlying ciliary beats emerge and grow during ciliogenesis, until a macroscopic mucus transport is achieved for physiological ciliary densities. By establishing that the macroscopic ciliary-beat order is lost and recovered by removing and adding mucus, respectively, we demonstrate that cilia–mucus hydrodynamic interactions govern the collective dynamics of ciliary-beat directions. We propose a two-dimensional model that predicts a phase diagram of mucus transport in accordance with the experiments. This paves the way to a predictive in silico modelling of bronchial mucus transport in health and disease.
Etienne Loiseau, Simon Gsell, Aude Nommick, Charline Jomard, Delphine Gras, et al.. Active mucus–cilia hydrodynamic coupling drives self-organization of human bronchial epithelium. Nature Physics, 2020, ⟨10.1038/s41567-020-0980-z⟩. ⟨hal-02914172⟩
Jérémie Labasse, Uwe Ehrenstein, Philippe Meliga. Numerical exploration of the pitching plate parameter space with application to thrust scaling. Applied Ocean Research, 2020, 101, pp.102278. ⟨10.1016/j.apor.2020.102278⟩. ⟨hal-02903603⟩ Plus de détails...
Jérémie Labasse, Uwe Ehrenstein, Philippe Meliga. Numerical exploration of the pitching plate parameter space with application to thrust scaling. Applied Ocean Research, 2020, 101, pp.102278. ⟨10.1016/j.apor.2020.102278⟩. ⟨hal-02903603⟩
Uwe Ehrenstein, Jérémie Labasse, Philippe Meliga. Numerical exploration of the pitching plate parameter space with application to thrust scaling. Applied Ocean Research, 2020, 101, pp.102278. ⟨10.1016/j.apor.2020.102278⟩. ⟨hal-03235146⟩ Plus de détails...
The thrust performance of a two-dimensional plate pitching harmonically in a uniform flow is assessed numerically using the OpenFOAM toolbox [1]. The mesh displacement vector associated with the rigid body motion is computed as the solution of a Laplace equation with variable diffusivity, using the appropriate mesh manipulation class of the toolbox. For a Reynolds number of 2000, the accuracy of the pressure and viscous stress distributions is assessed by comparison with reference data available for an equivalent fluid configuration. The efficiency and flexibility of the solver allows exploring large ranges of the pitching parameter space, that is the pitching frequency, amplitude and pivot-point location of the pitching plate. The forces induced by the pitching motion are computed for pitching amplitudes up to 15 ∘ , for Strouhal numbers varying between 0.2 and 0.5 and for different pitch pivot points. Performing a thrust scaling analysis, a classical theoretical model for the swimming of a waving plate is reliably fitted to the numerical pressure force data. The dependence of the time averaged thrust with the pitching axis is shown to be predicted accurately by a classical potential flow formula (known as Garrick's theory) for pivot points within the front quarter of the plate. The viscous drag is computed as well for the Reynolds number 2000. The time-averaged values are shown to depend on the pitching amplitude and frequency and for instance a Blasius-type scaling, sometimes used to model the viscous drag correction for oscillating two-dimensional foils in this Reynolds number range, is not reliable.
Uwe Ehrenstein, Jérémie Labasse, Philippe Meliga. Numerical exploration of the pitching plate parameter space with application to thrust scaling. Applied Ocean Research, 2020, 101, pp.102278. ⟨10.1016/j.apor.2020.102278⟩. ⟨hal-03235146⟩
Shahram Khazaie, Régis Cottereau. Influence of local cubic anisotropy on the transition towards an equipartition regime in a 3D texture-less random elastic medium. Wave Motion, 2020, 96, pp.102574. ⟨10.1016/j.wavemoti.2020.102574⟩. ⟨hal-02566857⟩ Plus de détails...
At long lapse times in randomly fluctuating media with macroscopic isotropy (texture-less media), the energy of elastic waves is equipartitioned between compressional (P) and shear (S) waves. This property is independent of the local isotropy or anisotropy of the heterogeneous constitutive tensor and of the type of source. However the local symmetry of the constitutive tensor does influence the rate of convergence to equipartition and this paper discusses the precise influence of local anisotropy on the time required to reach equipartition. More particularly, a randomly-fluctuating medium is considered, whose behavior is statistically isotropic, and locally cubic. After calculating all the differential and total scattering cross-sections in that case, an analytical formula is derived for the rate of convergence to the equipartition regime, function of the second-order statistics of the mechanical parameter fields (bulk and shear moduli and anisotropy parameter). The local anisotropy is shown to influence strongly that transition rate, with a faster transition when the fluctuations of the anisotropy parameter are positively correlated to those of the shear modulus. A numerical model is constructed to illustrate numerically these results. Since the asymptotic regime of equipartition cannot be simulated directly because it would require too large a computational domain, boundaries are introduced and mechanical properties are chosen so as to minimize their influence on equipartition.
Shahram Khazaie, Régis Cottereau. Influence of local cubic anisotropy on the transition towards an equipartition regime in a 3D texture-less random elastic medium. Wave Motion, 2020, 96, pp.102574. ⟨10.1016/j.wavemoti.2020.102574⟩. ⟨hal-02566857⟩
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. A New Explicit Algebraic Wall Model for LES of Turbulent Flows Under Adverse Pressure Gradient. Flow, Turbulence and Combustion, 2020, ⟨10.1007/s10494-020-00181-7⟩. ⟨hal-02960184⟩ Plus de détails...
A new explicit algebraic wall law for the Large Eddy Simulation of flows with adverse pressure gradient is proposed. This new wall law, referred as adverse pressure gradient power law (APGPL), is developed starting from the power-law of Werner and Wengle (Turbulent Shear Flows, vol 8, Springer, New York, pp 155-168, 1993) in order to mimic an implicit non-equilibrium log-law based on Afzal's law (Afzal, IUTAM Symposium on Asymptotic Methods for Turbulent Shear Flows at High Reynolds Numbers, Kluwer Academic Publishers, Bochum, pp 95-118, 1996). No iterative method is needed for the evaluation of the wall shear stress from the APGPL contrary to the majority of models available in the literature. The APGPL model relies on the definition of three modes: the equilibrium power-law is used in regions of no or favourable pressure gradient, the APGPL is used in regions of adverse pressure gradient, and no wall model is used in separated flow regions. This model is assessed via Large Eddy Simulations of flows involving adverse pressure gradient and boundary layer separation using the Lattice Boltzmann Method on uniform nested grids. The flow around a clean and iced NACA23012 airfoil at Reynolds numberRe=1.88 x 10(6) and the flow over the LAGOON landing gear at Re=1.59x10(6) are considered. Results are found in good agreement with those obtained by the non-equilibrium log-law and experimental and numerical data available in the literature.
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. A New Explicit Algebraic Wall Model for LES of Turbulent Flows Under Adverse Pressure Gradient. Flow, Turbulence and Combustion, 2020, ⟨10.1007/s10494-020-00181-7⟩. ⟨hal-02960184⟩
G. Farag, S. Zhao, T. Coratger, Pierre Boivin, G. Chiavassa, et al.. A pressure-based regularized lattice-Boltzmann method for the simulation of compressible flows. Physics of Fluids, 2020, 32 (6), pp.066106. ⟨10.1063/5.0011839⟩. ⟨hal-02885427⟩ Plus de détails...
A new pressure-based Lattice-Boltzmann method (HRR-p) is proposed for the simulation of flows for Mach numbers ranging from 0 to 1.5. Compatible with nearest neighbor lattices (e.g. D3Q19), the model consists of a predictor step comparable to classical athermal Lattice-Boltzmann methods, appended with a fully local and explicit correction step for the pressure. Energy conservation-for which the Hermi-tian quadrature is not accurate enough on such lattice-is solved via a classical finite volume MUSCL-Hancock scheme based on the entropy equation. The Euler part of the model is then validated for the transport of three canonical modes (vortex, en-tropy, and acoustic propagation), while its diffusive/viscous properties are assessed via thermal Couette flow simulations. All results match the analytical solutions, with very limited dissipation. Lastly, the robustness of the method is tested in a one dimensional shock tube and a two-dimensional shock-vortex interaction.
G. Farag, S. Zhao, T. Coratger, Pierre Boivin, G. Chiavassa, et al.. A pressure-based regularized lattice-Boltzmann method for the simulation of compressible flows. Physics of Fluids, 2020, 32 (6), pp.066106. ⟨10.1063/5.0011839⟩. ⟨hal-02885427⟩
Y. Feng, S. Guo, J. Jacob, P. Sagaut. Grid refinement in the three-dimensional hybrid recursive regularized lattice Boltzmann method for compressible aerodynamics. Physical Review E , 2020, 101 (6), pp.063302. ⟨10.1103/PhysRevE.101.063302⟩. ⟨hal-03228997⟩ Plus de détails...
Grid refinement techniques are of paramount importance for computational fluid dynamics approaches relying on the use of Cartesian grids. This is especially true of solvers dedicated to aerodynamics, in which the capture of thin shear layers require the use of small cells. In this paper, a three-dimensional grid refinement technique is developed within the framework of hybrid recursive regularized lattice Boltzmann method (HRR-LBM) for compressible high-speed flows, which is an efficient collide-stream-type method on a compact D3Q19 stencil. The proposed method is successfully assessed considering several test cases, namely, an isentropic vortex propagating through transition interface, shock-vortex interaction with intersection between grid refinement interface and shock corrugation, and transonic flows over three-dimensional DLR-M6 wing with seven levels of grid refinement.
Y. Feng, S. Guo, J. Jacob, P. Sagaut. Grid refinement in the three-dimensional hybrid recursive regularized lattice Boltzmann method for compressible aerodynamics. Physical Review E , 2020, 101 (6), pp.063302. ⟨10.1103/PhysRevE.101.063302⟩. ⟨hal-03228997⟩
Y. Feng, S. Guo, J. Jacob, P. Sagaut. Grid refinement in the three-dimensional hybrid recursive regularized lattice Boltzmann method for compressible aerodynamics. Physical Review E , 2020, 101 (6), pp.063302. ⟨10.1103/PhysRevE.101.063302⟩. ⟨hal-02892273⟩ Plus de détails...
Grid refinement techniques are of paramount importance for computational fluid dynamics approaches relying on the use of Cartesian grids. This is especially true of solvers dedicated to aerodynamics, in which the capture of thin shear layers require the use of small cells. In this paper, a three-dimensional grid refinement technique is developed within the framework of hybrid recursive regularized lattice Boltzmann method (HRR-LBM) for compressible high-speed flows, which is an efficient collide-stream-type method on a compact D3Q19 stencil. The proposed method is successfully assessed considering several test cases, namely, an isentropic vortex propagating through transition interface, shock-vortex interaction with intersection between grid refinement interface and shock corrugation, and transonic flows over three-dimensional DLR-M6 wing with seven levels of grid refinement.
Y. Feng, S. Guo, J. Jacob, P. Sagaut. Grid refinement in the three-dimensional hybrid recursive regularized lattice Boltzmann method for compressible aerodynamics. Physical Review E , 2020, 101 (6), pp.063302. ⟨10.1103/PhysRevE.101.063302⟩. ⟨hal-02892273⟩
Simon Gsell, Etienne Loiseau, Umberto D’ortona, Annie Viallat, Julien Favier. Hydrodynamic model of directional ciliary-beat organization in human airways. Scientific Reports, 2020, 10 (8405), ⟨10.1038/s41598-020-64695-w⟩. ⟨hal-02614711⟩ Plus de détails...
In the lung, the airway surface is protected by mucus, whose transport and evacuation is ensured through active ciliary beating. the mechanisms governing the long-range directional organization of ciliary beats, required for effective mucus transport, are much debated. Here, we experimentally show on human bronchial epithelium reconstituted in-vitro that the dynamics of ciliary-beat orientation is closely connected to hydrodynamic effects. To examine the fundamental mechanisms of this self-organization process, we build a two-dimensional model in which the hydrodynamic coupling between cilia is provided by a streamwise-alignment rule governing the local orientation of the ciliary forcing. The model reproduces the emergence of the mucus swirls observed in the experiments. The predicted swirl sizes, which scale with the ciliary density and mucus viscosity, are in agreement with in-vitro measurements. A transition from the swirly regime to a long-range unidirectional mucus flow allowing effective clearance occurs at high ciliary density and high mucus viscosity. In the latter case, the mucus flow tends to spontaneously align with the bronchus axis due to hydrodynamic effects.
Simon Gsell, Etienne Loiseau, Umberto D’ortona, Annie Viallat, Julien Favier. Hydrodynamic model of directional ciliary-beat organization in human airways. Scientific Reports, 2020, 10 (8405), ⟨10.1038/s41598-020-64695-w⟩. ⟨hal-02614711⟩
Elena Alekseenko, Bernard Roux. Risk of wind-driven resuspension and transport of contaminated sediments in a narrow marine channel confluencing a wide lagoon. Estuarine, Coastal and Shelf Science, 2020, 237, pp.106649. ⟨10.1016/j.ecss.2020.106649⟩. ⟨hal-03251615⟩ Plus de détails...
This work concerns the wind-driven resuspension in a narrow marine channel and the risk of transport of contaminated bottom sediments in a wide brackish lagoon in the context of a planned anthropogenic infrastructure (with forced convection, by pumping sea water). It is based on the modelling and 3D numerical simulation of salinity, current distributions and bottom shear stress (BSS). The goal is to demonstrate that, even for narrow channels of a few tens of meter of width, a wind of 10-20 m/s is sufficient to create intensive currents, to resuspend muddy bottom sediments and transport polluted sediments downstream. Several model scenarios are considered for such wind speeds in two dominant and opposite wind directions, for a channel whose bottom sediments are mainly constituted of fine particles, typically 85% of mud and 15% of fine sand. It is known that finer sediments usually play an important role to transport contaminants (due to larger surface area of smaller particles). Our main results concern the bottom shear stress along such a long and narrow channel; namely the Rove channel which confluences the Etang de Berre lagoon, and for which a project of forced current circulation is planned by pumping sea water. Our numerical results show that the mobility threshold can be easily overpassed for the muddy sediments in the Rove channel. For a bottom roughness of 5 μm (coarse silt) and a wind speed of 20 m/s, BSS can reach 0.18 N/m 2 for the N-NW wind in the median part of the channel, and even 0.21 N/m 2 in one enlargement for the S-SE wind, while BSS cr is about 0.1 N/m 2. We conclude that these local winds can permit floc erosion and even surface erosion of fine sediments in the Rove channel. Concerning the resuspension of muddy sediments, our results are consistent with the experimental study presented by Carlin et al. (2016) for a windy shallow lagoon. They are also consistent with the conclusion of Mengual et al. (2017), from erodimetry experiment for estuarine sediments, that the sediment behaves like a pure mud if the percentage of the mud fraction is more than 70%, and that the critical BSS for mobility of such bed sediments is of the order of 0.1 N/m 2. Such a lower critical BSS when the mixture is muddier is opposite to trends most often published.
Elena Alekseenko, Bernard Roux. Risk of wind-driven resuspension and transport of contaminated sediments in a narrow marine channel confluencing a wide lagoon. Estuarine, Coastal and Shelf Science, 2020, 237, pp.106649. ⟨10.1016/j.ecss.2020.106649⟩. ⟨hal-03251615⟩
Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. Consistent vortex initialization for the athermal lattice Boltzmann method. Physical Review E , 2020, 101 (4), ⟨10.1103/PhysRevE.101.043306⟩. ⟨hal-02892501⟩ Plus de détails...
A barotropic counterpart of the well-known convected vortex test case is rigorously derived from the Euler equations along with an athermal equation of state. Starting from a given velocity distribution corresponding to an intended flow recirculation, the athermal counterpart of the Euler equations are solved to obtain a consistent density field. The present initialization is assessed on a standard lattice Boltzmann solver based on the D2Q9 lattice. Compared to the usual isentropic initialization, a much lower spurious relaxation toward the targeted solution is observed, which is due to the spatial resolution rather than approximated macroscopic quantities. The amplitude of the spurious waves can be further reduced by including an off-equilibrium part in the initial distribution functions.
Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. Consistent vortex initialization for the athermal lattice Boltzmann method. Physical Review E , 2020, 101 (4), ⟨10.1103/PhysRevE.101.043306⟩. ⟨hal-02892501⟩
Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. Consistent vortex initialization for the athermal lattice Boltzmann method. Physical Review E , 2020, 101 (4), ⟨10.1103/PhysRevE.101.043306⟩. ⟨hal-03229006⟩ Plus de détails...
A barotropic counterpart of the well-known convected vortex test case is rigorously derived from the Euler equations along with an athermal equation of state. Starting from a given velocity distribution corresponding to an intended flow recirculation, the athermal counterpart of the Euler equations are solved to obtain a consistent density field. The present initialization is assessed on a standard lattice Boltzmann solver based on the D2Q9 lattice. Compared to the usual isentropic initialization, a much lower spurious relaxation toward the targeted solution is observed, which is due to the spatial resolution rather than approximated macroscopic quantities. The amplitude of the spurious waves can be further reduced by including an off-equilibrium part in the initial distribution functions.
Gauthier Wissocq, Jean-François Boussuge, Pierre Sagaut. Consistent vortex initialization for the athermal lattice Boltzmann method. Physical Review E , 2020, 101 (4), ⟨10.1103/PhysRevE.101.043306⟩. ⟨hal-03229006⟩
T. Lyubimova, A. Lepikhin, Ya. Parshakova, C. Gualtieri, S. Lane, et al.. Influence of Hydrodynamic Regimes on Mixing of Waters of Confluent Rivers. Journal of Applied Mechanics and Technical Physics, 2020, 60 (7), pp.1220-1227. ⟨10.1134/S0021894419070083⟩. ⟨hal-02989585⟩ Plus de détails...
At present, a significant weakening of the intensity of transverse mixing at the confluence of large rivers, which is observed in a number of cases, is widely discussed. Since the observed features of the confluence of large watercourses are not only of research interest but also of significant economic importance associated with the characteristics of water management at these water bodies, a large number of works are devoted to their study. Water resources management requires measures for the organization of water use which can be rational only under the understanding of processes occurring in water basins. To explain the phenomenon of suppression of the transverse mixing, which is interesting and important from the point of view of ecology, a wide range of hypotheses is proposed, up to the negation of turbulence in rivers. One of the possible mechanisms for explaining the suppression of transversal mixing can be the presence of transverse circulation manifesting itself as Prandtl’s secondary flows of the second kind. The characteristic velocity of these circulation flows is very small and difficult to measure directly by instruments; however, in our opinion, they can significantly complicate the transverse mixing at the confluence. The proposed hypothesis is tested in computational experiments in the framework of the three-dimensional formulation for dimensions of a real water object at the mouth of the Vishera River where it meets the Kama. Calculations demonstrate that, at sufficiently large flow rates, the two waters practically do not mix in the horizontal direction throughout the depth over long distances from the confluence. It has been found that a two-vortex flow is formed downstream the confluence, which just attenuates the mixing; the fluid motion in the vortices is such that, near the free surface, the fluid moves from the banks to the middle of the riverbed.
T. Lyubimova, A. Lepikhin, Ya. Parshakova, C. Gualtieri, S. Lane, et al.. Influence of Hydrodynamic Regimes on Mixing of Waters of Confluent Rivers. Journal of Applied Mechanics and Technical Physics, 2020, 60 (7), pp.1220-1227. ⟨10.1134/S0021894419070083⟩. ⟨hal-02989585⟩
Journal: Journal of Applied Mechanics and Technical Physics
The lattice Boltzmann method often involves small numerical time steps due to the acoustic scaling (i.e., scaling between time step and grid size) inherent to the method. In this work, a second-order dual-time-stepping lattice Boltzmann method is proposed in order to avoid any time-step restriction. The implementation of the dual time stepping is based on an external source in the lattice Boltzmann equation, related to the time derivatives of the macroscopic flow quantities. Each time step is treated as a pseudosteady problem. The convergence rate of the steady lattice Boltzmann solver is improved by implementing a multigrid method. The developed solver is based on a two-relaxation time model coupled to an immersed-boundary method. The reliability of the method is demonstrated for steady and unsteady laminar flows past a circular cylinder, either fixed or towed in the computational domain. In the steady-flow case, the multigrid method drastically increases the convergence rate of the lattice Boltzmann method. The dual-time-stepping method is able to accurately reproduce the unsteady flows. The physical time step can be freely adjusted; its effect on the simulation cost is linear, while its impact on the accuracy follows a second-order trend. Two major advantages arise from this feature. (i) Simulation speed-up can be achieved by increasing the time step while conserving a reasonable accuracy. A speed-up of 4 is achieved for the unsteady flow past a fixed cylinder, and higher speed-ups are expected for configurations involving slower flow variations. Significant additional speed-up can also be achieved by accelerating transients. (ii) The choice of the time step allows us to alter the range of simulated timescales. In particular, increasing the time step results in the filtering of undesired pressure waves induced by sharp geometries or rapid temporal variations, without altering the main flow dynamics. These features may be critical to improve the efficiency and range of applicability of the lattice Boltzmann method.
Simon Gsell, Umberto d'Ortona, Julien Favier. Multigrid dual-time-stepping lattice Boltzmann method. Physical Review E , 2020, 101 (2), ⟨10.1103/PhysRevE.101.023309⟩. ⟨hal-02573156⟩
T. P Lyubimova, A. P Lepikhin, Ya N Parshakova, C. Gualtieri, S. Lane, et al.. Influence of Hydrodynamic Regimes on Mixing of Waters of Confluent Rivers. Journal of Applied Mechanics and Technical Physics, 2020, 60 (7), pp.1220-1227. ⟨10.1134/S0021894419070083⟩. ⟨hal-03231839⟩ Plus de détails...
At present, a significant weakening of the intensity of transverse mixing at the confluence of large rivers, which is observed in a number of cases, is widely discussed. Since the observed features of the confluence of large watercourses are not only of research interest but also of significant economic importance associated with the characteristics of water management at these water bodies, a large number of works are devoted to their study. Water resources management requires measures for the organization of water use which can be rational only under the understanding of processes occurring in water basins. To explain the phenomenon of suppression of the transverse mixing, which is interesting and important from the point of view of ecology, a wide range of hypotheses is proposed, up to the negation of turbulence in rivers. One of the possible mechanisms for explaining the suppression of transversal mixing can be the presence of transverse circulation manifesting itself as Prandtl’s secondary flows of the second kind. The characteristic velocity of these circulation flows is very small and difficult to measure directly by instruments; however, in our opinion, they can significantly complicate the transverse mixing at the confluence. The proposed hypothesis is tested in computational experiments in the framework of the three-dimensional formulation for dimensions of a real water object at the mouth of the Vishera River where it meets the Kama. Calculations demonstrate that, at sufficiently large flow rates, the two waters practically do not mix in the horizontal direction throughout the depth over long distances from the confluence. It has been found that a two-vortex flow is formed downstream the confluence, which just attenuates the mixing; the fluid motion in the vortices is such that, near the free surface, the fluid moves from the banks to the middle of the riverbed.
T. P Lyubimova, A. P Lepikhin, Ya N Parshakova, C. Gualtieri, S. Lane, et al.. Influence of Hydrodynamic Regimes on Mixing of Waters of Confluent Rivers. Journal of Applied Mechanics and Technical Physics, 2020, 60 (7), pp.1220-1227. ⟨10.1134/S0021894419070083⟩. ⟨hal-03231839⟩
Journal: Journal of Applied Mechanics and Technical Physics
Christophe Friess, Lars Davidson. A formulation of PANS capable of mimicking IDDES. International Journal of Heat and Fluid Flow, 2020, 86, pp.108666. ⟨10.1016/j.ijheatfluidflow.2020.108666⟩. ⟨hal-03232146⟩ Plus de détails...
The partially averaged Navier-Stokes (PANS) model, proposed in Girimaji (2006), allows to simulate turbulent flows either in RANS, LES or DNS mode. The PANS model includes f k which denotes the ratio of modeled to total kinetic energy. In RANS, f k = 1 while in DNS it tends to zero. In the present study we propose an improved formulation for f k based on the H-equivalence introduced by Friess et al. (2015). In this formulation the expression of f k is derived to mimic Improved Delayed Detached Eddy Simulation (IDDES). This new formulation behaves in a very similar way as IDDES, even though the two formulations use different mechanisms to separate modeled and resolved scales. They show very similar performance in separated flows as well as in attached boundary layers. In particular, the novel formulation is able to (i) treat attached boundary layers as properly as IDDES, and (ii) "detect" laminar initial/boundary conditions, in which case it enforces RANS mode. Furthermore, it is found that the new formulation is numerically more stable than IDDES.
Christophe Friess, Lars Davidson. A formulation of PANS capable of mimicking IDDES. International Journal of Heat and Fluid Flow, 2020, 86, pp.108666. ⟨10.1016/j.ijheatfluidflow.2020.108666⟩. ⟨hal-03232146⟩
Journal: International Journal of Heat and Fluid Flow
M. Tayyab, S. Zhao, Y. Feng, Pierre Boivin. Hybrid regularized Lattice-Boltzmann modelling of premixed and non-premixed combustion processes. Combustion and Flame, 2020, 211, pp.173-184. ⟨10.1016/j.combustflame.2019.09.029⟩. ⟨hal-02346556⟩ Plus de détails...
A Lattice-Boltzmann model for low-Mach reactive flows is presented, built upon our recently published model (Comb & Flame, 196, 2018). The approach is hybrid and couples a Lattice-Boltzmann solver for the resolution of mass and momentum conservation and a finite difference solver for the energy and species conservation. Having lifted the constant thermodynamic and transport properties assumptions, the model presented now fully accounts for the classical reactive flow thermodynamic closure: each component is assigned NASA coefficients for calculating its thermodynamic properties. A temperature-dependent viscosity is considered, from which are deduced thermo-diffusive properties via specification of Prandtl and component-specific Schmidt numbers. Another major improvement from our previous contribution is the derivation of an advanced collision kernel compatible of multi-component reactive flows stable in high shear flows. Validation is carried out first on premixed configurations, through simulation of the planar freely propagating flame, the growth of the associated Darrieus-Landau instability and three regimes of flame-vortex interaction. A double shear layer test case including a flow-stabilized diffusion flame is then presented and results are compared with DNS simulations, showing excellent agreement.
M. Tayyab, S. Zhao, Y. Feng, Pierre Boivin. Hybrid regularized Lattice-Boltzmann modelling of premixed and non-premixed combustion processes. Combustion and Flame, 2020, 211, pp.173-184. ⟨10.1016/j.combustflame.2019.09.029⟩. ⟨hal-02346556⟩
T. Cartier-Michaud, D. Galassi, Ph Ghendrih, P. Tamain, F. Schwander, et al.. A posteriori error estimate in fluid simulations of turbulent edge plasmas for magnetic fusion in tokamak using the data mining iPoPe method. Physics of Plasmas, 2020. ⟨hal-02613800⟩ Plus de détails...
Progressing towards more reliable numerical solutions in the simulation of plasma for magnetic confinement fusion has become a critical issue for the success of the ITER operation. This requires developing rigorous and efficient methods of verification of the numerical simulations in any relevant flow regimes of the operation. The paper introduces a new formulation of the PoPe 1 method, namely the independent Projection on Proper elements method (iPoPe) to quantify the numerical error by performing a data-driven identification of the mathematical model from the simulation outputs. Based on a statistical postprocessing of the outputs database, the method provides a measure of the error by estimating the distance between the (numerical) effective and (analytical) theoretical weights of each operator implemented in the mathematical model. The efficiency of the present method is illustrated on turbulent edge plasma simulations based on a drift-reduced Braginskii fluid model in realistic magnetic geometries. Results show the effective order of the numerical method in these multiscale flow regimes as well as the values of the plasma parameters which can be safely simulated with respect to a given discretization. In this sense, the method goes one step further than the Method of Manufactured Solution (MMS 2-4), recently introduced in fusion, and provides an efficient verification procedure of the numerical simulations in any regimes, including turbulent ones that could be generalized to other scientific domains.
T. Cartier-Michaud, D. Galassi, Ph Ghendrih, P. Tamain, F. Schwander, et al.. A posteriori error estimate in fluid simulations of turbulent edge plasmas for magnetic fusion in tokamak using the data mining iPoPe method. Physics of Plasmas, 2020. ⟨hal-02613800⟩
S. Guo, Yongliang Feng, Jérôme Jacob, F. Renard, Pierre Sagaut. An efficient lattice Boltzmann method for compressible aerodynamics on D3Q19 lattice. Journal of Computational Physics, 2020, 418, pp.109570. ⟨10.1016/j.jcp.2020.109570⟩. ⟨hal-03232070⟩ Plus de détails...
An efficient lattice Boltzmann (LB) model relying on a hybrid recursive regularization (HRR) collision operator on D3Q19 stencil is proposed for the simulation of three-dimensional high-speed compressible flows in both subsonic and supersonic regimes. An improved thermal equilibrium distribution function on D3Q19 lattice is derived to reduce the complexity of correcting terms. A simple shock capturing scheme and an upwind biased discretization of correction terms are implemented for supersonic flows with shocks. Mass and momentum equations are recovered by an efficient streaming, collision and forcing process on D3Q19 lattice. Then a non-conservative formulation of the entropy evolution equation is used, that is solved using a finite volume method. The proposed method is assessed considering the simulation of i) 2D isentropic vortex convection, ii) 3D non-isothermal acoustic pulse, iii) 2D supersonic flow over a bump, iv) 3D shock explosion in a box, v) 2D vortex interaction with shock wave, vi) 2D laminar flows over a flat plate at Ma of 0.5, 1.0 and 1.5.
S. Guo, Yongliang Feng, Jérôme Jacob, F. Renard, Pierre Sagaut. An efficient lattice Boltzmann method for compressible aerodynamics on D3Q19 lattice. Journal of Computational Physics, 2020, 418, pp.109570. ⟨10.1016/j.jcp.2020.109570⟩. ⟨hal-03232070⟩
G Giorgiani, H. Bufferand, F. Schwander, E. Serre, P. Tamain. A high-order non field-aligned approach for the discretization of strongly anistropic diffusion operators in magnetic fusion. Computer Physics Communications, 2020, 254, pp.107375. ⟨10.1016/j.cpc.2020.107375⟩. ⟨hal-02613709⟩ Plus de détails...
In this work we present a hybrid discontinuous Galerkin scheme for the solution of extremely anisotropic diffusion problems arising in magnetized plasmas for fusion applications. Unstructured meshes, non-aligned with respect to the dominant diffusion direction, allow an unequalled flexibility in discretizing geometries of any shape, but may lead to spurious numerical diffusion. Curved triangles or quadrangles are used to discretize the poloidal plane of the machine, while a structured discretization is used in the toroidal direction. The proper design of the numerical fluxes guarantees the correct convergence order at any anisotropy level. Computations performed on well-designed 2D and 3D numerical tests show that non-aligned discretizations are able to provide spurious diffusion free solutions as long as high-order interpolations are used. Introducing an explicit measure of the numerical diffusion, a careful investigation is carried out showing an exponential increase of this latest with respect to the non-alignment of the mesh with the diffusion direction, as well as an exponential decrease with the polynomial degree of interpolation. A brief assessment of the method with respect to two finite-difference schemes using non-aligned discretization, but classically used in fusion modeling, is also presented.
G Giorgiani, H. Bufferand, F. Schwander, E. Serre, P. Tamain. A high-order non field-aligned approach for the discretization of strongly anistropic diffusion operators in magnetic fusion. Computer Physics Communications, 2020, 254, pp.107375. ⟨10.1016/j.cpc.2020.107375⟩. ⟨hal-02613709⟩
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. A New Explicit Algebraic Wall Model for LES of Turbulent Flows Under Adverse Pressure Gradient. Flow, Turbulence and Combustion, 2020, 106 (1), pp.1-35. ⟨10.1007/s10494-020-00181-7⟩. ⟨hal-03231798⟩ Plus de détails...
A new explicit algebraic wall law for the Large Eddy Simulation of flows with adverse pressure gradient is proposed. This new wall law, referred as adverse pressure gradient power law (APGPL), is developed starting from the power-law of Werner and Wengle (Turbulent Shear Flows, vol 8, Springer, New York, pp 155-168, 1993) in order to mimic an implicit non-equilibrium log-law based on Afzal's law (Afzal, IUTAM Symposium on Asymptotic Methods for Turbulent Shear Flows at High Reynolds Numbers, Kluwer Academic Publishers, Bochum, pp 95-118, 1996). No iterative method is needed for the evaluation of the wall shear stress from the APGPL contrary to the majority of models available in the literature. The APGPL model relies on the definition of three modes: the equilibrium power-law is used in regions of no or favourable pressure gradient, the APGPL is used in regions of adverse pressure gradient, and no wall model is used in separated flow regions. This model is assessed via Large Eddy Simulations of flows involving adverse pressure gradient and boundary layer separation using the Lattice Boltzmann Method on uniform nested grids. The flow around a clean and iced NACA23012 airfoil at Reynolds numberRe=1.88 x 10(6) and the flow over the LAGOON landing gear at Re=1.59x10(6) are considered. Results are found in good agreement with those obtained by the non-equilibrium log-law and experimental and numerical data available in the literature.
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. A New Explicit Algebraic Wall Model for LES of Turbulent Flows Under Adverse Pressure Gradient. Flow, Turbulence and Combustion, 2020, 106 (1), pp.1-35. ⟨10.1007/s10494-020-00181-7⟩. ⟨hal-03231798⟩
A Gineau, E. Longatte, D. Lucor, P. Sagaut. Macroscopic model of fluid structure interaction in cylinder arrangement using theory of mixture. Computers and Fluids, 2020, 202, pp.104499. ⟨10.1016/j.compfluid.2020.104499⟩. ⟨hal-03251640⟩ Plus de détails...
In the framework of the theory of mixture, the dynamic behaviour of solid cylinder bundles submitted to external hydrodynamic load exerted by surrounding viscous fluid flow is described. Mass conservation and momentum balance formulated on an elementary domain made of a given volume of mixture give rise to a system of coupled equations governing solid space-averaged displacement, fluid velocity and pressure provided that near-wall hydrodynamic load on each vibrating cylinder is expressed as a function of both fluid and solid space-averaged velocity fields. Then, the ability of the macroscopic model to reproduce over time an averaged flow surrounding vibrating cylinders in a large array in the context of small magnitude displacements is pointed out. Numerical solutions obtained on a two-dimensional configuration involving an array of several hundreds of cylinders subjected to an impulsional load are compared to those provided by averaged well-resolved microscopic-scale solutions. The relative error is less than 3% in terms of displacement magnitude and 5% for frequency delay. The proposed macroscopic model does not include any assumption on relative effect contributions to mechanical exchanges occurring in the full domain. Therefore it features interesting properties in terms of fluid solid interaction prediction capabilities. Moreover it contributes to a significant gain in terms of computational time and resources. Further developments are now required in order to extent the formulation to large magnitude displacements including three-dimensional effects. This could be recommended for investigations on fuel assembly vibration risk assessment in Pressure Water, Fast Breeder reactors at a whole core scale or any other large-scale mechanical system involving some kind of periodic geometry.
A Gineau, E. Longatte, D. Lucor, P. Sagaut. Macroscopic model of fluid structure interaction in cylinder arrangement using theory of mixture. Computers and Fluids, 2020, 202, pp.104499. ⟨10.1016/j.compfluid.2020.104499⟩. ⟨hal-03251640⟩
Yongliang Feng, S. Guo, Jérôme Jacob, Pierre Sagaut. Solid wall and open boundary conditions in hybrid recursive regularized lattice Boltzmann method for compressible flows. Physics of Fluids, 2019, 31 (12), pp.126103. ⟨10.1063/1.5129138⟩. ⟨hal-02467965⟩ Plus de détails...
Complex geometries and open boundaries have been intensively studied in the nearly incompressible lattice Boltzmann method (LBM) framework. Therefore, only few boundary conditions for the high speed fully compressible LBM have been proposed. This paper deals with the definition of efficient boundary conditions for the compressible LBM methods, with the emphasis put on the newly proposed hybrid recursive regularized D3Q19 LBM (HRR-LBM) with applications to compressible aerodynamics. The straightforward simple extrapolation-based far-field boundary conditions, the characteristic boundary conditions, and the absorbing sponge layer approach are extended and estimated in the HRR-LBM for the choice of open boundaries. Moreover, a cut-cell type approach to handle the immersed solid is proposed to model both slip and no-slip wall boundary conditions with either isothermal or adiabatic behavior. The proposed implementations are assessed considering the simulation of (i) isentropic vortex convection with subsonic to supersonic inflow and outflow conditions, (ii) two-dimensional (2D) compressible mixing layer, (iii) steady inviscid transonic flow over a National Advisory Committee for Aeronautics (NACA) 0012 airfoil, (iv) unsteady viscous transonic flow over a NACA 0012 airfoil, and (v) three-dimensional (3D) transonic flows over a German Aerospace Center (DLR) F6 full aircraft configuration.
Yongliang Feng, S. Guo, Jérôme Jacob, Pierre Sagaut. Solid wall and open boundary conditions in hybrid recursive regularized lattice Boltzmann method for compressible flows. Physics of Fluids, 2019, 31 (12), pp.126103. ⟨10.1063/1.5129138⟩. ⟨hal-02467965⟩
S. Kahn, C. Reux, J.-F Artaud, G Aiello, J.-B Blanchard, et al.. Sensitivity analysis of fusion power plant designs using the SYCOMORE system code. Nuclear Fusion, 2019, 60 (1), pp.016015. ⟨10.1088/1741-4326/ab4879⟩. ⟨cea-02426430⟩ Plus de détails...
The next step after ITER is the demonstration of stable electricity production with a fusion reactor. Key design performances will have to be met by the corresponding power plant demonstrator (DEMO), fulfilling a large number of constraints. System codes such as SYCOMORE, by simulating all the fusion power plant subsystems , address those questions. To be able to perform design optimizations, simplified models relying on physical and technological assumptions have to be used, resulting in a large number of input parameters. As these parameters are not always exactly known, the impact of their associated uncertainties on final design performances has to be evaluated. Sensitivity methods, by measuring the relative influence of inputs on the figures of merit of the design, allow to select the dominant parameters. This information helps the search for optimal working points, guides the priority for technical improvements and finally allows selecting meaningful inputs for uncertainty propagation. A full set of sensitivity methods and their application on a ITER and a DEMO design will be presented, discussing both the statistical methods behaviors and the physical results. Plasma shape parameters (minor radius and plasma elongations) share half of the net electricity power sensitivity for the DEMO 2015 design while the toroidal magnetic field and the 95 % safety factor are responsible for 23% and 17% of the electric power sensitivity, respectively. The plasma minor radius is responsible for 45% of the pulse duration sensitivity for the DEMO 2015 design, while plasma physics parameters drive ∼ 37% of the pulse duration sensitivity.
S. Kahn, C. Reux, J.-F Artaud, G Aiello, J.-B Blanchard, et al.. Sensitivity analysis of fusion power plant designs using the SYCOMORE system code. Nuclear Fusion, 2019, 60 (1), pp.016015. ⟨10.1088/1741-4326/ab4879⟩. ⟨cea-02426430⟩
R. Mao, N. Fedorczak, G. Ciraolo, H. Bufferand, Y. Marandet, et al.. Impact of an alternative divertor configuration on plasma detachment: pure deuterium simulations using the SOLEDGE2D-EIRENE edge transport code for HL-2M scenarios. Nuclear Fusion, 2019, 59 (10), pp.106019. ⟨10.1088/1741-4326/ab3005⟩. ⟨hal-02468022⟩ Plus de détails...
The SOLEDGE-EIRENE edge plasma code provides solutions for particle and energy transport in the plasma edge within complex and realistic 2D geometries (Bufferand et al 2015 Nucl. Fusion 55 053025). In this work, divertor detachment is simulated on HL-2M alternative magnetic configurations in pure deuterium plasma. Starting from a typical HL-2M low single-null configuration, the snowflake plus (SF+) and snowflake minus (SF-) configurations have then been investigated. Detachment of the outer target is studied in these configurations during plasma density ramps controlled by a fueling source, with constant input power and constant radial transport coefficients. Some typical characteristics of detachment, like threshold, depth and upstream window of detachment are investigated. In the three geometries, detachment onset and evolution with upstream plasma density is characterized by the gradual displacement of a radiation front from the outer target to the main X-point, as observed in experiments. It is found that, whatever the detachment in terms of particle, momentum or power dissipation, the detachment threshold is dominated primarily by the geometrical structure of the divertor plate and does not exhibit dependence on the magnetic configuration of the diverted plasma volume. In particular, the parallel connection length in the divertor is not found to affect the detachment threshold, in contrast with simple expectations from the two-point model, but in agreement with experimental findings.
R. Mao, N. Fedorczak, G. Ciraolo, H. Bufferand, Y. Marandet, et al.. Impact of an alternative divertor configuration on plasma detachment: pure deuterium simulations using the SOLEDGE2D-EIRENE edge transport code for HL-2M scenarios. Nuclear Fusion, 2019, 59 (10), pp.106019. ⟨10.1088/1741-4326/ab3005⟩. ⟨hal-02468022⟩
The coordinated beating of epithelial cilia in human lungs is a fascinating problem from the hydrodynamics perspective. The phase lag between neighboring cilia is able to generate collective cilia motions, known as metachronal waves. Different kinds of waves can occur, antiplectic or symplectic, depending on the direction of the wave with respect to the flow direction. It is shown here, using a coupled lattice Boltzmann-immersed boundary solver, that the key mechanism responsible for their transport efficiency is a blowing-suction effect that displaces the interface between the periciliary liquid and the mucus phase. The contribution of this mechanism on the average flow generated by the cilia is compared to the contribution of the lubrication effect. The results reveal that the interface displacement is the main mechanism responsible for the better efficiency of antiplectic metachronal waves over symplectic ones to transport bronchial mucus. The conclusions drawn here can be extended to any two-layer fluid configuration having different viscosities, and put into motion by cilia-shaped or comb-plate structures, having a back-and-forth motion with phase lags.
Sylvain Chateau, Julien Favier, Sébastien Poncet, Umberto d'Ortona. Why antiplectic metachronal cilia waves are optimal to transport bronchial mucus. Physical Review E , 2019, 100 (4), pp.042405. ⟨10.1103/PhysRevE.100.042405⟩. ⟨hal-02468006⟩
H. Anand, R.A. Pitts, P.C. de Vries, J.A. Snipes, F. Nespoli, et al.. Experimental implementation of a real-time power flux estimator for the ITER first wall on the TCV tokamak. Fusion Engineering and Design, 2019, 147, pp.111242. ⟨10.1016/j.fusengdes.2019.111242⟩. ⟨hal-02468015⟩ Plus de détails...
A control-oriented approach to the monitoring of wall power flux densities on ITER has been successfully developed. It is based on real-time equilibrium reconstruction in 2-D which is then used to describe the deposited heat flux as a poloidal flux function with user specified parameters for the power exhausted into the scrape-off layer (SOL) and the SOL heat flux width. To account for the real 3-D geometry of the plasma-facing components (PFC), appropriate weighting factors are derived from magnetic field line tracing in 3-D. Integration of the 3-D effect is performed with a new GUI-based software environment, SMITER, incorporating a field line tracer and permitting import and meshing of PFC CAD models. The paper discusses the experimental demonstration of the model-based wall heat flux algorithm on the TCV tokamak, reporting on the benchmarking of the new code package, SMITER against infra-red camera heat flux measurements and the derivation of the component shaping weighting factors. A comparison of the real-time estimation of the peak power flux and its spatial location against the off-line infra-red measurement for limiter plasma configurations is presented.
H. Anand, R.A. Pitts, P.C. de Vries, J.A. Snipes, F. Nespoli, et al.. Experimental implementation of a real-time power flux estimator for the ITER first wall on the TCV tokamak. Fusion Engineering and Design, 2019, 147, pp.111242. ⟨10.1016/j.fusengdes.2019.111242⟩. ⟨hal-02468015⟩
F. Nespoli, P. Tamain, N. Fedorczak, G. Ciraolo, D. Galassi, et al.. 3D structure and dynamics of filaments in turbulence simulations of WEST diverted plasmas. Nuclear Fusion, 2019. ⟨hal-02364554⟩ Plus de détails...
We study the effect of a diverted magnetic geometry on edge plasma turbulence, focusing on the three-dimensional structure and dynamics of filaments, also called blobs, in simulations of the WEST tokamak, featuring a primary and secondary X-point. For this purpose, in addition to classical analysis techniques, we apply here a novel fully 3D Blob Recognition And Tracking (BRAT) algorithm, allowing for the first time to resolve the three-dimensional structure and dynamics of the blobs in a turbulent 3D plasma featuring a realistic magnetic geometry. The results are tested against existing theoretical scalings of blob velocity [Myra et al, Physics of Plasmas 2006]. The complementary analysis of the 3D structure of the filaments shows how they disconnect from the divertor plate in the vicinity of the X-points, leading to a transition from a sheath-connected regime to the ideal-interchange one. Furthermore, the numerical results show non-negligible effects of the turbulent background plasma: approximately half of the detected filaments are involved in mutual interactions, eventually resulting in negative radial velocities, and a fraction of the filaments is generated by turbulence directly below the X-point.
F. Nespoli, P. Tamain, N. Fedorczak, G. Ciraolo, D. Galassi, et al.. 3D structure and dynamics of filaments in turbulence simulations of WEST diverted plasmas. Nuclear Fusion, 2019. ⟨hal-02364554⟩
Simon Gsell, Umberto d'Ortona, Julien Favier. Explicit and viscosity-independent immersed-boundary scheme for the lattice Boltzmann method. Physical Review E , 2019, 100 (3), ⟨10.1103/PhysRevE.100.033306⟩. ⟨hal-02339475⟩ Plus de détails...
Viscosity independence of lattice-Boltzmann methods is a crucial issue to ensure the physical relevancy of the predicted macroscopic flows over large ranges of physical parameters. The immersed-boundary (IB) method, a powerful tool that allows one to immerse arbitrary-shaped, moving, and deformable bodies in the flow, suffers from a boundary-slip error that increases as a function of the fluid viscosity, substantially limiting its range of application. In addition, low fluid viscosities may result in spurious oscillations of the macroscopic quantities in the vicinity of the immersed boundary. In this work, it is shown mathematically that the standard IB method is indeed not able to reproduce the scaling properties of the macroscopic solution, leading to a viscosity-related error on the computed IB force. The analysis allows us to propose a simple correction of the IB scheme that is local, straightforward and does not involve additional computational time. The derived method is implemented in a two-relaxation-time D2Q9 lattice-Boltzmann solver, applied to several physical configurations, namely, the Poiseuille flow, the flow around a cylinder towed in still fluid, and the flow around a cylinder oscillating in still fluid, and compared to a noncorrected immersed-boundary method. The proposed correction leads to a major improvement of the viscosity independence of the solver over a wide range of relaxation times (from 0.5001 to 50), including the correction of the boundary-slip error and the suppression of the spurious oscillations. This improvement may considerably extend the range of application of the IB lattice-Boltzmann method, in particular providing a robust tool for the numerical analysis of physical problems involving fluids of varying viscosity interacting with solid geometries.
Simon Gsell, Umberto d'Ortona, Julien Favier. Explicit and viscosity-independent immersed-boundary scheme for the lattice Boltzmann method. Physical Review E , 2019, 100 (3), ⟨10.1103/PhysRevE.100.033306⟩. ⟨hal-02339475⟩
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows. Physical Review E , 2019. ⟨hal-02265484⟩ Plus de détails...
An extended version of the hybrid recursive regularized Lattice-Boltzmann model which incorporates external force is developed to simulate humid air flows with phase change mechanisms under the Boussinesq approximation. Mass and momentum conservation equations are solved by a regu-larized lattice Boltzmann approach well suited for high Reynolds number flows, whereas the energy and humidity related equations are solved by a finite volume approach. Two options are investigated to account for cloud formation in atmospheric flow simulations. The first option considers a single conservation equation for total water and an appropriate invariant variable of temperature. In the other approach, liquid and vapor are considered via two separated equations, and phase transition is accounted for via a relaxation procedure. The obtained models are then systematically validated on four well-established benchmark problems including a double diffusive Rayleigh Bénard convection of humid air, 2D and 3D thermal moist rising bubble under convective atmospheric environment as well as a shallow cumulus convection in framework of large-eddy simulation.
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized lattice Boltzmann simulation of humid air with application to meteorological flows. Physical Review E , 2019. ⟨hal-02265484⟩
G. Ciraolo, A. Thin, H. Bufferand, J. Bucalossi, N. Fedorczak, et al.. First modeling of strongly radiating WEST plasmas with SOLEDGE-EIRENE. Nuclear Materials and Energy, 2019, 20, pp.100685. ⟨10.1016/j.nme.2019.100685⟩. ⟨hal-02468035⟩ Plus de détails...
We present first results of SOLEDGE-EIRENE modeling a strongly radiating plasma in the WEST tokamak. Using measurements from a reciprocating Langmuir probe we have determined the SOLEDGE input parameters, i.e. separatrix density at outboard midplane and radial transport coefficients typical of L-mode plasma. We have performed deuterium plasma simulations with presence of oxygen, injected from the core boundary into the simulation domain. The comparison between the radiated power measured from the bolometry in the divertor region and the one computed from SOLEDGE simulations seems to indicate a concentration of oxygen of about 2%. Moreover we have obtained good agreement between simulation results and experimental measurements on electron density and electron temperature profiles at the outer strike point. First qualitative analysis of spectroscopic synthetic diagnostic on D-alpha signals is also presented.
G. Ciraolo, A. Thin, H. Bufferand, J. Bucalossi, N. Fedorczak, et al.. First modeling of strongly radiating WEST plasmas with SOLEDGE-EIRENE. Nuclear Materials and Energy, 2019, 20, pp.100685. ⟨10.1016/j.nme.2019.100685⟩. ⟨hal-02468035⟩
G. Farag, Pierre Boivin, P. Sagaut. Interaction of two-dimensional spots with a heat releasing/absorbing shock wave: linear interaction approximation results. Journal of Fluid Mechanics, 2019, 871, pp.865-895. ⟨10.1017/jfm.2019.324⟩. ⟨hal-02142649⟩ Plus de détails...
The canonical interaction between a two-dimensional weak Gaussian disturbance (en-tropy spot, density spot, weak vortex) with an exothermic/endothermic planar shock wave is studied via the Linear Interaction Approximation. To this end, a unified framework based on an extended Kovasznay decomposition that simultaneously accounts for non-acoustic density disturbances along with a poloidal-toroidal splitting of the vorticity mode and for heat-release is proposed. An extended version of Chu's definition for the energy of disturbances in compressible flows encompassing multi-component mixtures of gases is also proposed. This new definition precludes spurious non-normal phenomena when computing the total energy of extended Kovasznay modes. Detailed results are provided for three cases, along with fully general expressions for mixed solutions that combine incoming vortical, entropy and density disturbances.
G. Farag, Pierre Boivin, P. Sagaut. Interaction of two-dimensional spots with a heat releasing/absorbing shock wave: linear interaction approximation results. Journal of Fluid Mechanics, 2019, 871, pp.865-895. ⟨10.1017/jfm.2019.324⟩. ⟨hal-02142649⟩
R Mao, N. Fedorczak, G. Ciraolo, H. Bufferand, Y. Marandet, et al.. Impact of alternative divertor configuration on plasma detachment: pure Deuterium simulations with SolEdge2D-EIRENE edge transport code for HL-2M scenario. Nuclear Fusion, 2019. ⟨hal-02370418⟩ Plus de détails...
The SOLEDGE-EIRENE edge plasma code provides solutions for particle & energy transport in the plasma edge within complex and realistic 2D geometries [1]. In this work, divertor detachment is simulated on the HL-2M alternative magnetic configurations in pure Deuterium plasma. Starting from typical HL-2M low single-null (SN) configuration, the snowflake plus (SF+) and snowflake minus (SF-) configurations have been investigated. Detachment of the outer target is studied in these configurations during plasma density ramps controlled by a fueling source, at constant input power and constant radial transport coefficients. Some typical characteristics of detachment, like threshold, depth and upstream window of detachment are investigated. In the three geometries, detachment onset and evolution with upstream plasma density is characterized by the gradual displacement of a radiation front from the outer target to the main X-point, as observed in experiments. It is found that, whatever the detachment in terms of particle, momentum or power dissipation, the detachment threshold is dominated primarily by the geometrical structure of divertor plate and it does not exhibit dependence on the magnetic configuration of the diverted plasma volume. In particular, the parallel connection length in the divertor is not found to affect the detachment threshold, in contrast with simple expectations from the 2-point model, but in agreement with experimental findings.
R Mao, N. Fedorczak, G. Ciraolo, H. Bufferand, Y. Marandet, et al.. Impact of alternative divertor configuration on plasma detachment: pure Deuterium simulations with SolEdge2D-EIRENE edge transport code for HL-2M scenario. Nuclear Fusion, 2019. ⟨hal-02370418⟩
Isabelle Cheylan, Guillaume Fritz, Denis Ricot, Pierre Sagaut. Shape Optimization Using the Adjoint Lattice Boltzmann Method for Aerodynamic Applications. AIAA Journal, 2019, 57 (7), pp.2758-2773. ⟨10.2514/1.J057955⟩. ⟨hal-02468051⟩ Plus de détails...
The present work focuses on shape optimization using the lattice Boltzmann method applied to aerodynamic cases. The adjoint method is used to calculate the sensitivities of the drag force with respect to the shape of an object. The main advantage of the adjoint method is its cost, because it is independent from the number of optimization parameters. The approach used consists in developing a continuous adjoint of the primal problem discretized in space, time, and velocities. An adjoint lattice Boltzmann equation is thus found, which is solved using the same algorithms as in the primal problem. The test cases investigate new features compared to what exists in the literature, such as the derivation of the grid refinement models in the primal problem to obtain their adjoint counterparts, but also the derivation of a double-relaxation-time algorithm and the Ginzburg et al. interpolation at the wall ("Two-Relaxation-Time Lattice Boltzmann Scheme: About Parametrization, Velocity, Pressure and Mixed Boundary Conditions," Communications in Computational Physics, Vol. 3, No. 2, 2008, pp. 427-478). Regarding the unsteadiness of the primal problem, two methods differing in accuracy and computational effort are compared using a two-dimensional unsteady case. Finally, this first-of-a-kind adjoint solver is applied to a large-scale threedimensional turbulent case (the flow of air around a car at a speed of 130 km/h), which shows its usefulness in the industry.
Isabelle Cheylan, Guillaume Fritz, Denis Ricot, Pierre Sagaut. Shape Optimization Using the Adjoint Lattice Boltzmann Method for Aerodynamic Applications. AIAA Journal, 2019, 57 (7), pp.2758-2773. ⟨10.2514/1.J057955⟩. ⟨hal-02468051⟩
Lars Davidson, Christophe Friess. A new formulation of f k for the PANS model. Journal of Turbulence, 2019, 20 (5), pp.322-336. ⟨10.1080/14685248.2019.1641605⟩. ⟨hal-02354566⟩ Plus de détails...
Lars Davidson, Christophe Friess. A new formulation of f k for the PANS model. Journal of Turbulence, 2019, 20 (5), pp.322-336. ⟨10.1080/14685248.2019.1641605⟩. ⟨hal-02354566⟩
E. Yim, P. Meliga, F. Gallaire. Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019, 475 (2225), pp.20190018. ⟨10.1098/rspa.2019.0018⟩. ⟨hal-02177032⟩ Plus de détails...
We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent-incoherent interaction is lumped into a Reynolds averaged Navier-Stokes (RANS) eddy viscosity model, and the mean-coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantic-Lugo & Gallaire (2016 J. Fluid Mech. 793, 777-797. (doi:10.1017/jfm.2016.109)). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.
E. Yim, P. Meliga, F. Gallaire. Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019, 475 (2225), pp.20190018. ⟨10.1098/rspa.2019.0018⟩. ⟨hal-02177032⟩
Journal: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, Eric Serre, P. Tamain. A magnetic-field independent approach for strongly anisotropic equations arising plasma-edge transport simulations. Nuclear Materials and Energy, 2019, 19, pp.340-345. ⟨10.1016/j.nme.2019.03.002⟩. ⟨hal-02177048⟩ Plus de détails...
A [Summary] The control of the power exhaust in tokamaks is still an open issue for the future fusion operations. The heat loads on divertor and limiter PFCs is largely determined by the physics of the Scrape-Off Layer (SOL), and therefore it depends mainly on the geometry of the magnetic surfaces and on the geometry of wall components. A better characterization of the heat exhaust mechanisms requires therefore to improve the capabilities of the transport codes in terms of geometrical description of the wall components and in terms of the description of the magnetic geometry. The possibility of dealing with evolving magnetic configurations becomes also critical: during start-up or control operations, for example, the evolution of particles and heat fluxes is little known, although being critical for the safety of the machine. Hence, among the new capabilities of future transport codes will be the possibility of accurately describe the reactor chamber, and the flexibility with respect the magnetic configuration. In particular, avoiding expensive re-meshing of the computational domain in case of evolving equilibrium is mandatory. In order to fulfill these requirements, in this work a fluid solver based on non-aligned discretization is used to solve the plasma-edge transport equations for density, momentum and energies. Preliminary tests on non-structured meshes and realistic geometries/physical parameters show the pertinency of this novel approach.
Giorgio Giorgiani, H. Bufferand, G. Ciraolo, Eric Serre, P. Tamain. A magnetic-field independent approach for strongly anisotropic equations arising plasma-edge transport simulations. Nuclear Materials and Energy, 2019, 19, pp.340-345. ⟨10.1016/j.nme.2019.03.002⟩. ⟨hal-02177048⟩
S. Baschetti, H. Bufferand, G. Ciraolo, N. Fedorczak, P. Ghendrih, et al.. A κ − ε model for plasma anomalous transport in tokamaks: closure via the scaling of the global confinement. Nuclear Materials and Energy, 2019, 19, pp.200-204. ⟨10.1016/j.nme.2019.02.032⟩. ⟨hal-02177039⟩ Plus de détails...
A reduced model for radial anomalous transport of plasma in tokamaks, inspired by the Reynolds-Averaged Navier-Stokes (RANS) approach, is presented assuming diffusion as governing mechanism. In order to self-consistently calculate transport coefficients, an empirical equation is built for the turbulent kinetic energy and the system is closed via the scaling law of global confinement. In such way the SOL width appears to recover experimental dependencies with respect to machine parameters and interestingly, when the model is implemented in a 2D transport code for a realistic study-case, mean fields retrieve some features already observed in 1st-principle turbulent codes.
S. Baschetti, H. Bufferand, G. Ciraolo, N. Fedorczak, P. Ghendrih, et al.. A κ − ε model for plasma anomalous transport in tokamaks: closure via the scaling of the global confinement. Nuclear Materials and Energy, 2019, 19, pp.200-204. ⟨10.1016/j.nme.2019.02.032⟩. ⟨hal-02177039⟩
Uwe Ehrenstein. Thrust and drag scaling of a rigid low-aspect-ratio pitching plate. Journal of Fluids and Structures, 2019, 87, pp.39-57. ⟨10.1016/j.jfluidstructs.2019.03.013⟩. ⟨hal-02090856⟩ Plus de détails...
Uwe Ehrenstein. Thrust and drag scaling of a rigid low-aspect-ratio pitching plate. Journal of Fluids and Structures, 2019, 87, pp.39-57. ⟨10.1016/j.jfluidstructs.2019.03.013⟩. ⟨hal-02090856⟩
Pierre Magnico. Electro-Kinetic Instability in a Laminar Boundary Layer Next to an Ion Exchange Membrane. International Journal of Molecular Sciences, 2019, 20 (10), pp.2393. ⟨10.3390/ijms20102393⟩. ⟨hal-02177052⟩ Plus de détails...
The electro-kinetic instability in a pressure driven shear flow near an ion exchange membrane is considered. The electrochemical system, through which an electrical potential drop is applied, consists in a polarization layer in contact with the membrane and a bulk. The numerical investigation contained two aspects: analysis of the instability modes and description of the Lagrangian transport of fluid and ions. Regarding the first aspect, the modes were analyzed as a function of the potential drop. The analysis revealed how the spatial distribution of forces controls the dynamics of vortex association and dissociation. In particular, the birth of a counter-clockwise vortex between two clockwise vortices, and the initiation of clusters constituting one or two envelopes wrapping a vortex group, were examined. In regards to the second aspect, the trajectories were computed with the fourth order Runge Kutta scheme for the time integration and with the biquadratric upstream scheme for the spatial and time interpolation of the fluid velocity and the ion flux. The results for the periodic mode showed two kinds of trajectories: the trochoidal motion and the longitudinal one coupled with a periodic transverse motion. For the aperiodic modes, other mechanisms appeared, such as ejection from the mixing layer, trapping by a growing vortex or merging vortices. The analysis of the local velocity field, the vortices' shape, the spatial distribution of the forces and the ion flux components explained these trajectories.
Pierre Magnico. Electro-Kinetic Instability in a Laminar Boundary Layer Next to an Ion Exchange Membrane. International Journal of Molecular Sciences, 2019, 20 (10), pp.2393. ⟨10.3390/ijms20102393⟩. ⟨hal-02177052⟩
Journal: International Journal of Molecular Sciences
Julien Denis, J. Bucalossi, G. Ciraolo, Etienne A Hodille, B. Pégourié, et al.. Dynamic modelling of local fuel inventory and desorption in the whole tokamak vacuum vessel for auto-consistent plasma-wall interaction simulations. Nuclear Materials and Energy, 2019, 19, pp.550-557. ⟨10.1016/j.nme.2019.03.019⟩. ⟨hal-02902060⟩ Plus de détails...
An extension of the SolEdge2D-EIRENE code package, named D-WEE, has been developed to add the dynamics of thermal desorption of hydrogen isotopes from the surface of plasma facing materials. To achieve this purpose, D-WEE models hydrogen isotopes implantation, transport and retention in those materials. Before launching auto-consistent simulation (with feedback of D-WEE on SolEdge2D-EIRENE), D-WEE has to be initialised to ensure a realistic wall behaviour in terms of dynamics (pumping or fuelling areas) and fuel content. A methodology based on modelling is introduced to perform such initialisation. A synthetic plasma pulse is built from consecutive SolEdge2D-EIRENE simulations. This synthetic pulse is used as a plasma background for the D-WEE module. A sequence of plasma pulses is simulated with D-WEE to model a tokamak operation. This simulation enables to extract at a desired time during a pulse the local fuel inventory and the local desorption flux density which could be used as initial condition for coupled plasma-wall simulations. To assess the relevance of the dynamic retention behaviour obtained in the simulation, a confrontation to post-pulse experimental pressure measurement is performed. Such confrontation reveals a qualitative agreement between the temporal pressure drop obtained in the simulation and the one observed experimentally. The simulated dynamic retention during the consecutive pulses is also studied.
Julien Denis, J. Bucalossi, G. Ciraolo, Etienne A Hodille, B. Pégourié, et al.. Dynamic modelling of local fuel inventory and desorption in the whole tokamak vacuum vessel for auto-consistent plasma-wall interaction simulations. Nuclear Materials and Energy, 2019, 19, pp.550-557. ⟨10.1016/j.nme.2019.03.019⟩. ⟨hal-02902060⟩
V.S. Neverov, A.B. Kukushkin, U. Kruezi, M.F. Stamp, H. Weisen, et al.. Determination of isotope ratio in the divertor of JET-ILW by high-resolution H α spectroscopy: H–D experiment and implications for D–T experiment. Nuclear Fusion, 2019, 59 (4), pp.046011. ⟨10.1088/1741-4326/ab0000⟩. ⟨hal-02177120⟩ Plus de détails...
The data of the H alpha high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertor is found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertor than that in the outer divertor by the values of 0.15-0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertor in the upcoming deuterium-tritium experiments. Also, separation of the overlapped T alpha and D alpha spectral lines is shown to be a challenging task especially when the local Doppler-broadened (Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium-tritium experiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic's measurements. This model is shown to increase the accuracy of tritium concentration measurements in the divertor.
V.S. Neverov, A.B. Kukushkin, U. Kruezi, M.F. Stamp, H. Weisen, et al.. Determination of isotope ratio in the divertor of JET-ILW by high-resolution H α spectroscopy: H–D experiment and implications for D–T experiment. Nuclear Fusion, 2019, 59 (4), pp.046011. ⟨10.1088/1741-4326/ab0000⟩. ⟨hal-02177120⟩
P. Ström, P. Petersson, M. Rubel, E. Fortuna-Zaleśna, A. Widdowson, et al.. Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, 2019, 516, pp.202-213. ⟨10.1016/j.jnucmat.2018.11.027⟩. ⟨hal-02177126⟩ Plus de détails...
Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analysed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 mu m were indicated, but typical values were on the order of a few hundred nm. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 mu m were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.
P. Ström, P. Petersson, M. Rubel, E. Fortuna-Zaleśna, A. Widdowson, et al.. Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall. Journal of Nuclear Materials, 2019, 516, pp.202-213. ⟨10.1016/j.jnucmat.2018.11.027⟩. ⟨hal-02177126⟩
Marco Martins Afonso, Philippe Meliga, Eric Serre. Optimal Transient Growth in an Incompressible Flow past a Backward-Slanted Step. Fluids, 2019, 4 (1), pp.33. ⟨10.3390/fluids4010033⟩. ⟨hal-02176963⟩ Plus de détails...
With the aim of providing a first step in the quest for a reduction of the aerodynamic drag on the rear-end of a car, we study the phenomena of separation and reattachment of an incompressible flow by focusing on a specific aerodynamic geometry, namely a backward-slanted step at 25 circle of inclination. The ensuing recirculation bubble provides the basis for an analytical and numerical investigation of streamwise-streak generation, lift-up effect, and turbulent-wake and Kelvin-Helmholtz instabilities. A linear stability analysis is performed, and an optimal control problem with a steady volumic forcing is tackled by means of a variational formulation, adjoint methods, penalization schemes, and an orthogonalization algorithm. Dealing with the transient growth of spanwise-periodic perturbations, and inspired by the need of physically-realizable disturbances, we finally provide a procedure attaining a kinetic-energy maximal gain on the order of 106, with respect to the power introduced by the external forcing.
Marco Martins Afonso, Philippe Meliga, Eric Serre. Optimal Transient Growth in an Incompressible Flow past a Backward-Slanted Step. Fluids, 2019, 4 (1), pp.33. ⟨10.3390/fluids4010033⟩. ⟨hal-02176963⟩
Gauthier Wissocq, Pierre Sagaut, Jean-François Boussuge. An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues. Journal of Computational Physics, 2019, 380, pp.311-333. ⟨10.1016/j.jcp.2018.12.015⟩. ⟨hal-02176969⟩ Plus de détails...
An extension of the von Neumann linear analysis is proposed for the study of the discrete-velocity Boltzmann equation (DVBE) and the lattice Boltzmann (LB) scheme. While the standard technique is restricted to the investigation of the spectral radius and the dissipation and dispersion properties, a new focus is put here on the information carried by the modes. The technique consists in the computation of the moments of the eigenvectors and their projection onto the physical waves expected by the continuous linearized Navier-Stokes (NS) equations. The method is illustrated thanks to some simulations with the BGK (Bhatnagar-Gross-Krook) collision operator on the D2Q9 and D2V17 lattices. The present analysis reveals the existence of two kinds of modes: non-observable modes that do not carry any macroscopic information and observable modes. The latter may carry either a physical wave expected by the NS equations, or an unphysical information. Further investigation of modal interactions highlights a phenomenon called curve veering occurring between two observable modes: a swap of eigenvectors and dissipation rate is observed between the eigencurves. Increasing the Mach number of the mean flow yields an eigenvalue collision at the origin of numerical instabilities of the BGK model, arising from the error in the time and space discretization of the DVBE. (C) 2019 Elsevier Inc. All rights reserved.
Gauthier Wissocq, Pierre Sagaut, Jean-François Boussuge. An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues. Journal of Computational Physics, 2019, 380, pp.311-333. ⟨10.1016/j.jcp.2018.12.015⟩. ⟨hal-02176969⟩
Davide Galassi, Guido Ciraolo, Patrick Tamain, Hugo Bufferand, Philippe Ghendrih, et al.. Tokamak edge plasma turbulence interaction with magnetic X-point in 3D global simulations. Fluids, 2019, 4 (1), pp.50. ⟨10.3390/fluids4010050⟩. ⟨hal-02176982⟩ Plus de détails...
Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.
Davide Galassi, Guido Ciraolo, Patrick Tamain, Hugo Bufferand, Philippe Ghendrih, et al.. Tokamak edge plasma turbulence interaction with magnetic X-point in 3D global simulations. Fluids, 2019, 4 (1), pp.50. ⟨10.3390/fluids4010050⟩. ⟨hal-02176982⟩
K. Lawson, K Aggarwal, I. Coffey, K Keenan, M O’mullane, et al.. Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model. Journal of Physics B: Atomic, Molecular and Optical Physics, 2019, 52 (4), pp.045001. ⟨10.1088/1361-6455/aaf703⟩. ⟨hal-02177115⟩ Plus de détails...
Helium is widely used as a fuel or minority gas in laboratory fusion experiments, and will be present as ash in DT thermonuclear plasmas. It is therefore essential to have a good understanding of its atomic physics. To this end He II population modelling has been undertaken for the spectroscopic levels arising from shells with principal quantum number n = 1-5. This paper focuses on a collisional excitation model; ionisation and recombination will be considered in a subsequent article. Heavy particle collisional excitation rate coefficients have been generated to supplement the currently-available atomic data for He II, and are presented for proton, deuteron, triton and alpha-particle projectiles. The widely-used criterion for levels within an n shell being populated in proportion to their statistical weights is reassessed with the most recent atomic data, and found not to apply to the He II levels at tokamak densities (10(18)-10(21) m(-3)). Consequences of this and other likely sources of errors are quantified, as is the effect of differing electron and ion temperatures. Line intensity ratios, including the so-called 'branching ratios' and the fine-structure beta(1), beta(2), beta(3), and gamma ratios, are discussed, the latter with regard to their possible use as diagnostics.
K. Lawson, K Aggarwal, I. Coffey, K Keenan, M O’mullane, et al.. Population modelling of the He II energy levels in tokamak plasmas: I. Collisional excitation model. Journal of Physics B: Atomic, Molecular and Optical Physics, 2019, 52 (4), pp.045001. ⟨10.1088/1361-6455/aaf703⟩. ⟨hal-02177115⟩
Journal: Journal of Physics B: Atomic, Molecular and Optical Physics
Mohamad Cheayb, Mylène Marin Gallego, Mohand Tazerout, Sébastien Poncet. Modelling and experimental validation of a small-scale trigenerative compressed air energy storage system. Applied Energy, 2019, 239, pp.1371-1384. ⟨10.1016/j.apenergy.2019.01.222⟩. ⟨hal-02384256⟩ Plus de détails...
• A thermodynamic model of a simple trigenerative-CAES is developed. • The model is validated experimentally. • The performances of the simple configuration are assessed. • Technological issues on the trigenerative CAES are highlighted. New advances in compressed air energy storage systems have been recently made especially regarding the use of heat generated from compression. On this basis, the concept of the trigenerative compressed air energy storage (T-CAES) has recently been proposed. Many studies highlighted the feasibility and the benefits of this system to be placed close to the energy demand. The aim of this study is to examine a simple configuration of this system by a coupled experimental/mod-elling approach. This paper presents a detailed thermodynamic model of both the main components and the whole system. An experimental bench is used to validate the model and to investigate the effect of the operating parameters on the system efficiency and the model accuracy. The model predictions are consistent with the experimental measurements during the charge, storage and discharge phases. It has been found that the temperature drop across the pressure regulator should not be ignored and is governed by the Joule-Thomson effect. Besides, it has been observed that the input temperature of the air motor must be accounted for in the assessment of future improved configurations. It was noted that the system efficiency increases significantly by adding the cooling and heating potentials. However, the round trip efficiency remains low at 15.6%. Output values of the model are in good agreement with the experimental results with an error less than 13.2%. The model can be applied as a basis for the performance assessment of prospective configurations and improvements of trigenerative compressed air energy storage.
Mohamad Cheayb, Mylène Marin Gallego, Mohand Tazerout, Sébastien Poncet. Modelling and experimental validation of a small-scale trigenerative compressed air energy storage system. Applied Energy, 2019, 239, pp.1371-1384. ⟨10.1016/j.apenergy.2019.01.222⟩. ⟨hal-02384256⟩
T. Vasilopoulou, I.E. Stamatelatos, P. Batistoni, A. Colangeli, D. Flammini, et al.. Improved neutron activation dosimetry for fusion. Fusion Engineering and Design, 2019, 139, pp.109-114. ⟨10.1016/j.fusengdes.2019.01.002⟩. ⟨hal-02177100⟩ Plus de détails...
Neutron activation technique has been widely used for the monitoring of neutron fluence at the Joint European Torus (JET) whereas it is foreseen to be employed at future fusion plants, such as ITER and DEMO. Neutron activation provides a robust tool for the measurement of neutron fluence in the complex environment encountered in a tokamak. However, activation experiments previously performed at JET showed that the activation foils used need to be calibrated in a real fusion environment in order to provide accurate neutron fluence data. Triggered by this challenge, an improved neutron activation method for the evaluation of neutron fluence at fusion devices has been developed. Activation assemblies similar to those used at JET were irradiated under 14 MeV neutrons at the Frascati Neutron Generator (FNG) reference neutron field. The data obtained from the calibration experiment were applied for the analysis of activation foil measurements performed during the implemented JET Deuterium-Deuterium (D-D) campaign. The activation results were compared against thermoluminescence measurements and a satisfactory agreement was observed. The proposed method provides confidence on the use of activation technique for the precise estimation of neutron fluence at fusion devices and enables its successful implementation in the forthcoming JET Deuterium-Tritium (D-T) campaign.
T. Vasilopoulou, I.E. Stamatelatos, P. Batistoni, A. Colangeli, D. Flammini, et al.. Improved neutron activation dosimetry for fusion. Fusion Engineering and Design, 2019, 139, pp.109-114. ⟨10.1016/j.fusengdes.2019.01.002⟩. ⟨hal-02177100⟩
A. Drenik, S. Brezinsek, P. Carvalho, V. Huber, N. Osterman, et al.. Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET. Fusion Engineering and Design, 2019, 139, pp.115-123. ⟨10.1016/j.fusengdes.2018.12.079⟩. ⟨hal-02177109⟩ Plus de détails...
Hot spots on the divertor tiles at JET result in overestimation of the tile surface temperature which causes unnecessary termination of pulses. However, the appearance of hot spots can also indicate the condition of the divertor tile surfaces. To analyse the behaviour of the hot spots in the outer divertor tiles of JET, a simple image processing algorithm is developed. The algorithm isolates areas of bright pixels in the camera image and compares them to previously identified hot spots. The activity of the hot spots is then linked to values of other signals and parameters in the same time intervals. The operation of the detection algorithm was studied in a limited pulse range with high hot spot activity on the divertor tiles 5, 6 and 7. This allowed us to optimise the values of the controlling parameters. Then, the wider applicability of the method has been demonstrated by the analysis of the hot spot behaviour in a whole experimental campaign.
A. Drenik, S. Brezinsek, P. Carvalho, V. Huber, N. Osterman, et al.. Analysis of the outer divertor hot spot activity in the protection video camera recordings at JET. Fusion Engineering and Design, 2019, 139, pp.115-123. ⟨10.1016/j.fusengdes.2018.12.079⟩. ⟨hal-02177109⟩
F. Muller, A. Burbeau, B.-J. Gréa, Pierre Sagaut. Minimum enstrophy principle for two-dimensional inviscid flows around obstacles. Physical Review E , 2019, 99 (2), ⟨10.1103/PhysRevE.99.023105⟩. ⟨hal-02176949⟩ Plus de détails...
Large-scale coherent structures emerging in two-dimensional flows can be predicted from statistical physics inspired methods consisting in minimizing the global enstrophy while conserving the total energy and circulation in the Euler equations. In many situations, solid obstacles inside the domain may also constrain the flow and have to be accounted for via a minimum enstrophy principle. In this work, we detail this extended variational formulation and its numerical resolution. It is shown from applications to complex geometries containing multiple circular obstacles that the number of solutions is enhanced, allowing many possibilities of bifurcations for the large-scale structures. These phase change phenomena can explain the downstream recombinations of the flow in rod-bundle experiments and simulations.
F. Muller, A. Burbeau, B.-J. Gréa, Pierre Sagaut. Minimum enstrophy principle for two-dimensional inviscid flows around obstacles. Physical Review E , 2019, 99 (2), ⟨10.1103/PhysRevE.99.023105⟩. ⟨hal-02176949⟩
Elena Alekseenko, Bernard Roux. Contribution to remediation of brackish lagoon: 3D simulation of salinity, bottom currents and resuspension of bottom sediments by strong winds. Estuarine, Coastal and Shelf Science, 2019, 216, pp.27-37. ⟨10.1016/j.ecss.2018.05.021⟩. ⟨hal-01813824⟩ Plus de détails...
This work concerns the modelling and numerical simulation of the 3D salinity and current distribution in a very shallow Mediterranean lagoon subject to strong winds which create intensive resuspension of polluted bottom sediments. We consider wind speeds of 10 m/s and 20 m/s in the two dominant wind directions (N-NW and S-SE). This study is made for different scenarios of flow exchanges with the surrounding hydrosystems: a brackish lagoon on the North (the Etang de Berre), the Cadiere River on the East, and a brackish channel on the South (the Rove channel). The bottom shear stress (BSS) are compared to the BBS threshold given in the literature in terms of the bottom roughness. It permits to determine which kind of bottom sediments (muds and sands) will be resuspended by each wind. The bottom currents permit to predict in which direction the suspended sediments will be moved and where are the sedimentary deposit zones. It provides a guide for the specialists of remediation of the lagoon for a mechanical extraction of sediments in such zones. In addition, numerical experiments have been performed to understand how the salinity distribution depends on the flow exchanges with the two brackish surrounding hydrosystems. This new knowledge will permit the owner of this lagoon to know how to maintain efficiently the level of salinity in the suitable range.
Elena Alekseenko, Bernard Roux. Contribution to remediation of brackish lagoon: 3D simulation of salinity, bottom currents and resuspension of bottom sediments by strong winds. Estuarine, Coastal and Shelf Science, 2019, 216, pp.27-37. ⟨10.1016/j.ecss.2018.05.021⟩. ⟨hal-01813824⟩
Elena Alekseenko, Bernard Roux. Wind effect on bottom shear stress, erosion and redeposition on Zostera noltei restoration in a coastal lagoon; Part 2. Estuarine, Coastal and Shelf Science, 2019, 216, pp.14-26. ⟨10.1016/j.ecss.2018.05.022⟩. ⟨hal-01813834⟩ Plus de détails...
This paper concerns wind effect on bottom shear stress (BSS), resuspension and redeposition of bottom sediments in the nearshore areas of the Etang de Berre (EB), a semi-enclosed lagoon, in the context of Zostera noltei (Z.n.) restoration. As in our previous paper, the first step is to compare BSS with its threshold, BSScr, for a wind speed of 21 m/s. But, here, a new simulation is performed for 16 wind directions regularly spaced. It permits to analyze the combined effect, over one year, of these winds on the erosion risk. For that, a mean value of |BSS|, i.e., a weighted average based on the frequency of each wind directions, has been determined and compared to for a class of roughness parameters. A similar averaging of BSS has been also evaluated to obtain the direction of an average bottom current. Then, the most important contribution of the present paper concerns the modelling of the wind-induced sediment erosion, transport and redeposition. The specific module SEDIM/MARS3D is used to determine how the thickness of a given mud-sand sedimentary layer can be changed by the wind-induced current during typical periods of 3 days of constant wind. This numerical study is performed for three wind speeds in the two main wind directions: N-NW and S-SE. The time evolution of this initial sedimentary layer permits to determine where and when the erosion would be large enough to be a stressor for the Z.n. restoration. For an extreme erosion rate of 10-3kg/m2/s, for a strong wind speed of 21 m/s and an initial sedimentary layer of 15 cm, all this layer would be eroded in several nearshore areas after 3 days. The erosion risk is maximum along the eastern shore, where an additive effect of the two opposite winds can be expected. Indeed, S-SE and N-NW winds create coastal jets of opposite direction and of about the same intensity exerting alongshore erosion and deposition at about the same places. The present results concerning the time evolution of erosion depth induced by the wind improve our knowledge of the erosion risk on the Z.n. restoration in EB. They will be useful to appropriately orient the action of politics and managers for a future restoration program.
Elena Alekseenko, Bernard Roux. Wind effect on bottom shear stress, erosion and redeposition on Zostera noltei restoration in a coastal lagoon; Part 2. Estuarine, Coastal and Shelf Science, 2019, 216, pp.14-26. ⟨10.1016/j.ecss.2018.05.022⟩. ⟨hal-01813834⟩
Shahram Khazaie, Xun Wang, Dimitri Komatitsch, Pierre Sagaut. Uncertainty quantification for acoustic wave propagation in a shallow water environment. Wave Motion, 2019, 91, pp.102390. ⟨10.1016/j.wavemoti.2019.102390⟩. ⟨hal-02467993⟩ Plus de détails...
Sound wave propagation in a shallow water environment is complex due to e.g. the uncertainties of sound speed profile being inhomogeneous and imprecisely measured, the bottom reflections, etc. The propagation and influence of several uncertainty parameters are quantified in this paper. A four-layer model, which can approximately represent a wide range of shallow water environments, is considered; six parameters representing sound speed profile and water depth are considered as random variables. We investigate how the wave field (pressure) in this model is influenced by these uncertainties. For this purpose, the sound field is computed for different realizations of the random variables, when the medium is excited with sources whose frequencies are appropriate, for example, for marine seismic exploration applications. Since classical Monte Carlo methods require a huge sample size to converge, we use three surrogate modeling techniques (Kriging, Polynomial Chaos, and Polynomial Chaos-based Kriging). The proposed methods require much smaller sample sizes, which makes the uncertainty quantification (UQ) possible. Wavelength-to-depth ratio (lambda/d) is introduced as the key parameter that defines the degree of interaction (reflection and transmission) of the sound waves with the boundaries of the shallow water waveguide. The results show that for small and large values of lambda/d, the wave field is more sensitive to the variations of the water depth and the velocity of the bottom layer, respectively. The robustness (precision) of the surrogate models is shown to decrease for lower values of lambda/d. The proposed UQ methodology can be used for more complicated underwater environments; it is even more advantageous because it can efficiently deal with a large number of model uncertainty parameters and identify the most influential ones.
Shahram Khazaie, Xun Wang, Dimitri Komatitsch, Pierre Sagaut. Uncertainty quantification for acoustic wave propagation in a shallow water environment. Wave Motion, 2019, 91, pp.102390. ⟨10.1016/j.wavemoti.2019.102390⟩. ⟨hal-02467993⟩
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized thermal lattice Boltzmann model for high subsonic compressible flows. Journal of Computational Physics, 2019, 394, pp.82-99. ⟨hal-02142837⟩ Plus de détails...
A thermal lattice Boltzmann model with a hybrid recursive regularization (HRR) collision operator is developed on standard lattices for simulation of subsonic and sonic compressible flows without shock. The approach is hybrid: mass and momentum conservation equations are solved using a lattice Boltzmann solver, while the energy conservation is solved under entropy form with a finite volume solver. The defect of Galilean invariance related to Mach number is corrected by the third order equilibrium distribution function , supplemented by an additional correcting term and hybrid recursive regularization. The proposed approach is assessed considering the simulation of i) an isentropic vortex convection, ii) a two dimensional acoustic pulse and iii) non-isothermal Gaussian pulse with Ma number in range of 0 to 1. Numerical simulations demonstrate that the flaw in Galilean invari-ance is effectively eliminated by the compressible HRR model. At last, the compressible laminar flows over flat plate at Ma number of 0.3 and 0.87, Reynolds number of 10 5 are considered to validate the capture of viscous and diffusive effects.
Yongliang Feng, Pierre Boivin, Jérome Jacob, Pierre Sagaut. Hybrid recursive regularized thermal lattice Boltzmann model for high subsonic compressible flows. Journal of Computational Physics, 2019, 394, pp.82-99. ⟨hal-02142837⟩
H. Bufferand, P. Tamain, S. Baschetti, J. Bucalossi, G. Ciraolo, et al.. Three-dimensional modelling of edge multi-component plasma taking into account realistic wall geometry. Nuclear Materials and Energy, 2019, 18, pp.82-86. ⟨10.1016/j.nme.2018.11.025⟩. ⟨hal-02176521⟩ Plus de détails...
H. Bufferand, P. Tamain, S. Baschetti, J. Bucalossi, G. Ciraolo, et al.. Three-dimensional modelling of edge multi-component plasma taking into account realistic wall geometry. Nuclear Materials and Energy, 2019, 18, pp.82-86. ⟨10.1016/j.nme.2018.11.025⟩. ⟨hal-02176521⟩
F. Nespoli, H. Bufferand, M. Valentinuzzi, N. Fedorczak, G. Ciraolo, et al.. Application of a two-fluid two-point model to SolEdge2D-EIRENE simulations of TCV H-mode plasma. Nuclear Materials and Energy, 2019, 18, pp.29-34. ⟨10.1016/j.nme.2018.11.026⟩. ⟨hal-02176505⟩ Plus de détails...
The edge and scrape-off layer (SOL) plasma of the inter-ELM phase of an H-mode discharge from the TCV tokamak is modeled with the transport code SolEdge2D-EIRENE (Bufferand et al. Nuclear Fusion 55 (2015)). The numerical simulations, in presence and in absence of C impurities sputtered from the first wall, are presented and compared with the experiments, finding an overall good agreement. The application of the standard two-point model to the simulation results leads to an apparent momentum gain along the divertor leg. A two-fluid two-point model featuring thermally decoupled ions and electrons is introduced and applied to the simulation results, overcoming this apparent discrepancy.
F. Nespoli, H. Bufferand, M. Valentinuzzi, N. Fedorczak, G. Ciraolo, et al.. Application of a two-fluid two-point model to SolEdge2D-EIRENE simulations of TCV H-mode plasma. Nuclear Materials and Energy, 2019, 18, pp.29-34. ⟨10.1016/j.nme.2018.11.026⟩. ⟨hal-02176505⟩
J. Soler, F. Schwander, G Giorgiani, J Liandrat, P Tamain, et al.. A new conservative finite-difference scheme for anisotropic elliptic problems in bounded domain A new conservative finite-difference scheme for anisotropic elliptic problems in bounded domain. Journal of Computational Physics, 2019, ⟨10.1016/j.jcp.2019.109093⟩. ⟨hal-02477007⟩ Plus de détails...
Highly anisotropic elliptic problems occur in many physical models that need to be solved numerically. A direction of dominant diffusion is thus introduced (called here parallel direction) along which the diffusion coefficient is several orders larger of magnitude than in the perpendicular one. In this case, finite-difference methods based on misaligned stencils are generally not designed to provide an optimal discretization, and may lead the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. This paper proposes an original scheme using non-aligned Cartesian grids and interpolations aligned along a parallel diffusion direction. Here, this direction is assumed to be supported by a divergence-free vector field which never vanishesand it is supposed to be stationary in time. Based on the Support Operator Method (SOM), the self-adjointness property of the parallel diffusion operator is maintained on the discrete level. Compared with existing methods, the present formulation further guarantees the conservativity of the fluxes in both parallel and perpendicular directions. In addition, when the flow intercepts a boundary in the parallel direction, an accurate discretization of the boundary condition is presented that avoids the uncertainties of extrapolated far ghost points classicaly used and ensures a better accuracy of the solution. Numerical tests based on manufactured solutions show the method is able to provide accurate and stable numerical approximations in both periodic and bounded domains with a drastically reduced number of degrees of freedom with respect to non-aligned approaches.
J. Soler, F. Schwander, G Giorgiani, J Liandrat, P Tamain, et al.. A new conservative finite-difference scheme for anisotropic elliptic problems in bounded domain A new conservative finite-difference scheme for anisotropic elliptic problems in bounded domain. Journal of Computational Physics, 2019, ⟨10.1016/j.jcp.2019.109093⟩. ⟨hal-02477007⟩
D.M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Effect of turbulent fluctuations on neutral particles transport with the TOKAM3X-EIRENE turbulence code. Nuclear Materials and Energy, 2019, 18, pp.105-110. ⟨10.1016/j.nme.2018.12.011⟩. ⟨hal-02176529⟩ Plus de détails...
The effect of turbulent fluctuations on the transport of neutral particles (atoms, molecules) in tokamak plasmas is investigated with the 3D global turbulence code TOKAM3X-EIRENE in limiter geometry. The statistical properties of turbulent fields relevant to this work are discussed, including the recycling flux. The neutral particle transport is recalculated on the mean field plasma, and compared to the mean neutral particle density/flows obtained from the turbulent simulation, so as to assess the effects of the fluctuations, in particular on the ionization balance. The latter effects are remarkably modest in the simulation presented here, but are expected to become more and more pronounced as the high recycling regime is approached, in particular because the plasma temperature becomes low enough so that ionization is strongly non-linear. However, the turbulent fluctuations in the SOL do have a substantial effect on the neutral densities on the low field side of the limiter, including in the confined plasma. These effects are traced back to non-linearities in the plasma flux at the wall, and the fluctuations in the latter are identified as an important contributor both to neutral particle density fluctuations and to deviations from mean neutral particle density/flows in the turbulent simulation with respect to the same quantities recalculated on the mean plasma fields.
D.M. Fan, Y. Marandet, P. Tamain, H. Bufferand, G. Ciraolo, et al.. Effect of turbulent fluctuations on neutral particles transport with the TOKAM3X-EIRENE turbulence code. Nuclear Materials and Energy, 2019, 18, pp.105-110. ⟨10.1016/j.nme.2018.12.011⟩. ⟨hal-02176529⟩
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, 2019, 148, pp.634-652. ⟨10.1016/j.buildenv.2018.11.009⟩. ⟨hal-02176936⟩ Plus de détails...
The goal of this study is to assess the performance of an innovative Lattice Boltzmann (LB) - Large Eddy Simulation (LES) approach in simulating neutral and stratified pollutant dispersion in complex urban environments. Different simulations are performed for the central area of Paris, accounting for continuous neutral or non-neutral gas releases from a circular source located in both channeled or confined flows. Predicted concentrations are compared with detailed wind tunnel measurements from the MODITIC project (FFI, 2016). Results exhibit a good qualitative and quantitative agreement between numerical and experimental data for the different configurations studied. All the estimated quality metrics match acceptance criteria. In addition, it is shown that the new LBM LES approach is able to capture and highlight the key turbulent mechanisms underlying dispersion process in and above urban areas. Hence, being based on extensive and detailed simulations and quality assurance studies, this paper highlights that the developed approach is well suited to address urban dispersion issues, including accidental chemical releases and short term exposure problems. Such results are particularly valuable to support the design and use of fast response dispersion models.
Lucie Merlier, Jérome Jacob, Pierre Sagaut. Lattice-Boltzmann large-eddy simulation of pollutant dispersion in complex urban environment with dense gas effect: Model evaluation and flow analysis. Building and Environment, 2019, 148, pp.634-652. ⟨10.1016/j.buildenv.2018.11.009⟩. ⟨hal-02176936⟩
Y. Hatano, S.E. Lee, J. Likonen, S. Koivuranta, M. Hara, et al.. Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign. Nuclear Materials and Energy, 2019, 18, pp.258-261. ⟨10.1016/j.nme.2019.01.001⟩. ⟨hal-02177095⟩ Plus de détails...
Tritium (T) distributions on tungsten (W)-coated plasma-facing tiles used in the third ITER-like wall campaign (2015-2016) of the Joint European Torus (JET) were examined by means of an imaging plate technique and beta-ray induced x-ray spectrometry, and they were compared with the distributions after the second (2013-2014) campaign. Strong enrichment of T in beryllium (Be) deposition layers was observed after the second campaign. In contrast, T distributions after the third campaign was more uniform though Be deposition layers were visually recognized. The one of the possible explanations is enhanced desorption of T from Be deposition layers due to higher tile temperatures caused by higher energy input in the third campaign.
Y. Hatano, S.E. Lee, J. Likonen, S. Koivuranta, M. Hara, et al.. Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign. Nuclear Materials and Energy, 2019, 18, pp.258-261. ⟨10.1016/j.nme.2019.01.001⟩. ⟨hal-02177095⟩
Philippe Meliga, Elie Hachem. Time-accurate calculation and bifurcation analysis of the incompressible flow over a square cavity using variational multiscale modeling. Journal of Computational Physics, 2019, 376, pp.952-972. ⟨10.1016/j.jcp.2018.09.036⟩. ⟨hal-01946893⟩ Plus de détails...
A thorough variational multiscale (VMS) modeling of the Navier-Stokes equations is used to compute numerical solutions of the incompressible flow over an open cavity. This case features several competing instabilities, and is highly challenging for VMS methods with regard to frequency and pattern selection, because of the non-normality of the linearized Navier-Stokes operator. The relevance of the approach is thus carefully assessed by comparing to direct numerical simulation (DNS) data benchmarked at several Reynolds numbers, and highly accurate time advancing methods are shown to predict relevant evolutions of the transient and saturated solutions. The VMS reduces substantially the computational cost, by similar to 35% (resp. similar to 60%) in terms of CPU time using a semi-implicit discretization scheme based on backward differentiation formula (resp. the implicit Crank-Nicholson scheme), and by similar to 80% in terms of memory requirement. Eventually, the highly efficient semi-implicit VMS numerical framework is used to unravel the onset of the flow oscillations and the selection of the limit cycle frequency, that happens to involve a subcritical Neimark-Sacker bifurcation.
Philippe Meliga, Elie Hachem. Time-accurate calculation and bifurcation analysis of the incompressible flow over a square cavity using variational multiscale modeling. Journal of Computational Physics, 2019, 376, pp.952-972. ⟨10.1016/j.jcp.2018.09.036⟩. ⟨hal-01946893⟩
G. Sias, B. Cannas, A. Fanni, A. Murari, A. Pau, et al.. A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion Engineering and Design, 2019, 138, pp.254-266. ⟨10.1016/j.fusengdes.2018.11.021⟩. ⟨hal-02177084⟩ Plus de détails...
The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different machines would facilitate the development of portable systems for disruption prediction, which is becoming of increasingly importance for the next tokamak generations. Moreover, the indicator allows us to overcome some intrinsic problems in the diagnostic system such as drift and offset. The behavior of the proposed indicator as disruption predictor, based on crossing optimized thresholds of the signal amplitude, has been analyzed using data of both JET and ASDEX Upgrade experiments. A thorough analysis of the disruption prediction performance shows how the indicator is able to recover some missed and tardy detections of the raw signal. Moreover, it intervenes and corrects premature or even wrong alarms due to, e.g., drifts and/or offsets.
G. Sias, B. Cannas, A. Fanni, A. Murari, A. Pau, et al.. A locked mode indicator for disruption prediction on JET and ASDEX upgrade. Fusion Engineering and Design, 2019, 138, pp.254-266. ⟨10.1016/j.fusengdes.2018.11.021⟩. ⟨hal-02177084⟩
Simon Gsell, Rémi Bourguet, Marianna Braza. One- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder at Re=3900. Journal of Fluids and Structures, 2019, 85, pp.165-180. ⟨10.1016/j.jfluidstructs.2019.01.006⟩. ⟨hal-02062155⟩ Plus de détails...
The one- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder are investigated on the basis of direct numerical simulation results. The Reynolds number, based on the oncoming flow velocity and cylinder diameter, is set to 3900. Three cases are examined: the elastically mounted body is free to oscillate either in the direction aligned with the current (in-line direction; IL case), in the direction normal to the current (cross-flow direction; CF case), or in both directions (IL+CF case). In each case, the behavior of the flow–structure system is studied over a range of values of the reduced velocity (inverse of the oscillator natural frequency). The in-line and cross-flow responses observed in the IL+CF case substantially differ from their one-degree-of-freedom counterparts, especially in the intermediate reduced velocity region. In this region, no vibrations develop in the IL case and in-line oscillations only occur if cross-flow motion is allowed. These in-line oscillations are accompanied by a major increase of the cross-flow responses, compared to the CF case. The two-degree-of-freedom vibrations are associated with the emergence of large-amplitude higher harmonics in the fluid force spectra. These aspects and more specifically the impact of the existence of a degree-of-freedom and oscillations in a given direction, on the fluid force and structural response in the perpendicular direction, do not seem to be systematically connected to changes in wake topology. Here, they are discussed in light of the orientation and magnitude of the instantaneous flow velocity seen by the moving body.
Simon Gsell, Rémi Bourguet, Marianna Braza. One- versus two-degree-of-freedom vortex-induced vibrations of a circular cylinder at Re=3900. Journal of Fluids and Structures, 2019, 85, pp.165-180. ⟨10.1016/j.jfluidstructs.2019.01.006⟩. ⟨hal-02062155⟩
Benjamin Bugeat, Jean-Camille Chassaing, Jean-Christophe Robinet, Pierre Sagaut. 3D global optimal forcing and response of the supersonic boundary layer. Journal of Computational Physics, 2019, 398, pp.108888. ⟨10.1016/j.jcp.2019.108888⟩. ⟨hal-02462825⟩ Plus de détails...
3D optimal forcing and response of a 2D supersonic boundary layer are obtained by computing the largest singular value and the associated singular vectors of the global resolvent matrix. This approach allows to take into account both convective-type and component-type non-normalities responsible for the non-modal growth of perturbations in noise selective amplifier flows. It is moreover a fully non-parallel approach that does not require any particular assumptions on the baseflow. The numerical method is based on the explicit calculation of the Jacobian matrix proposed by Mettot et al. [1] for 2D perturbations. This strategy uses the numerical residual of the compressible Navier-Stokes equations imported from a finite-volume solver that is then linearised employing a finite difference method. Extension to 3D perturbations, which are expanded into modes of wave number, is here proposed by decomposing the Jacobian matrix according to the direction of the derivatives contained in its coefficients. Validation is performed on a Blasius boundary layer and a supersonic boundary layer, in comparison respectively to global and local results. Application of the method to a boundary layer at M = 4.5 recovers three regions of receptivity in the frequency-transverse wave number space. Finally, the energy growth of each optimal response is studied and discussed.
Benjamin Bugeat, Jean-Camille Chassaing, Jean-Christophe Robinet, Pierre Sagaut. 3D global optimal forcing and response of the supersonic boundary layer. Journal of Computational Physics, 2019, 398, pp.108888. ⟨10.1016/j.jcp.2019.108888⟩. ⟨hal-02462825⟩
Marcello Meldi, Lyazid Djenidi, Robert Antonia. Reynolds number effect on the velocity derivative flatness factor. Journal of Fluid Mechanics, 2018, 856, pp.426-433. ⟨10.1017/jfm.2018.717⟩. ⟨hal-02114615⟩ Plus de détails...
Marcello Meldi, Lyazid Djenidi, Robert Antonia. Reynolds number effect on the velocity derivative flatness factor. Journal of Fluid Mechanics, 2018, 856, pp.426-433. ⟨10.1017/jfm.2018.717⟩. ⟨hal-02114615⟩
Giorgio Giorgiani, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-02114246⟩ Plus de détails...
Progressing toward more accurate and more efficient numerical codes forthe simulation of transport and turbulence in the edge plasma of tokamaks,we propose in this work a new hybrid discontinous Galerkin solver. Basedon 2D advection-diffusion conservation equations for the ion density and theparticle flux in the direction parallel to the magnetic field, the code simulatesplasma transport in the poloidal section of tokamaks, including the open fieldlines of the Scrape-off Layer (SOL) and the closed field lines of the core re-gion. The spatial discretization is based on a high-order hybrid DG schemeon unstructured meshes, which provides an arbitrary high-order accuracywhile reducing considerably the number of coupled degrees of freedom witha local condensation process. A discontinuity sensor is employed to identifycritical elements and regularize the solution with the introduction of artificialdiffusion. Based on a finite-element discretization, not constrained by a flux-aligned mesh, the code is able to describe plasma facing components of anycomplex shape using Bohm boundary conditions and to simulate the plasmain versatile magnetic equilibria, possibly extended up to the center. Nu-merical tests using a manufacturated solution show appropriate convergenceorders when varying independently the number of elements or the degree ofinterpolation. Validation is performed by benchmarking the code with thewell-referenced edge transport code SOLEDGE2D (Bufferandet al.2013,2015 [1, 2]) in the WEST geometry. Final numerical experiments show thecapacity of the code to deal with low-diffusion solutions.
Giorgio Giorgiani, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Frédéric Schwander, et al.. A hybrid discontinuous Galerkin method for tokamak edge plasma simulations in global realistic geometry. Journal of Computational Physics, 2018, 374, pp.515-532. ⟨10.1016/j.jcp.2018.07.028⟩. ⟨hal-02114246⟩
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, 2018, 195, pp.89-103. ⟨10.1016/j.atmosenv.2018.09.040⟩. ⟨hal-02114676⟩ Plus de détails...
This study assesses the performance of a large eddy simulation (LES) based on the lattice Boltzmann method (LBM) in predicting near field dispersion in street canyons with tree planting. Based on a benchmark test case benefiting from wind tunnel measurements (CODASC), this study qualitatively and quantitatively discusses the prediction of traffic-induced pollutant concentration with respect to several reference studies. It also analyses the physics of the flow and concentration fields. Although the problem might seem rather simple, the flow is highlighted to be strongly three dimensional and transient. These properties enhance pollutant dispersion in the empty street canyon but air flow velocity and turbulence intensity tend to decrease in tree crowns. This effect of trees increases both mean and peak concentration levels at pedestrian level, which may be problematic in cities with dense traffic. These results show that LBM-LES is particularly well suited to study dispersion problems towards the development of more breathable cities.
Lucie Merlier, Jérôme Jacob, Pierre Sagaut. Lattice-Boltzmann Large-Eddy Simulation of pollutant dispersion in street canyons including tree planting effects. Atmospheric Environment, 2018, 195, pp.89-103. ⟨10.1016/j.atmosenv.2018.09.040⟩. ⟨hal-02114676⟩
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-02114308⟩ Plus de détails...
A new Lattice Boltzmann collision model for large eddy simulation (LES) of weakly compressible flows is proposed. This model, referred to as the Hybrid Recursive Regularised Bhatnagar-Gross-Krook (HRR-BGK) model, is based on a modification of previously existing regularised collision models defined with the BGK Lattice Boltzmann method (LBM) framework. By hybridising the computation of the velocity gradient with an adequate Finite Difference scheme when reconstructing the non-equilibrium parts of the distribution function , a hyperviscosity term is introduced in the momentum equation, whose amplitude can be explicitly tuned via a weighting parameter. A dynamic version of the HRR-BGK is also proposed, in which the control parameter is tuned at each grid point and each time step in order to recover an arbitrarily fixed total dissipation. This new collision model is assessed for both explicit and implicit LES considering the flow around a circular cylinder at Re = 3900. The dynamic HRR-BGK is observed to yield very accurate results when equipped with Vreman's subgrid model to compute the target dissipation.
Jérôme Jacob, Orestis Malaspinas, Pierre Sagaut. A new hybrid recursive regularised Bhatnagar–Gross–Krook collision model for Lattice Boltzmann method-based large eddy simulation. Journal of Turbulence, 2018, pp.1 - 26. ⟨10.1080/14685248.2018.1540879⟩. ⟨hal-02114308⟩
Philippe Ghendrih, Y. Asahi, E. Caschera, Guilhem Dif-Pradalier, P. Peter Donnel, et al.. Generation and dynamics of SOL corrugated profiles. Journal of Physics: Conference Series, 2018, 1125, pp.012011. ⟨10.1088/1742-6596/1125/1/012011⟩. ⟨hal-02196677⟩ Plus de détails...
The staircase transport regime reported in kinetic simulations of plasma turbulent transport in magnetic confinement is recovered with a simple 2D fluid model allowing for reduced damping of the zonal flows. Some of the complex dynamics of the kinetic zonation regime are recovered but the pattern of the corrugation appears to be sinusoidal with a characteristic scale comparable to that of turbulence modes with largest spectral energy, in contrast to regimes observed in global and flux-driven kinetic simulations. Enhanced zonal flows govern both an overall reduction of the SOL width and a gradual steepening of the gradients with distance to the separatrix.
Philippe Ghendrih, Y. Asahi, E. Caschera, Guilhem Dif-Pradalier, P. Peter Donnel, et al.. Generation and dynamics of SOL corrugated profiles. Journal of Physics: Conference Series, 2018, 1125, pp.012011. ⟨10.1088/1742-6596/1125/1/012011⟩. ⟨hal-02196677⟩
Cédric Reux, Sébastien Kahn, L. Zani, Bernard Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, 2018, 136, pp.1572-1576. ⟨10.1016/j.fusengdes.2018.05.059⟩. ⟨hal-02115524⟩ Plus de détails...
The next step for fusion energy after the ITER tokamak is the demonstration power plant DEMO. In this framework , system codes are used to address high-level key design issues for the DEMO pre-conceptual phase. They aim at capturing the interactions between the subsystems of a fusion reactor. SYCOMORE is a modular system code which includes physics and technology models coupled to an optimizer in order to explore a large design parameter space. In the present paper, trade-off studies focused on technology modules are reported including the influence of some design-driving assumptions on the reactor performances and size, starting from a European DEMO1-like design (more than 500 MW net electric power and 2 h burn duration). The increase of the mechanical stress limits in TF and CS magnets can help reducing the reactor size, slightly more when high temperature superconductors are used in the TF coil. The tritium breeding ratio can be improved to more than 1.10 by a moderate increase of the size, but the tritium burn-up ratio needs one additional meter of major radius for every percent increase. Divertor coolant options are also compared, showing some differences between helium, hot and cold water scenarios at various incident divertor heat fluxes.
Cédric Reux, Sébastien Kahn, L. Zani, Bernard Pégourié, N. Piot, et al.. DEMO design using the SYCOMORE system code: Influence of technological constraints on the reactor performances. Fusion Engineering and Design, 2018, 136, pp.1572-1576. ⟨10.1016/j.fusengdes.2018.05.059⟩. ⟨hal-02115524⟩
Maria-Vittoria Salvetti, Marcello Meldi, Luca Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. Direct and Large-Eddy Simulation X, 24, pp.15-23, 2018. ⟨hal-02115804⟩ Plus de détails...
Maria-Vittoria Salvetti, Marcello Meldi, Luca Bruno, Pierre Sagaut. Reliability of Large-Eddy Simulations: Benchmarking and Uncertainty Quantification. Direct and Large-Eddy Simulation X, 24, pp.15-23, 2018. ⟨hal-02115804⟩
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, 2018, 60 (10), pp.105007. ⟨10.1088/1361-6587/aad650⟩. ⟨hal-02111781⟩ Plus de détails...
The impact of the del B-drift in the cross-field transport and its effect on the density and power scrape-off layer (SOL) width in the limit of low anomalous transport is studied with the fluid code SolEdge2D. In the first part of the work, the simulations are run with an isothermal reduced fluid model. It is found that a del B-drift dominated regime is reached in all geometries studied (JET-like, ASDEX-like and circular analytic geometries), and that the transition toward this regime comes along with the apparition of supersonic shocks, and a complex parallel equilibrium. The parametric dependencies of the SOL width in this regime are investigated, and the temperature and the poloidal magnetic field are found to be the principal parameters governing the evolution of the SOL width. In the second part of this paper, the impact of additional physics is studied (inclusion of the centrifugal drift, self-consistent variation of temperature and the treatment of the neutral species). The addition of centrifugal drift and neutral species are shown to play a role in the establishment of the parallel equilibrium, impacting the SOL's width, although the role of the centrifugal drift is limited to a low diffusion level. Finally, the numerical results are compared with the estimate of the Goldston's heuristic drift based model (HD-model), the starting point of our study, and which has shown good agreement with experimental scaling laws. We find that the particles SOL widths in the del B-drift dominated regime are at least two times smaller than the estimate of the HD-model. Moreover, in the parametric dependencies proposed by the HD-model, the dependency with B-pol is retrieved, but not the one on T.
Camille Baudoin, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, et al.. Drift driven cross-field transport and scrape-off layer width in the limit of low anomalous transport. Plasma Physics and Controlled Fusion, 2018, 60 (10), pp.105007. ⟨10.1088/1361-6587/aad650⟩. ⟨hal-02111781⟩
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, 2018, 125, pp.1379-1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-02114047⟩ Plus de détails...
A new thermal lattice Boltzmann (LB) method is proposed for the simulation of natural convection with large temperature differences and high Rayleigh number. A regularization procedure is developed on LB equation with a third order expansion of equilibrium distribution functions, in which a temperature term is involved to recover the equation of state for perfect gas. A hybrid approach is presented to couple mass conservation equation, momentum conservation equations and temperature evolution equation. A simple and robust non-conservative form of temperature transport equation is adopted and solved by the finite volume method. A comparison study between classical Double Distribution Function (DDF) model and the hybrid finite volume model with different integration schemes is presented to demonstrate both consistency and accuracy of hybrid models. The proposed model is assessed by simulating several test cases, namely the two-dimensional non-Boussinesq natural convection in a square cavity with large horizontal temperature differences and two unsteady natural convection flows in a tall enclosure at high Rayleigh number. The present method can accurately predict both the steady and unsteady non-Boussinesq convection flows with significant heat transfer. For unsteady natural convection, oscillations with chaotic feature can be well captured in large temperature gradient conditions.
Yong-Liang Feng, Shao-Long Guo, Wen-Quan Tao, Pierre Sagaut. Regularized thermal lattice Boltzmann method for natural convection with large temperature differences. International Journal of Heat and Mass Transfer, 2018, 125, pp.1379-1391. ⟨10.1016/j.ijheatmasstransfer.2018.05.051⟩. ⟨hal-02114047⟩
Journal: International Journal of Heat and Mass Transfer
Yongliang Feng, Muhammad Tayyab, Pierre Boivin. A Lattice-Boltzmann model for low-Mach reactive flows. Combustion and Flame, 2018, 196, pp.249 - 254. ⟨10.1016/j.combustflame.2018.06.027⟩. ⟨hal-01832640⟩ Plus de détails...
A new Lattice-Boltzmann model for low-Mach reactive flows is presented. Based on standard lattices, the model is easy to implement, and is the first, to the authors' knowledge, to pass the classical freely propagating flame test case as well as the counterflow diffusion flame, with strains up to extinction. For this presentation, simplified transport properties are considered, each species being assigned a separate Lewis number. In addition, the gas mixture is assumed to be calorically perfect. Comparisons with reference solutions show excellent agreement for mass fraction profiles, flame speed in premixed mixtures, as well as maximum temperature dependence with strain rate in counterflow diffusion flames.
Yongliang Feng, Muhammad Tayyab, Pierre Boivin. A Lattice-Boltzmann model for low-Mach reactive flows. Combustion and Flame, 2018, 196, pp.249 - 254. ⟨10.1016/j.combustflame.2018.06.027⟩. ⟨hal-01832640⟩
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, 2018, 56 (9), pp.3622-3635. ⟨10.2514/1.J056405⟩. ⟨hal-02113987⟩ Plus de détails...
This paper describes a methodology, called local decomposition method, which aims at building a surrogate model based on steady turbulent aerodynamic fields at multiple operating conditions. The various shapes taken by the aerodynamic fields due to the multiple operation conditions pose real challenges as well as the computational cost of the high-fidelity simulations. The developed strategy mitigates these issues by combining traditional surrogate models and machine learning. The central idea is to separate the solutions with a subsonic behavior from the transonic and high-gradient solutions. First, a shock sensor extracts a feature corresponding to the presence of discontinuities, easing the clustering of the simulations by an unsupervised learning algorithm. Second, a supervised learning algorithm divides the parameter space into subdomains, associated to different flow regimes. Local reduced-order models are built on each subdomain using proper orthogonal decomposition coupled with a multivariate interpolation tool. Finally, an improved resampling technique taking advantage of the subdomain decomposition minimizes the redundancy of sampling. The methodology is assessed on the turbulent two-dimensional flow around the RAE2822 transonic airfoil. It exhibits a significant improvement in terms of prediction accuracy for the developed strategy compared with the classical method of surrogate modeling.
Romain Dupuis, Jean-Christophe Jouhaud, Pierre Sagaut. Surrogate Modeling of Aerodynamic Simulations for Multiple Operating Conditions Using Machine Learning. AIAA Journal, 2018, 56 (9), pp.3622-3635. ⟨10.2514/1.J056405⟩. ⟨hal-02113987⟩
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators Sensitivity of State Estimation to Density of Time Sampling for Available Observation. Flow, Turbulence and Combustion, 2018, 101 (2), pp.389-412. ⟨10.1007/s10494-018-9967-6⟩. ⟨hal-02114575⟩ Plus de détails...
A sensitivity analysis of new methodological approaches for state estimation (Meldi and Poux J. Comput. Phys. 347, 207-234, 2017) is proposed in this manuscript. The performance of the estimator is tested via the analysis of a number of aspects that play a major role in the augmented prediction process, such as the density in time sampling of available observation, the placement of sensors and the interaction with boundary conditions. The work is developed for the turbulent spatially evolving mixing layer test case, using high precision DNS samples as observation and Smagorinsky LES as underlying model. A number of estimators combining LES with DNS data integrated via sensors are performed, varying the frequency of time sampling of observation f T = 1// T , where T is the period between successive assimilation phases. It is concluded that if T ≤≈ 0.5t A , where t A is the characteristic average advection time, the prediction via estimator shows minimal differences i.e. the process of state estimation has reached convergence. This relation can be interpreted as a threshold for converged state estimation. However, the results show as well that a linear converge towards pure model performance is not obtained for every physical quantity with progressive decrease of f T , while eventually pure model results are obtained for f T → 0. In addition, the effect of upstream boundary conditions over the state estimation are investigated and strategies for optimized positions of sensors are derived.
Marcello Meldi. Augmented Prediction of Turbulent Flows via Sequential Estimators Sensitivity of State Estimation to Density of Time Sampling for Available Observation. Flow, Turbulence and Combustion, 2018, 101 (2), pp.389-412. ⟨10.1007/s10494-018-9967-6⟩. ⟨hal-02114575⟩
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-02116002⟩ Plus de détails...
Variations in the local stability of the flow in a Taylor-Couette cell can be imposed by adding an axial Poiseuille flow and a radial flow associated with one or both of the cylinders being permeable. At a given rotation rate of the inner cylinder, this results in adjacent regions of the flow that can be simultaneously stable, convectively unstable, and absolutely unstable, making this system fit for studying global modes of instability. To this end, building on the existing stability analysis in absolute modes developing over axially invariant base flows, we consider the case of axially varying base flows in systems for which the outer cylinder is impermeable, and the inner cylinder is a weakly permeable membrane through which the radial flow is governed by Darcy's law. The frameworks of linear and nonlinear global modes are used to describe the instabilities and assess the results of direct numerical simulations using a dedicated pseudospectral method. Three different axially evolving set-ups are considered. In the first, fluid injection occurs along the full inner cylinder. In the second, fluid extraction occurs along the full inner cylinder. Besides its fundamental interest, this set-up is relevant to filtration devices. In the third, fluid flux through the inner cylinder evolves from extraction to injection as cross-flow reversal occurs. In agreement with the global mode analyses, the numerical simulations develop centrifugal instabilities above the predicted critical rotation rates and downstream of the predicted axial locations. The global mode analyses do not fully explain, however, that. the instabilities observed in the numerical simulations take the form of axial stacks of wavepackets characterized by jumps of the temporal frequency.
Nils Tilton, Denis Martinand. Taylor–Couette–Poiseuille flow with a weakly permeable inner cylinder: absolute instabilities and selection of global modes. Journal of Fluid Mechanics, 2018, 849, pp.741 - 776. ⟨10.1017/jfm.2018.437⟩. ⟨hal-02116002⟩
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-02116221⟩ Plus de détails...
The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Karman self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counter-clockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m is an element of [32, 78 ]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M. Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity. Journal of Fluid Mechanics, 2018, 848, pp.631 - 647. ⟨10.1017/jfm.2018.239⟩. ⟨hal-02116221⟩
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, 2018, 58 (6-8), pp.511-517. ⟨10.1002/ctpp.201700163⟩. ⟨hal-02111708⟩ Plus de détails...
In this paper, a κ−ϵ transport model is presented as a turbulence reduction tool for a typical ohmic L‐mode discharge plasma in a divertor‐configurated tokamak. Taking a Tokamak à configuration variable (TCV) study case, a feedback loop procedure is performed using the SolEdge2D code to acquire plasma diffusivity at the outer mid‐plane. The κ−ϵ model is calibrated through its free parameters with the aim of recovering the diffusivity calculated in the feedback procedure. Finally, it is shown that the model can self‐consistently calculate diffusivity in the whole domain, recovering the poloidal asymmetries due to interchange instabilities.
Serafina Baschetti, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Optimization of turbulence reduced model free parameters based on L-mode experiments and 2D transport simulations. Contributions to Plasma Physics, 2018, 58 (6-8), pp.511-517. ⟨10.1002/ctpp.201700163⟩. ⟨hal-02111708⟩
Hugo Bufferand, Guido Ciraolo, Pierfrancesco Di Cintio, Nicolas Fedorczak, Philippe Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, 2018, 58 (6-8), pp.563-569. ⟨10.1002/ctpp.201700162⟩. ⟨hal-02112673⟩ Plus de détails...
The non-local expression proposed by Luciani-Mora-Virmont is implemented in a one dimensional fluid model for the scrape-off layer. Analytical solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The non-local heat flux is compared to the Spitzer-Härm heat flux for different collisionality. KEYWORDS heat conduction, non-local transport, plasma physics 1 INTRODUCTION At the entrance of the scrape-off layer, the plasma collisionality í µí¼ ⋆ defined as the ratio between the field line length and collision mean free path is found to be of order unity. Despite this low collisionality, the tokamak edge plasma modelling relies mostly on the fluid approach and collisional closures that are theoretically only valid at high collisionality. Departure between Braginskii fluid description and kinetic modelling has been highlighted, particularly an underestimation of temperature gradient by the fluid approach. [1] Several kinetic corrections have been proposed to improve the plasma description at intermediate collisionality. [2-5] In this contribution, we investigate kinetic corrections to the local Spitzer-Härm (Braginskii) closure for the heat flux; more precisely, we focus on applying the non-local expression for the heat flux proposed by Luciani-Mora-Virmont [6] to scrape-off layer physics. In particular, we adapt boundary conditions and implement the non-local expression into a 1D hydrodynamic model for the scrape-off layer.
Hugo Bufferand, Guido Ciraolo, Pierfrancesco Di Cintio, Nicolas Fedorczak, Philippe Ghendrih, et al.. Non-local heat flux application for scrape-off layer plasma. Contributions to Plasma Physics, 2018, 58 (6-8), pp.563-569. ⟨10.1002/ctpp.201700162⟩. ⟨hal-02112673⟩
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, 2018, 58 (6-8), pp.457-464. ⟨10.1002/ctpp.201700222⟩. ⟨hal-02113953⟩ Plus de détails...
In order to improve the presently used ad hoc flux limiter treatment of parallel heat flux transport in edge plasma fluid codes, here, we consider a generalized version of the Fourier law implementing a non-local kernel for the heat flux computation. The Bohm boundary condition at the wall is recovered, introducing a volumetric loss term representing the contribution of suprathermal particles to the energy out flux. As expected, this contribution is negligible in the strongly collisional regime, while it becomes more and more dominant for marginally and low-collisional regimes. In the second part of the paper, we consider a kinetic approach where collisions are considered using the multi-particle collision algorithm. Kinetic simulation results at medium and low collisionality are also reported.
Guido Ciraolo, Hugo Bufferand, Pierfrancesco Di Cintio, Philippe Ghendrih, Stefano Lepri, et al.. Fluid and kinetic modelling for non-local heat transport in magnetic fusion devices. Contributions to Plasma Physics, 2018, 58 (6-8), pp.457-464. ⟨10.1002/ctpp.201700222⟩. ⟨hal-02113953⟩
Matteo Valentinuzzi, Giorgio Giorgiani, Yannick Marandet, Hugo Bufferand, Guido Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, 2018, 58 (6-8), pp.710-717. ⟨10.1002/ctpp.201700211⟩. ⟨hal-02116176⟩ Plus de détails...
A new neutral fluid code has been developed as a necessary step towards a hybrid fluid/kinetic neutral model, to be used in ITER or DEMO simulations, where part of the divertor will be very collisional for neutrals. The neutral fluid code, which is able to handle complex geometries in view of the coupling to Soledge2D, is tested on plasma backgrounds obtained by Soledge2D‐Eirene in WEST geometry, for different divertor regimes, and is found to be in fair agreement with the kinetic Monte Carlo solver Eirene. The differences are due to the simplifications introduced in the fluid model and to the fact that a fluid description is not fully valid in these cases.
Matteo Valentinuzzi, Giorgio Giorgiani, Yannick Marandet, Hugo Bufferand, Guido Ciraolo, et al.. Fluid description of neutral particles in divertor regimes in WEST. Contributions to Plasma Physics, 2018, 58 (6-8), pp.710-717. ⟨10.1002/ctpp.201700211⟩. ⟨hal-02116176⟩
Dongmei Fan, Yannick Marandet, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, 2018, 58 (6-8), pp.490-496. ⟨10.1002/ctpp.201700216⟩. ⟨hal-02114027⟩ Plus de détails...
The three-dimensional (3D) turbulence code TOKAM3X-EIRENE, coupling the 3D non-isothermal version of TOKAM3X to the EIRENE Monte Carlo solver has been developed with the ability to simulate self-consistently the interactions between large-scale flows and turbulence both in limited and diverted plasmas, including recycling. This is especially important for diverted plasmas, where neutrals play a key role and where the recycling source is strongly dominant. The code package relies on the same interface as the Soledge2D-EIRENE code, which retains state-of-the-art plasma-wall interaction, as well as atomic and molecular physics. In this paper, we present the first results obtained in WEST divertor geometry, in laminar mode, with the aim of verifying the new code package. The divertor density regimes are recovered, and the code results are shown to be consistent with the results of the two-point model, thus opening the way for turbulent simulations.
Dongmei Fan, Yannick Marandet, Patrick Tamain, Hugo Bufferand, Guido Ciraolo, et al.. Self-consistent coupling of the three-dimensional fluid turbulence code TOKAM3X and the kinetic neutrals code EIRENE. Contributions to Plasma Physics, 2018, 58 (6-8), pp.490-496. ⟨10.1002/ctpp.201700216⟩. ⟨hal-02114027⟩
Nicolas Nace, Patrick Tamain, Camille Baudoin, Hugo Bufferand, Guido Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, 2018, 58 (6-8), pp.497-504. ⟨10.1002/ctpp.201700174⟩. ⟨hal-02115405⟩ Plus de détails...
The impact of magnetic configuration on edge turbulence properties in circular limiter geometry is investigated using TOKAM3X, a three-dimensional (3D), first-principle, fluid code for edge plasma. The theoretical spatial tilting of magnetic shear on turbulence fluctuations is recovered. Magnetic shear is found to generate or enhance poloidal high/low field sides (HFS/LFS) and up/down asymmetries. A simulation mimicking the impact of an X-point on circular limiter geometry leads to the formation of two transport barriers that are stable in time, thus leading to the improvement of core particle confinement and to reduction of radial turbulent transport. The magnetic shear, which also strongly enhances the E × B shear, is responsible for the barrier formation.
Nicolas Nace, Patrick Tamain, Camille Baudoin, Hugo Bufferand, Guido Ciraolo, et al.. Impact of safety factor and magnetic shear profiles on edge turbulence in circular limited geometry. Contributions to Plasma Physics, 2018, 58 (6-8), pp.497-504. ⟨10.1002/ctpp.201700174⟩. ⟨hal-02115405⟩
Jérôme Jacob, Pierre Sagaut. Wind comfort assessment by means of large eddy simulation with lattice Boltzmann method in full scale city area. Building and Environment, 2018, 139, pp.110 - 124. ⟨10.1016/j.buildenv.2018.05.015⟩. ⟨hal-02114339⟩ Plus de détails...
Large-eddy simulations based on the Lattice-Boltzmann method of the flow in a realistic, full scale urban area are performed to compare several wind comfort criteria. It is observed that popular criteria for pedestrian comfort lead to very different conclusions, due to the access to high spatio-temporal resolution data. Different mixed strategies based on the combination of several criteria are proposed and compared to enhance pedestrian wind comfort assessment in practical cases.
Jérôme Jacob, Pierre Sagaut. Wind comfort assessment by means of large eddy simulation with lattice Boltzmann method in full scale city area. Building and Environment, 2018, 139, pp.110 - 124. ⟨10.1016/j.buildenv.2018.05.015⟩. ⟨hal-02114339⟩
Laurent Valade, Annika Ekedahl, Philippe Ghendrih, Yanick Sarazin, Yuuichi Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02116142⟩ Plus de détails...
Hotspot generation by lower-hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function. An island structure is formed in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response, driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function, with extent reaching one thermal velocity, is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of the small-scale features generated by the LH launchers, which are responsible for the interaction with the cold electrons. This mechanism can trigger hotspot generation further in the scrape-off layer than otherwise expected.
Laurent Valade, Annika Ekedahl, Philippe Ghendrih, Yanick Sarazin, Yuuichi Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02116142⟩
L Valade, A. Ekedahl, P Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02196679⟩ Plus de détails...
Hot spot generation by Lower Hybrid (LH) launchers is found to be governed by a resonance in the plasma electric field response to the external drive. The kinetic analysis in 1D-1V in the parallel direction allows one to compute the amplification effect for small amplitude of the external drive. The resonant Lorentzian response distorts the distribution function with an island structure in the suprathermal part at the phase velocity of the external electrostatic drive. The non-linear features enhance the plasma response driving overlap effects between multiple waves at rather low amplitude. The onset of a plateau in the distribution function with extent up to one thermal velocity is already obtained when the standard overlap condition is achieved. The sensitivity of the resonance to plasma parameters and large variation of the amplification magnitude can compensate the fast radial decay of 1
L Valade, A. Ekedahl, P Ghendrih, Y. Sarazin, Y. Asahi, et al.. Electron burst driven by near electric field effects of lower-hybrid launchers. Contributions to Plasma Physics, 2018, 58 (6-8), pp.465-470. ⟨10.1002/ctpp.201700156⟩. ⟨hal-02196679⟩
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Pierre Sagaut, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, 2018, 19 (7), pp.570-599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-02112204⟩ Plus de détails...
In this work, the spectral modelling developed in MCS [Mons, Cambon, Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically-averaged descriptors. J Fluid Mech. 2016;788:147-182] for shear-driven turbulence is further analysed and then improved. First, using self-similarity arguments, it is shown that the asymptotic kinetic energy exponential growth rate is independent of the large scales infrared slope sigma, with, unlike unstably stratified homogeneous turbulence where strongly depends on sigma. The MCS model relies on the truncation at the second order of the spectral two-point velocity correlation expansion into spherical harmonics. The expansion is here pursued at the next even order, the fourth one: the noteworthy consequence is that is decreased compared to MCS and is thus closer to values obtained in direct numerical simulations and experiments. Finally, some analytical considerations about odd-order contributions in the expansion of polarisation anisotropy are proposed.
Antoine Briard, Benoît-Joseph Gréa, Vincent Mons, Claude Cambon, Pierre Sagaut, et al.. Advanced spectral anisotropic modelling for shear flows. Journal of Turbulence, 2018, 19 (7), pp.570-599. ⟨10.1080/14685248.2018.1478092⟩. ⟨hal-02112204⟩
Jean-François Boussuge, Mathieu Catchirayer, J.-F Boussuge, Pierre Sagaut, Marc Montagnac, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112710⟩ Plus de détails...
Wall-modeling is required to make large-eddy simulations of high-Reynolds number wall-bounded turbulent flows feasible in terms of computational cost. Here, an extension of the integral wall-model for large-eddy simulations (iWMLESs) for incompressible flows developed by Yang et al. ["Integral wall model for large eddy simulations of wall-bounded turbulent flows," Phys. Fluids 27(2), 025112 (2015)] to compressible and isothermal flows is proposed and assessed. The iWMLES approach is analogous to the von Karman-Pohlhausen integral method for laminar flows: the velocity profile is parameterized, and unknown coefficients are determined by matching boundary conditions obeying the integral boundary layer momentum equation. It allows non-equilibrium effects such as pressure gradient and convection to be included at a computing cost similar to analytical wall-models. To take into account density variations and temperature gradients, the temperature profile is also parameterized and the integral compressible boundary layer energy equation is considered. Parameterized profiles are based on the usual logarithmic wall functions with corrective terms to extend their range of validity. Instead of solving a set of differential equations as wall-models based on the thin boundary layer equation approach, a simple linear system is solved. The proposed wall-model is implemented in a finite-volume cell-centered structured grid solver and assessed on adiabatic and isothermal plane channel flows at several friction Reynolds and Mach numbers. For low Mach number cases, mean profiles, wall fluxes, and turbulent fluctuations are in agreement with those of Direct Numerical Simulation (DNS). For supersonic flows, the results are in good agreement with the DNS data, especially the mean velocity quantities and the wall friction, while standard analytical wall-models show their limits.
Jean-François Boussuge, Mathieu Catchirayer, J.-F Boussuge, Pierre Sagaut, Marc Montagnac, et al.. Extended integral wall-model for large-eddy simulations of compressible wall-bounded turbulent flows. Physics of Fluids, 2018, 30 (6), pp.065106. ⟨10.1063/1.5030859⟩. ⟨hal-02112710⟩
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-02116210⟩ Plus de détails...
In this paper, an explicit wall model based on a power-law velocity profile is proposed for the simulation of the incompressible flow around airfoils at high Reynolds numbers. This wall model is particularly suited for the wall treatment involved in Cartesian grids. Moreover, it does not require an iterative procedure for the friction velocity determination. The validation of this power-law wall model is assessed for Reynolds-averaged Navier-Stokes simulations of the flow around a two-dimensional airfoil using the lattice Boltzmann approach along with the Spalart-Allmaras turbulence model. Good results are obtained for the prediction of the aerodynamic coefficients and the pressure profiles at two Reynolds numbers and several angles of attack. The explicit power-law is thus well suited for a simplified near-wall treatment at high Reynolds numbers using Cartesian grids.
Sylvia Wilhelm, Jérôme Jacob, Pierre Sagaut. An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils. Physics of Fluids, 2018, 30 (6), pp.065111. ⟨10.1063/1.5031764⟩. ⟨hal-02116210⟩
Zhe Li, Julien Favier. Fluid-Structure Interaction Using Lattice Boltzmann Method Coupled With Finite Element Method. Analysis and Applications of Lattice Boltzmann Simulations, 2018. ⟨hal-02887325⟩ Plus de détails...
Zhe Li, Julien Favier. Fluid-Structure Interaction Using Lattice Boltzmann Method Coupled With Finite Element Method. Analysis and Applications of Lattice Boltzmann Simulations, 2018. ⟨hal-02887325⟩
Jessica Sari, Francesco Cremonesi, Mehdi Khalloufi, François Cauneau, Philippe Meliga, et al.. Anisotropic adaptive stabilized finite element solver for RANS models. International Journal for Numerical Methods in Fluids, 2018, 86 (11), pp.717-736. ⟨10.1002/fld.4475⟩. ⟨hal-02115828⟩ Plus de détails...
Aerodynamic characteristics of various geometries are predicted using a finite element formulation coupled with several numerical techniques to ensure stability and accuracy of the method. First, an edge based error estimator and anisotropic mesh adaptation are used to detect automatically all flow features under the constraint of a fixed number of elements, thus controlling the computational cost. A Variational MultiScale stabilized finite element method is employed to solve the incompressible Navier-Stokes equations. Finally, the Spalart-Allmaras turbulence model is solved using the Streamline Upwind Petrov-Galerkin (SUPG) method. This paper is meant to show that the combination of anisotropic unsteady mesh adaptation with stabilized finite element methods provides an adequate framework for solving turbulent flows at high Reynolds numbers. The proposed method was validated on several test cases by confrontation with literature of both numerical and experimental results, in terms of accuracy on the prediction of the drag and lift coefficients as well as their evolution in time for unsteady cases. This article is protected by copyright. All rights reserved.
Jessica Sari, Francesco Cremonesi, Mehdi Khalloufi, François Cauneau, Philippe Meliga, et al.. Anisotropic adaptive stabilized finite element solver for RANS models. International Journal for Numerical Methods in Fluids, 2018, 86 (11), pp.717-736. ⟨10.1002/fld.4475⟩. ⟨hal-02115828⟩
Journal: International Journal for Numerical Methods in Fluids
Myriam Slama, Cédric Leblond, Pierre Sagaut. A Kriging-based elliptic extended anisotropic model for the turbulent boundary layer wall pressure spectrum. Journal of Fluid Mechanics, 2018, 840, pp.25 - 55. ⟨10.1017/jfm.2017.810⟩. ⟨hal-02115966⟩ Plus de détails...
The present study addresses the computation of the wall pressure spectrum for a turbulent boundary layer flow without pressure gradient, at high Reynolds numbers, using a new model, the Kriging-based elliptic extended anisotropic model (KEEAM). A space–time solution to the Poisson equation for the wall pressure fluctuations is used. Both the turbulence–turbulence and turbulence–mean shear interactions are taken into account. It involves the mean velocity field and space–time velocity correlations which are modelled using Reynolds stresses and velocity correlation coefficients. We propose a new model, referred to as the extended anisotropic model, to evaluate the latter in all regions of the boundary layer. This model is an extension of the simplified anisotropic model of Gavin (PhD thesis, 2002, The Pennsylvania State University, University Park, PA) which was developed for the outer part of the boundary layer. It relies on a new expression for the spatial velocity correlation function and new parameters calibrated using the direct numerical simulation results of Sillero et al. (Phys. Fluids, vol. 26, 2014, 105109). Spatial correlation coefficients are related to space–time coefficients with the elliptic model of He & Zhang (Phys. Rev. E, vol. 73, 2006, 055303). The turbulent quantities necessary for the pressure computation are obtained by Reynolds-averaged Navier–Stokes solutions with a Reynolds stress turbulence model. Then, the pressure correlations are evaluated with a self-adaptive sampling strategy based on Kriging in order to reduce the computation time. The frequency and wavenumber–frequency wall pressure spectra obtained with the KEEAM agree well with empirical models developed for turbulent boundary layer flows without pressure gradient.
Myriam Slama, Cédric Leblond, Pierre Sagaut. A Kriging-based elliptic extended anisotropic model for the turbulent boundary layer wall pressure spectrum. Journal of Fluid Mechanics, 2018, 840, pp.25 - 55. ⟨10.1017/jfm.2017.810⟩. ⟨hal-02115966⟩
Pierre-Yves Passaggia, Uwe Ehrenstein. Optimal control of a separated boundary-layer flow over a bump. Journal of Fluid Mechanics, 2018, 840, pp.238 - 265. ⟨10.1017/jfm.2018.6⟩. ⟨hal-01708850⟩ Plus de détails...
Pierre-Yves Passaggia, Uwe Ehrenstein. Optimal control of a separated boundary-layer flow over a bump. Journal of Fluid Mechanics, 2018, 840, pp.238 - 265. ⟨10.1017/jfm.2018.6⟩. ⟨hal-01708850⟩
Elena Alekseenko, Bernard Roux. Numerical simulation of the wind influence on bottom shear stress and salinity fields in areas of Zostera noltei replanting in a Mediterranean coastal lagoon. Progress in Oceanography, 2018, 163, pp.147-160. ⟨10.1016/j.pocean.2017.05.001⟩. ⟨hal-02111578⟩ Plus de détails...
The paper concerns the numerical simulation of the wind influence on bottom shear stress and salinity fields in a semi-enclosed coastal lagoon (Etang de Berre) which is connected to the Mediterranean through a long and narrow channel (called Caronte). Two different scenarios are considered. The first scenario (scen.#1), starting with a homogeneous salinity of S = 20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from a hydropower plant (250 m 3 /s). Then, in the second scenario (scen.#2), we study how a strong wind of 80 km/h can destroy the haline stratification obtained at the end of scen.#1. The MARS3D numerical model is used to analyze the 3D current and salinity distribution induced by these three meteorological, oceanic and anthropogenic forcings in this lagoon and in the Caronte channel. The main goal is to determine the bottom shear stress (BSS) in the nearshore areas of Zostera noltei replanting, and to compare it with the threshold for erosion of the bottom sediments for different bottom roughness parameters. The most interesting results concern the four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.#2 show that all these areas are subject to a downwind coastal jet. The destratification process is very beneficial; salinity always remains greater than 12 PSU for a N-NW wind of 80 km/h and a hydropower runoff of 250 m 3 /s. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (where BSS = 0). When comparing the BSS value at the four control points with the critical value, BSS cr , at which the sediment mobility would occur, we see that for the smaller bottom roughness values (ranging from z 0 = 3.5 Â 10 À4 mm, to 3.5 Â 10 À2 mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40 km/h (which is blowing for around 100 days per year), BSS still largely surpasses BSS cr-at least for the silt sediments (ranging from z 0 = 3.5 Â 10 À4 mm, to 3.5 Â 10 À3 mm). This confirms the possibility that the coastal jet could be a stressor for SAV replanting.
Elena Alekseenko, Bernard Roux. Numerical simulation of the wind influence on bottom shear stress and salinity fields in areas of Zostera noltei replanting in a Mediterranean coastal lagoon. Progress in Oceanography, 2018, 163, pp.147-160. ⟨10.1016/j.pocean.2017.05.001⟩. ⟨hal-02111578⟩
D Rigamonti, L. Giacomelli, G Gorini, M. Nocente, M. Rebai, et al.. Neutron spectroscopy measurements of 14 MeV neutrons at unprecedented energy resolution and implications for deuterium–tritium fusion plasma diagnostics. Measurement Science and Technology, 2018, 29 (4), pp.045502. ⟨10.1088/1361-6501/aaa675⟩. ⟨hal-02177077⟩ Plus de détails...
An accurate calibration of the JET neutron diagnostics with a 14 MeV neutron generator was performed in the first half of 2017 in order to provide a reliable measurement of the fusion power during the next JET deuterium-tritium (DT) campaign. In order to meet the target accuracy, the chosen neutron generator has been fully characterized at the Neutron Metrology Laboratory of the National Physical Laboratory (NPL), Teddington, United Kingdom. The present paper describes the measurements of the neutron energy spectra obtained using a high-resolution single-crystal diamond detector (SCD). The measurements, together with a new neutron source routine 'ad hoc' developed for the MCNP code, allowed the complex features of the neutron energy spectra resulting from the mixed D/T beam ions interacting with the T/D target nuclei to be resolved for the first time. From the spectral analysis a quantitative estimation of the beam ion composition has been made. The unprecedented intrinsic energy resolution (<1% full width at half maximum (FWHM) at 14 MeV) of diamond detectors opens up new prospects for diagnosing DT plasmas, such as, for instance, the possibility to study non-classical slowing down of the beam ions by neutron spectroscopy on ITER.
D Rigamonti, L. Giacomelli, G Gorini, M. Nocente, M. Rebai, et al.. Neutron spectroscopy measurements of 14 MeV neutrons at unprecedented energy resolution and implications for deuterium–tritium fusion plasma diagnostics. Measurement Science and Technology, 2018, 29 (4), pp.045502. ⟨10.1088/1361-6501/aaa675⟩. ⟨hal-02177077⟩
Sylvain Chateau, Umberto d'Ortona, Sébastien Poncet, Julien Favier. Transport and Mixing Induced by Beating Cilia in Human Airways. Frontiers in Physiology, 2018, 9, pp.161. ⟨10.3389/fphys.2018.00161⟩. ⟨hal-01875672⟩ Plus de détails...
The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann-Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia aremodeled by a set of Lagrangian points, and Immersed Boundary forces are computed onto these points in order to ensure the no-slip velocity conditions between the cilia and the fluids. The cilia are immersed in a two-layer environment: the periciliary layer (PCL) and the mucus above it. The motion of the cilia is prescribed, as well as the phase lag between two cilia in order to obtain a typical collective motion of cilia, known as metachronal waves. The results obtained from a parametric study show that antiplectic metachronal waves are the most efficient regarding the fluid transport. A specific value of phase lag, which generates the larger mucus transport, is identified. The mixing is studied using several populations of tracers initially seeded into the pericilary liquid, in the mucus just above the PCL-mucus interface, and in the mucus far away from the interface. We observe that each zone exhibits different chaotic mixing properties. The larger mixing is obtained in the PCL layer where only a few beating cycles of the cilia are required to obtain a full mixing, while above the interface, the mixing is weaker and takes more time. Almost no mixing is observed within the mucus, and almost all the tracers do not penetrate the PCL layer. Lyapunov exponents are also computed for specific locations to assess how the mixing is performed locally. Two time scales are introduced to allow a comparison between mixing induced by fluid advection and by molecular diffusion. These results are relevant in the context of respiratory flows to investigate the transport of drugs for patients suffering from chronic respiratory diseases.
Sylvain Chateau, Umberto d'Ortona, Sébastien Poncet, Julien Favier. Transport and Mixing Induced by Beating Cilia in Human Airways. Frontiers in Physiology, 2018, 9, pp.161. ⟨10.3389/fphys.2018.00161⟩. ⟨hal-01875672⟩
Philippe Meliga, Edouard Boujo, Marcello Meldi, François Gallaire. Revisiting the drag reduction problem using adjoint-based distributed forcing of laminar and turbulent flows over a circular cylinder. European Journal of Mechanics - B/Fluids, 2018, 72, pp.123-134. ⟨10.1016/j.euromechflu.2018.03.009⟩. ⟨hal-02114650⟩ Plus de détails...
This study assesses the ability of a sensitivity-based, span-wise homogeneous control velocity distributed at the surface of a circular cylinder to cut down the cost of reducing drag by more classical techniques, e.g., base bleed and lateral suction. At Reynolds number Re = 100, achieving the linear optimal reduction requires a time-dependent control velocity, set at each time instant against the sensitivity of the instantaneous drag. This approach however fails against even small control amplitudes because the system does not have time to adjust to the rapid change in the value of the wall velocity, and drag essentially increases. An efficient (albeit linearly suboptimal) reduction is however achieved using a steady control velocity set against the time averaged sensitivity. By doing so, drag decreases monotonically with the control momentum coefficient, and the sensitivity-based design exhibits a significant advantage over base bleed and lateral suction, that both reduce drag to a far lesser extent. Similar results are reported using various levels of modeling to compute approximations to the exact, time averaged sensitivity. The mean flow approach, that requires knowledge of the sole time averaged cylinder flow, yields especially promising results given the marginal computational effort. This approach is thus extended to the turbulent case at Re = 3900, where it achieves similar efficiency in the frame of both 2-D and 3-D RANS modeling. The study concludes with a discussion about the feasibility to extend the scope to span-wise periodic forcing velocities, following the line of thought of Kim & Choi [Phys. Fluids 17, 033103 (2005)].
Philippe Meliga, Edouard Boujo, Marcello Meldi, François Gallaire. Revisiting the drag reduction problem using adjoint-based distributed forcing of laminar and turbulent flows over a circular cylinder. European Journal of Mechanics - B/Fluids, 2018, 72, pp.123-134. ⟨10.1016/j.euromechflu.2018.03.009⟩. ⟨hal-02114650⟩
Eunok Yim, J.-M Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, 2018, 836, pp.43-71. ⟨10.1017/jfm.2017.771⟩. ⟨hal-02121890⟩ Plus de détails...
This paper proposes a resolution to the conundrum of the roles of convective and absolute instability in transition of the rotating-disk boundary layer. It also draws some comparison with swept-wing flows. Direct numerical simulations based on the incompressible Navier–Stokes equations of the flow over the surface of a rotating disk with modelled roughness elements are presented. The rotating-disk flow has been of particular interest for stability and transition research since the work by Lingwood (J. Fluid Mech., vol. 299, 1995, pp. 17–33) where an absolute instability was found. Here stationary disturbances develop from roughness elements on the disk and are followed from the linear stage, growing to saturation and finally transitioning to turbulence. Several simulations are presented with varying disturbance amplitudes. The lowest amplitude corresponds approximately to the experiment by Imayama et al. (J. Fluid Mech., vol. 745, 2014a, pp. 132–163). For all cases, the primary instability was found to be convectively unstable, and secondary modes were found to be triggered spontaneously while the flow was developing. The secondary modes further stayed within the domain, and an explanation for this is a proposed globally unstable secondary instability. For the low-amplitude roughness cases, the disturbances propagate beyond the threshold for secondary global instability before becoming turbulent, and for the high-amplitude roughness cases the transition scenario gives a turbulent flow directly at the critical Reynolds number for the secondary global instability. These results correspond to the theory of Pier (J. Engng Maths, vol. 57, 2007, pp. 237–251) predicting a secondary absolute instability. In our simulations, high temporal frequencies were found to grow with a large amplification rate where the secondary global instability occurred. For smaller radial positions, low-frequency secondary instabilities were observed, tripped by the global instability. The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Kármán self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counterclockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m ∈ [32, 78]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M Chomaz, Denis Martinand, Eric Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, 2018, 836, pp.43-71. ⟨10.1017/jfm.2017.771⟩. ⟨hal-02121890⟩
Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien Favier. Rheological properties of synthetic mucus for airway clearance. Journal of Biomedical Materials Research Part A, 2018, 106 (2), pp.386 - 396. ⟨10.1002/jbm.a.36251⟩. ⟨hal-01678912⟩ Plus de détails...
In this work, a complete rheological characterization of bronchial mucus simulants based on the composition proposed by Zahm et al. [1] is presented. Dynamic Small Amplitude Oscillatory Shear (SAOS) experiments, Steady State (SS) flow measurements and three Intervals Thixotropy Tests (3ITT), are carried out to investigate the global rheological complexities of simulants (viscoelasticity, viscoplasticity, shear-thinning and thixotropy) as a function of scleroglucan concentrations (0.5 to 2wt%) and under temperatures of 20 and 37 °C. SAOS measurements show that the limit of the linear viscoelastic range as well as the elasticity both increase with increasing sclerogucan concentrations. Depending on the sollicitation frequency, the 0.5wt% gel response is either liquid-like or solid-like, whereas more concentrated gels show a solid-like response over the whole frequency range. The temperature dependence of gels response is negligible in the 20-37°C range. The Herschel-Bulkley (HB) model is chosen to fit the SS flow curve of simulants. The evolution of HB parameters versus polymer concentration show that both shear-thinning and viscoplasticity increase with increasing concentrations. 3ITTs allow calculation of recovery thixotropic times after shearings at 100s-1 or 1.6s-1. Empiric correlations are proposed to quantify the effect of polymer concentration on rheological parameters of mucus simulants.
Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien Favier. Rheological properties of synthetic mucus for airway clearance. Journal of Biomedical Materials Research Part A, 2018, 106 (2), pp.386 - 396. ⟨10.1002/jbm.a.36251⟩. ⟨hal-01678912⟩
Journal: Journal of Biomedical Materials Research Part A
Eunok Yim, J.-M Chomaz, D Martinand, E Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, 2018. ⟨hal-02927579⟩ Plus de détails...
The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor-stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Kármán self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counterclockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers m, in the range m ∈ [32, 78]. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant-modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.
Eunok Yim, J.-M Chomaz, D Martinand, E Serre. Transition to turbulence in the rotating disk boundary layer of a rotor-stator cavity. Journal of Fluid Mechanics, 2018. ⟨hal-02927579⟩
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga, Eric Serre. A stabilized Powell–Sabin finite-element method for the 2D Euler equations in supersonic regime. Computer Methods in Applied Mechanics and Engineering, 2018, 340, pp.216-235. ⟨10.1016/j.cma.2018.05.032⟩. ⟨hal-01865708⟩ Plus de détails...
In this paper a Powell–Sabin finite-element (PS-FEM) scheme is presented for the solution of the 2D Euler equations in supersonic regime. The spatial discretization is based on PS splines, that are piecewise quadratic polynomials with a global continuity, defined on conforming triangulations. Some geometrical issues related to the practical construction of the PS elements are discussed, in particular, the generation of the control triangles and the imposition of the boundary conditions. A stabilized formulation is considered, and a novel shock-capturing technique in the context of continuous finite-elements is proposed to reduce oscillations around the discontinuity, and compared with the classical technique proposed by Tezduyar and Senga (2006). The code is verified using manufactured solutions and validated using two challenging numerical examples, which allows to evaluate the performance of the PS discretization in capturing the shocks.
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga, Eric Serre. A stabilized Powell–Sabin finite-element method for the 2D Euler equations in supersonic regime. Computer Methods in Applied Mechanics and Engineering, 2018, 340, pp.216-235. ⟨10.1016/j.cma.2018.05.032⟩. ⟨hal-01865708⟩
Journal: Computer Methods in Applied Mechanics and Engineering
Pierre Magnico. Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane. Physics of Fluids, 2018, 30 (1), pp.014101. ⟨10.1063/1.5007930⟩. ⟨hal-02114498⟩ Plus de détails...
This paper is devoted to the numerical investigation of electro-kinetic instability in a polarization layer next to a cation-exchange membrane. An analysis of some properties of the electro-kinetic instability is followed by a detailed description of the fluid flow structure and of the spatial distribution of the ionic flux. In this aim, the Stokes-Poisson-Nernst-Planck equation set is solved until the Debye length scale. The results show that the potential threshold of the marginal instability and the current density depend on the logarithm of the concentration at the membrane surface. The size of the stable vortices seems to be an increasing function of the potential drop. The fluid motion is induced by the electric force along the maximum concentration in the extended space charge (ESC) region and by the pressure force in the region around the inner edge of the ESC layer. Two spots of kinetic energy are located in the ESC region and between the vortices. The cationic motion, controlled by the electric field and the convection, presents counter-rotating vortices in the stagnation zone located in the fluid ejection region. The anion transport is also characterized by two independent layers which contain counter-rotating vortices. The first one is in contact with the stationary reservoir. In the second layer against the membrane, the convection, and the electric field control, the transversal motion, the Fickian diffusion, and the convection are dominant in the longitudinal direction. Finally, the longitudinal disequilibrium of potential and pressure along the membrane is analyzed.
Pierre Magnico. Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane. Physics of Fluids, 2018, 30 (1), pp.014101. ⟨10.1063/1.5007930⟩. ⟨hal-02114498⟩
Thomas Cartier-Michaud, Philippe Ghendrih, Guilhem Dif-Pradalier, Xavier Garbet, Virginie Grandgirard, et al.. Verification of turbulent simulations using PoPe: quantifying model precision and numerical error with data mining of simulation output. Journal of Physics: Conference Series, 2018, 1125, pp.012005. ⟨10.1088/1742-6596/1125/1/012005⟩. ⟨hal-02196674⟩ Plus de détails...
Verification of a 1D-1V kinetic code with the PoPe method [1] is presented. Investigation of the impact of reducing the precision of the numerical scheme is analysed by following 3 indicators of the physics solved by the code, namely the plasma response to an external high frequency electric field wave. The response of the distribution function in the vicinity of the particle-wave resonance is found to be most sensitive to the resolution. Consistently, a rapid growth of the error indicator determined with PoPe is observed. However, no critical value of this indicator allowing us to retain the physics in a situation of degraded precision could be observed. The response of the amplitude of the electric potential fluctuations is characterised by a transient growth followed by a plateau. It is found that the loss of this plateau is governed by the resolution in v-space, but due to the generation of a symmetry in the problem rather than to errors in the numerical scheme. The analysis of the transient indicates that the growth rate of the amplitude of the electric potential is very robust down to very low resolution, step in velocity of 2 thermal velocities. However, a transition prior to this resolution, with step 0.5 thermal velocity, can be identified corresponding to a PoPe indicator of order zero, namely for errors of order 100 %.
Thomas Cartier-Michaud, Philippe Ghendrih, Guilhem Dif-Pradalier, Xavier Garbet, Virginie Grandgirard, et al.. Verification of turbulent simulations using PoPe: quantifying model precision and numerical error with data mining of simulation output. Journal of Physics: Conference Series, 2018, 1125, pp.012005. ⟨10.1088/1742-6596/1125/1/012005⟩. ⟨hal-02196674⟩
T.P. Lyubimova, A.P. Lepikhin, Y.N. Parshakova, C. Gualtieri, S.N. Lane, et al.. Influence of hydrodynamic regimes on mixing of waters of confluent rivers. Computational Continuum Mechanics, 2018, 11 (3), pp.354-361. ⟨10.7242/1999-6691/2018.11.3.26⟩. ⟨hal-02989643⟩ Plus de détails...
Marcello Meldi, Pierre Sagaut. Investigation of anomalous very fast decay regimes in homogeneous isotropic turbulence. Journal of Turbulence, 2018, 19 (5), pp.390 - 413. ⟨10.1080/14685248.2018.1450506⟩. ⟨hal-02114630⟩ Plus de détails...
The emergence of anomalous fast decay regimes in homogeneous isotropic turbulence (HIT) decay is investigated via both theoretical analysis and eddy-damped quasi-normal Markovian simulations. The work provides new insight about a fundamental issue playing a role in HIT decay, namely the influence of non-standard shapes of the energy spectrum, in particular in the large energetic scale region. A detailed analysis of the kinetic energy spectrum E(k) and the non-linear energy transfer T(k) shows that anomalous decay regimes are associated with the relaxation of initial energy spectra which exhibit a bump at energetic scales. This feature induces an increase in the energy cascade rate, toward solutions with a smooth shape at the spectrum peak. Present results match observations reported in wind-tunnel experiments dealing with turbulence decay in the wake of grids and bluff bodies, including scaling laws for the dissipation parameter C-E. They also indicate that the ratio between the initial eddy turnover time and the advection time determines of how fast anomalous regimes relax toward classical turbulence free-decay. This parameter should be used for consistent data comparison and it opens perspectives for the control of multiscale effects in industrial applications.
Marcello Meldi, Pierre Sagaut. Investigation of anomalous very fast decay regimes in homogeneous isotropic turbulence. Journal of Turbulence, 2018, 19 (5), pp.390 - 413. ⟨10.1080/14685248.2018.1450506⟩. ⟨hal-02114630⟩
H. Riahi, Marcello Meldi, Julien Favier, Eric Serre, Eric Goncalves da Silva. A pressure-corrected Immersed Boundary Method for the numerical simulation of compressible flows. Journal of Computational Physics, 2018, 374, pp.361-383. ⟨10.1016/j.jcp.2018.07.033⟩. ⟨hal-01859760⟩ Plus de détails...
The development of an improved new IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows, and it is expanded for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically derived from the set of dynamic equations. The resulting IBM method has been integrated in various flow solvers available in the CFD platform OpenFOAM. A rigorous validation has been performed considering different test cases of increasing complexity. The results have been compared with a large number of references available in the literature of experimental and numerical nature. This analysis highlights numerous favorable characteristics of the IBM method, such as precision, flexibility and computational cost efficiency.
H. Riahi, Marcello Meldi, Julien Favier, Eric Serre, Eric Goncalves da Silva. A pressure-corrected Immersed Boundary Method for the numerical simulation of compressible flows. Journal of Computational Physics, 2018, 374, pp.361-383. ⟨10.1016/j.jcp.2018.07.033⟩. ⟨hal-01859760⟩
Alberto Gallo, Nicolas Fedorczak, Sarah Elmore, Roberto Maurizio, Holger Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, 2018, 60 (1), pp.014007. ⟨10.1088/1361-6587/aa857b⟩. ⟨hal-02114145⟩ Plus de détails...
A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL (${\lambda }_{q}$) and the divertor SOL (S q ). In this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak à Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.
Alberto Gallo, Nicolas Fedorczak, Sarah Elmore, Roberto Maurizio, Holger Reimerdes, et al.. Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X. Plasma Physics and Controlled Fusion, 2018, 60 (1), pp.014007. ⟨10.1088/1361-6587/aa857b⟩. ⟨hal-02114145⟩
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, 2017, pp.1 - 9. ⟨10.1109/JOE.2017.2775978⟩. ⟨hal-01702364⟩ Plus de détails...
Sound-source localization in shallow water is a difficult task due to the complicated environment, e.g., complex sound-speed profile and irregular water bottom reflections. Full-wave numerical techniques are currently able to accurately simulate the propagation of sound waves in such complex environments. However, the source localization problem, which generally involves a large number of sound propagation calculations, still requires a fast computation of the wave equation, and thus a simplified model is well advised. In this paper, a four-layer model is considered, which is able to approximate a wide range of shallow-water environments, particularly those in summer conditions. More specifically, the medium is assumed to be horizontally stratified and vertically divided into four layers, and the sound speed in each layer is assumed to be constant or varying linearly. Under this assumption, the wave propagation can be rapidly computed via a classical wave number integration method. The main contribution of this paper is to show the suitability of the four-layer model in terms of source localization in a complex (range-dependent) environment. The sound-speed profile is assumed to be vertically irregular and horizontally slowly varying and the bottom is nonflat. In the forward problem, sound propagation in complex underwater environments is simulated via a time-domain full-wave simulation approach called the spectral-element method. The source localization error due to model imprecision is analyzed.
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, 2017, pp.1 - 9. ⟨10.1109/JOE.2017.2775978⟩. ⟨hal-01702364⟩
Here, we explain the phenomenon of focusing using the numerical properties of space–time discretization methods involving second-order Adams–Bashforth (AB2) method for the solution of one–dimensional (1D) convection equation. It has been established that solving 1D convection equation by three–time level method invokes a numerical or spurious mode, apart from the physical mode (as explained in Sengupta et al., [27]). Here, the long elusive problem of focusing (considered as a problem of non-linear numerical aspect), is shown due to a linear mechanism. The focusing is shown for a wave–packet propagating in a non-periodic domain by a three–time level method. Long time integration shows the physical mode to cause focusing, which shows up as spectacular growth of error–packet(s) at discrete location(s), where the dominant wavenumber (k) depends only on the CFL number (Nc), for the space–time discretization method. The length scale of growing error is independent of wavenumber of the input signal. It is also established that focusing is related to numerical absolute instability, for which the numerical group velocity (VgN1) of the physical mode is zero. However, interestingly, when a compact filter is used, the focusing phenomenon is converted from absolute to convective numerical instability. This brings new insight and satisfactory explanation of focusing and its dependence on the choice of numerical methods and use of filter. As a demonstration of the focusing phenomenon for AB2 method, we use it with a well known combined compact differencing scheme to solve Navier–Stokes equation in a square lid driven cavity for a super-critical post–Hopf bifurcation Reynolds number of 10,000 (based on the side of the cavity and the constant lid velocity). Contrary to the well-established solution with polygonal vortices in the literature, here the solution breaks down after a finite time due to focusing.
Tapan Sengupta, Pierre Sagaut, Aditi Sengupta, Kumar Saurabh. Global spectral analysis of three-time level integration schemes: Focusing phenomenon. Computers and Fluids, 2017, 157, pp.182 - 195. ⟨10.1016/j.compfluid.2017.08.033⟩. ⟨hal-01702350⟩
Here, we explain the phenomenon of focusing using the numerical properties of space–time discretization methods involving second-order Adams–Bashforth (AB2) method for the solution of one–dimensional (1D) convection equation. It has been established that solving 1D convection equation by three–time level method invokes a numerical or spurious mode, apart from the physical mode (as explained in Sengupta et al., [27]). Here, the long elusive problem of focusing (considered as a problem of non-linear numerical aspect), is shown due to a linear mechanism. The focusing is shown for a wave–packet propagating in a non-periodic domain by a three–time level method. Long time integration shows the physical mode to cause focusing, which shows up as spectacular growth of error–packet(s) at discrete location(s), where the dominant wavenumber (k) depends only on the CFL number (Nc), for the space–time discretization method. The length scale of growing error is independent of wavenumber of the input signal. It is also established that focusing is related to numerical absolute instability, for which the numerical group velocity (VgN1) of the physical mode is zero. However, interestingly, when a compact filter is used, the focusing phenomenon is converted from absolute to convective numerical instability. This brings new insight and satisfactory explanation of focusing and its dependence on the choice of numerical methods and use of filter. As a demonstration of the focusing phenomenon for AB2 method, we use it with a well known combined compact differencing scheme to solve Navier–Stokes equation in a square lid driven cavity for a super-critical post–Hopf bifurcation Reynolds number of 10,000 (based on the side of the cavity and the constant lid velocity). Contrary to the well-established solution with polygonal vortices in the literature, here the solution breaks down after a finite time due to focusing.
Tapan Sengupta, Pierre Sagaut, Aditi Sengupta, Kumar Saurabh. Global spectral analysis of three-time level integration schemes: Focusing phenomenon. Computers and Fluids, 2017, 157, pp.182 - 195. ⟨10.1016/j.compfluid.2017.08.033⟩. ⟨hal-01702350⟩
A novel implicit immersed boundary method of high accuracy and efficiency is presented for the simulation of incompressible viscous flow over complex stationary or moving solid boundaries. A boundary force is often introduced in many immersed boundary methods to mimic the presence of solid boundary, such that the overall simulation can be performed on a simple Cartesian grid. The current method inherits this idea and considers the boundary force as a Lagrange multiplier to enforce the no-slip constraint at the solid boundary, instead of applying constitutional relations for rigid bodies. Hence excessive constraint on the time step is circumvented, and the time step only depends on the discretization of fluid Navier-Stokes equations, like the CFL condition in present work. To determine the boundary force, an additional moving force equation is derived. The dimension of this derived system is proportional to the number of Lagrangian points describing the solid boundaries, which makes the method very suitable for moving boundary problems since the time for matrix update and system solving is not significant. The force coefficient matrix is made symmetric and positive definite so that the conjugate gradient method can solve the system quickly. The proposed immersed boundary method is incorporated into the fluid solver with a second-order accurate projection method as a plug-in. The overall scheme is handled under an efficient fractional step framework, namely, prediction, forcing, and projection. Various simulations are performed to validate current method, and the results compare well with previous experimental and numerical studies.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Moving immersed boundary method. International Journal for Numerical Methods in Fluids, 2017, 85 (5), pp.288 - 323. ⟨10.1002/fld.4382⟩. ⟨hal-01592822⟩
Journal: International Journal for Numerical Methods in Fluids
V. Mons, Luca Margheri, J.-C. Chassaing, Pierre Sagaut. Data assimilation-based reconstruction of urban pollutant release characteristics. Journal of Wind Engineering and Industrial Aerodynamics, 2017, 169, pp.232 - 250. ⟨10.1016/j.jweia.2017.07.007⟩. ⟨hal-01631036⟩ Plus de détails...
V. Mons, Luca Margheri, J.-C. Chassaing, Pierre Sagaut. Data assimilation-based reconstruction of urban pollutant release characteristics. Journal of Wind Engineering and Industrial Aerodynamics, 2017, 169, pp.232 - 250. ⟨10.1016/j.jweia.2017.07.007⟩. ⟨hal-01631036⟩
Journal: Journal of Wind Engineering and Industrial Aerodynamics
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, 2017, 826, pp.503 - 521. ⟨10.1017/jfm.2017.439⟩. ⟨hal-01585331⟩ Plus de détails...
The flow over an open cavity is an example of supercritical Hopf bifurcation leading to periodic limit-cycle oscillations. One of its distinctive features is the existence of strong higher harmonics, which results in the time-averaged mean flow being strongly linearly unstable. For this class of flows, a simplified formalism capable of unravelling how exactly the instability grows and saturates is lacking. This study builds on previous work by Mantic-Lugo et al. (Phys. Rev. Lett., vol. 113, 2014, 084501) to fill in the gap using a parametrized approximation of an instantaneous, phase-averaged mean flow, coupled in a quasi-static manner to multiple linear harmonic disturbances interacting nonlinearly with one another and feeding back on the mean flow via their Reynolds stresses. This provides a self-consistent modelling of the mean flow-fluctuation interaction, in the sense that all perturbation structures are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations. The first harmonic is sought as the superposition of two components, a linear component generated by the instability and aligned along the leading eigenmode of the mean flow, and a nonlinear orthogonal component generated by the higher harmonics, which progressively distorts the linear growth rate and eigenfrequency of the eigenmode. Saturation occurs when the growth rate of the first harmonic is zero, at which point the stabilizing effect of the second harmonic balances exactly the linear instability of the eigenmode. The model does not require any input from numerical or experimental data, and accurately predicts the transient development and the saturation of the instability, as established from comparison to time and phase averages of direct numerical simulation data.
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, 2017, 826, pp.503 - 521. ⟨10.1017/jfm.2017.439⟩. ⟨hal-01585331⟩
A lattice Boltzmann method (LBM) with enhanced stability and accuracy is presented for various Hermite tensor-based lattice structures. The collision operator relies on a regularization step, which is here improved through a recursive computation of nonequilibrium Hermite polynomial coefficients. In addition to the reduced computational cost of this procedure with respect to the standard one, the recursive step allows to considerably enhance the stability and accuracy of the numerical scheme by properly filtering out second-(and higher-) order nonhydrodynamic contributions in under-resolved conditions. This is first shown in the isothermal case where the simulation of the doubly periodic shear layer is performed with a Reynolds number ranging from 104 to 10(6), and where a thorough analysis of the case at Re = 3 x 10(4) is conducted. In the latter, results obtained using both regularization steps are compared against the Bhatnagar-Gross-Krook LBM for standard (D2Q9) and high-order (D2V17 and D2V37) lattice structures, confirming the tremendous increase of stability range of the proposed approach. Further comparisons on thermal and fully compressible flows, using the general extension of this procedure, are then conducted through the numerical simulation of Sod shock tubes with the D2V37 lattice. They confirm the stability increase induced by the recursive approach as compared with the standard one.
Christophe Coreixas, Gauthier Wissocq, Guillaume Puigt, Jean-François Boussuge, Pierre Sagaut. Recursive regularization step for high-order lattice Boltzmann methods. Physical Review E , 2017, 96 (3), pp.033306. ⟨10.1103/PhysRevE.96.033306⟩. ⟨hal-01596322⟩
Olivier Lafforgue, N. Bouguerra, Sebastien Poncet, Isabelle Seyssiecq, Julien Favier, et al.. Thermo-physical properties of synthetic mucus for the study of airway clearance. Journal of Biomedical Materials Research Part A, 2017, 105 (11), pp.3025-3033 ⟨10.1002/jbm.a.36161⟩. ⟨hal-01596484⟩ Plus de détails...
In this article, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al., Eur Respir J 1991; 4: 311–315 were experiementally determined. This simulant is mainly composed of a galactomannan gum and a scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of scleroglucan concentrations. More importantly and for some scleroglucan concentrations, the syntetic mucus, exhibits, somehow, comparable thermophysical properties to real bronchial mucus. An insight on the microstructure of this simulant is proposed and the different properties enounced previously have been measured for various scleroglucan concentrations and over a certain range of operating temperatures. This synthetic mucus is found to mimic well the rheological behavior and the surface tension of real mucus for different pathologies. Density and thermal properties have been measured for the first time.
Olivier Lafforgue, N. Bouguerra, Sebastien Poncet, Isabelle Seyssiecq, Julien Favier, et al.. Thermo-physical properties of synthetic mucus for the study of airway clearance. Journal of Biomedical Materials Research Part A, 2017, 105 (11), pp.3025-3033 ⟨10.1002/jbm.a.36161⟩. ⟨hal-01596484⟩
Journal: Journal of Biomedical Materials Research Part A
Sylvain Chateau, Julien Favier, Umberto D’ortona, Sebastien Poncet. Transport efficiency of metachronal waves in 3D cilium arrays immersed in a two-phase flow. Journal of Fluid Mechanics, 2017, 824, pp.931 - 961. ⟨10.1017/jfm.2017.352⟩. ⟨hal-01592834⟩ Plus de détails...
This work reports the formation and characterization of antipleptic and symplectic metachronal waves in 3D cilium arrays immersed in a two-fluid environment, with a viscosity ratio of 20. A coupled lattice Boltzmann-immersed-boundary solver is used. The periciliary layer is confined between the epithelial surface and the mucus. Its thickness is chosen such that the tips of the cilia can penetrate the mucus. A purely hydrodynamical feedback of the fluid is taken into account and a coupling parameter alpha is introduced, which allows tuning of both the direction of the wave propagation and the strength of the fluid feedback. A comparative study of both antipleptic and symplectic waves, mapping a cilium interspacing ranging from 1.67 up to 5 cilium lengths, is performed by imposing metachrony. Antipleptic waves are found to systematically outperform symplectic waves. They are shown to be more efficient for transporting and mixing the fluids, while spending less energy than symplectic, random or synchronized motions.
Sylvain Chateau, Julien Favier, Umberto D’ortona, Sebastien Poncet. Transport efficiency of metachronal waves in 3D cilium arrays immersed in a two-phase flow. Journal of Fluid Mechanics, 2017, 824, pp.931 - 961. ⟨10.1017/jfm.2017.352⟩. ⟨hal-01592834⟩
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, 2017, 824, pp.438 - 476. ⟨10.1017/jfm.2017.351⟩. ⟨hal-01592948⟩ Plus de détails...
Extending previous linear stability analyses of the instabilities developing in permeable Taylor-Couette-Poiseuille flows where axial and radial throughflows are superimposed on the usual Taylor-Couette flow, we further examine the linear behaviour and expand the analysis to consider the weakly nonlinear behaviour of convective-type instabilities by means of the derivation of the fifth-order amplitude equation together with direct numerical simulations. Special attention is paid to the influence of the radius ratio eta = r(in)/r(out), and particularly to wide gaps (small eta) and how they magnify the effects of the radial flow. The instabilities take the form of pairs of counter-rotating toroidal vortices superseded by helical ones as the axial flow is increased. Increasing the radial inflow draws these vortices near the inner cylinder, where they shrink relative to the annular gap, when this gap is wide. Strong axial and radial flows in a narrow annular gap lead to a very large azimuthal wavenumber with steeply sloped helical vortices. Strong radial outflow in a wide annular gap results in very large helical vortices. The analytical and numerical saturated vortices match quite well. In addition, radial inflows or outflows can turn the usually supercritical bifurcation from laminar to vortical flow into a subcritical one. The radial flow above which this change occurs decreases as the radius ratio eta decreases. A practical motivation for this weakly nonlinear analysis is found in modelling dynamic filtration devices, which rely on vortical instabilities to reduce the processes of accumulation on their membranes.
Denis Martinand, Eric Serre, Richard M. Lueptow. Linear and weakly nonlinear analyses of cylindrical Couette flow with axial and radial flows. Journal of Fluid Mechanics, 2017, 824, pp.438 - 476. ⟨10.1017/jfm.2017.351⟩. ⟨hal-01592948⟩
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, 2017, 12, pp.187 - 192. ⟨10.1016/j.nme.2016.12.025⟩. ⟨hal-01702237⟩ Plus de détails...
Simulations of WEST H-mode divertor scenarios have been performed with SOLEDGE2D-EIRENE edge plasma transport code, both for pure deuterium and nitrogen seeded discharge. In the pure deuterium case, a target heat flux of 8 MW/m2 is reached, but misalignment between heat and the particle outflux yields 50 eV plasma temperature at the target plates. With nitrogen seeding, the heat and particle outflux are observed to be aligned so that lower plasma temperatures at the target plates are achieved together with the required high heat fluxes. This change in heat and particle outflux alignment is analysed with respect to the role of divertor geometry and the impact of vertical vs horizontal target plates on neutrals spreading.
G. Ciraolo, H. Bufferand, J. Bucalossi, Ph. Ghendrih, P. Tamain, et al.. H-mode WEST tungsten divertor operation: deuterium and nitrogen seeded simulations with SOLEDGE2D-EIRENE. Nuclear Materials and Energy, 2017, 12, pp.187 - 192. ⟨10.1016/j.nme.2016.12.025⟩. ⟨hal-01702237⟩
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, 2017, 157, pp.55 - 72. ⟨10.1016/j.compfluid.2017.08.001⟩. ⟨hal-01591562⟩ Plus de détails...
The present work proposes a modified Pressure-Implicit Split-Operator (PISO) solver integrating the recent Immersed Boundary Method (IBM) proposed by Pinelli et al. [1] in order to perform reliable simulations of incompressible flows around bluff bodies using the open source toolbox OpenFOAM version 2.2 (ESI-OpenCFD [2]). The (IBM) allows for a precise representation of fixed and moving solid obstacles embedded in the physical domain, using uniform or stretched Cartesian meshes. Owing to this feature, the maximum level of accuracy and scalability of the numerical solvers can be systematically achieved. An iterative scheme based on sub-iterations between (IBM) and pressure correction has been implemented in the native (PISO) solver of OpenFOAM. This allows one to use fast optimized Poisson solvers while satisfying simultaneously the divergence-free flow state and the no-slip condition at the body surface. To compute the divergence of the momentum equation (in the PISO loop) and the interpolation of the fluxes, we propose an hybrid calculation with an analytical resolution (using the kernel function equation) of the quantities involving the force term (singular quantities). A careful and original verification study has been carried out which allows to estimate three different errors related to the discretization and to the (IBM). Various 2D and 3D well-documented test cases of academic flows around fixed or moving cylinders have been simulated and carefully validated against existing data from the literature in a large range of Reynolds numbers, Re = 30 − 3900 and in the frame of DNS and DDES OpenFOAM native models.
Eddy Constant, Julien Favier, Marcello Meldi, Philippe Meliga, Eric Serre. An immersed boundary method in OpenFOAM : Verification and validation. Computers and Fluids, 2017, 157, pp.55 - 72. ⟨10.1016/j.compfluid.2017.08.001⟩. ⟨hal-01591562⟩
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, 2017, 12, pp.1171 - 1177. ⟨10.1016/j.nme.2016.12.022⟩. ⟨hal-01702267⟩ Plus de détails...
Motivated by Radio Frequency (RF) heating studies, the response of the plasma of tokamaks to the presence of a locally polarized limiter is studied. In a first part, we use the TOKAM3X 3D global edge turbulence code to analyse the impact of such biasing in a realistic geometry. Key features of experimental observations are qualitatively recovered, especially the extension of a potential and density perturbation on long, but finite, distances along connected field lines. The perturbation is also found to extend in the transverse direction. Both observations demonstrate the influence of perpendicular current loops on the plasma confirming the need for an accurate description in reduced models. In a second part, we use the TOKAM2D slab turbulence code to determine the validity of using a transverse Ohm's law for this purpose. Results indicate that a local Ohm's law with a constant and uniform perpendicular resistivity appears at least as an oversimplified description of perpendicular charge transport in a turbulent Scrape-Off Layer.
P. Tamain, C. Colin, L. Colas, C. Baudoin, G. Ciraolo, et al.. Numerical analysis of the impact of an RF sheath on the Scrape-Off Layer in 2D and 3D turbulence simulations. Nuclear Materials and Energy, 2017, 12, pp.1171 - 1177. ⟨10.1016/j.nme.2016.12.022⟩. ⟨hal-01702267⟩
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, 2017, 12, pp.953 - 958. ⟨10.1016/j.nme.2017.01.008⟩. ⟨hal-01702255⟩ Plus de détails...
The flux expansion effect on the Scrape-Off Layer equilibrium is inspected through TOKAM3X 3D turbulence simulations. Three magnetic equilibria with analytically controlled flux expansion are built, representing respectively a positive, a null and a negative Shafranov shift. Turbulent E × B fluxes across flux surfaces show similar amplitudes and poloidal distributions in all cases. The ballooning nature of the interchange instability is recovered, with an enhancement of turbulence in the vicinity of the limiter, probably due to a Kelvin–Helmoltz instability. Interestingly, the poloidally averaged density decay length is found to be shorter almost by a factor 2 in the case of flux surfaces compressed at the low-field side midplane, with respect to the opposite case, indicating the presence of unfavorable conditions for the turbulent transport. The difference in the magnetic field line shape is pointed out as a mechanism which affects the turbulent transport across the flux surfaces. Indeed the unstable region has a larger parallel extension when flux expansion in the low-field side is larger. Moreover, the configuration with a lower magnetic shear at the low-field side midplane shows a more unstable behavior. The role of this parameter in turbulence stabilization is qualitatively evaluated. The difference in the distribution of transport along the parallel direction is shown to affect also the parallel flows, which are analyzed for the three proposed cases.
Davide Galassi, P. Tamain, C. Baudoin, H. Bufferand, G. Ciraolo, et al.. Flux expansion effect on turbulent transport in 3D global simulations. Nuclear Materials and Energy, 2017, 12, pp.953 - 958. ⟨10.1016/j.nme.2017.01.008⟩. ⟨hal-01702255⟩
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, 2017, 12, pp.798 - 807. ⟨10.1016/j.nme.2017.02.022⟩. ⟨hal-01702187⟩ Plus de détails...
Seeded filament simulations are used to study blob dynamics with the state-of-the-art TOKAM3X fluid code in the scrape-off layer (SOL) using a slab geometry. The filamentary dynamics recovered with the code are compared with previously predicted analytical blob velocity scalings while also studying the effect of field line pitch angle on these dynamics and are found to be similar. The effect of changing magnetic topology on filamentary motion is also investigated. Magnetic shear is introduced in the model by the sudden and localised variation of field line pitch angle for a narrow radially located region constituting effectively a shearing zone. Three such shear zones are tested to see how they affect filament motion. Filaments are initialised radially upstream from the shear zone and recorded as they convect towards the far-SOL side. The lowest intensity shear zone allows many of the higher amplitude filaments to pass through after dampening them. On the other hand, the highest intensity shear zones prevent all filaments from progressing to the wall beyond the shear zone and, in certain cases for high density amplitude filaments, is able to generate a new filament downstream from the shear zone.
W.A. Gracias, P. Tamain, Eric Serre, R.A. Pitts, L. Garcia. The impact of magnetic shear on the dynamics of a seeded 3D filament in slab geometry. Nuclear Materials and Energy, 2017, 12, pp.798 - 807. ⟨10.1016/j.nme.2017.02.022⟩. ⟨hal-01702187⟩
Félix Gendre, Denis Ricot, Guillaume Fritz, Pierre Sagaut. Grid refinement for aeroacoustics in the lattice Boltzmann method: A directional splitting approach. Physical Review E , 2017, 96 (2), pp.023311. ⟨10.1103/PhysRevE.96.023311⟩. ⟨hal-04348563⟩ Plus de détails...
This study focuses on grid refinement techniques for the direct simulation of aeroacoustics, when using weakly compressible lattice Boltzmann models, such as the D3Q19 athermal velocity set. When it comes to direct noise computation, very small errors on the density or pressure field may have great negative consequences. Even strong acoustic density fluctuations have indeed a clearly lower amplitude than the hydrodynamic ones. This work deals with such very weak spurious fluctuations that emerge when a vortical structure crosses a refinement interface, which may contaminate the resulting aeroacoustic field. We show through an extensive literature review that, within the framework described above, this issue has never been addressed before. To tackle this problem, we develop an alternative algorithm and compare its behavior to a classical one, which fits our in-house vertex-centered data structure. Our main idea relies on a directional splitting of the continuous discrete velocity Boltzmann equation, followed by an integration over specific characteristics. This method can be seen as a specific coupling between finite difference and lattice Boltzmann, locally on the interface between the two grids. The method is assessed considering two cases: an acoustic pulse and a convected vortex. We show how very small errors on the density field arise and propagate throughout the domain when a vortical flow crosses the refinement interface. We also show that an increased free stream Mach number (but still within the weakly compressible regime) strongly deteriorates the situation, although the magnitude of the errors may remain negligible for purely aerodynamic studies. A drastically reduced level of error for the near-field spurious noise is obtained with our approach, especially for under-resolved simulations, a situation that is crucial for industrial applications. Thus, the vortex case is proved useful for aeroacoustic validations of any grid refinement algorithm.
Félix Gendre, Denis Ricot, Guillaume Fritz, Pierre Sagaut. Grid refinement for aeroacoustics in the lattice Boltzmann method: A directional splitting approach. Physical Review E , 2017, 96 (2), pp.023311. ⟨10.1103/PhysRevE.96.023311⟩. ⟨hal-04348563⟩
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, 2017, 12, pp.931 - 934. ⟨10.1016/j.nme.2017.02.007⟩. ⟨hal-01702229⟩ Plus de détails...
Transport codes are the main workhorses for global edge studies and modern divertor design. These tools do not resolve turbulent fluctuations responsible for the bulk of cross-field transport in the Scrape-off Layer (SOL), and solve mean field equations instead. Turbulent fluxes are modelled by diffusive transport along the gradients of the mean fields. Improvements of this description, on the basis of approaches developed in computational fluid dynamics are discussed, broadening the outlook given in Bufferand et al. (2016) [10]. This contribution focuses on additional closure issues related to non-linearities in sources/sinks from plasma-wall interactions, here sputtered fluxes from the plasma facing components. “Fluctuation dressed” sputtering yields Yeff are introduced and calculated from turbulence simulations. Properly taking fluctuations into account is shown to lead to higher sputtering at sub-threshold energies compared to mean field predictions. As a first step towards an implementation in a transport code, the possibility of parametrizing Yeff in terms of the mean fields is tentatively investigated.
Y. Marandet, H. Bufferand, N. Nace, M. Valentinuzzi, G. Ciraolo, et al.. Towards a consistent modelling of plasma edge turbulence in mean field transport codes: Focus on sputtering and plasma fluctuations. Nuclear Materials and Energy, 2017, 12, pp.931 - 934. ⟨10.1016/j.nme.2017.02.007⟩. ⟨hal-01702229⟩
Vincent Mons, Jean-Camille Chassaing, Pierre Sagaut. Optimal sensor placement for variational data assimilation of unsteady flows past a rotationally oscillating cylinder. Journal of Fluid Mechanics, 2017, 823, pp.230 - 277. ⟨10.1017/jfm.2017.313⟩. ⟨hal-01548417⟩ Plus de détails...
Vincent Mons, Jean-Camille Chassaing, Pierre Sagaut. Optimal sensor placement for variational data assimilation of unsteady flows past a rotationally oscillating cylinder. Journal of Fluid Mechanics, 2017, 823, pp.230 - 277. ⟨10.1017/jfm.2017.313⟩. ⟨hal-01548417⟩
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, 2017, 2 (7), pp.073905. ⟨10.1103/PhysRevFluids.2.073905⟩. ⟨hal-01698605⟩ Plus de détails...
We provide in-depth scrutiny of two methods making use of adjoint-based gradients to compute the sensitivity of drag in the two-dimensional, periodic flow past a circular cylinder (Re≲189): first, the time-stepping analysis used in Meliga et al. [Phys. Fluids 26, 104101 (2014)] that relies on classical Navier-Stokes modeling and determines the sensitivity to any generic control force from time-dependent adjoint equations marched backwards in time; and, second, a self-consistent approach building on the model of Mantič-Lugo et al. [Phys. Rev. Lett. 113, 084501 (2014)] to compute semilinear approximations of the sensitivity to the mean and fluctuating components of the force. Both approaches are applied to open-loop control by a small secondary cylinder and allow identifying the sensitive regions without knowledge of the controlled states. The theoretical predictions obtained by time-stepping analysis reproduce well the results obtained by direct numerical simulation of the two-cylinder system. So do the predictions obtained by self-consistent analysis, which corroborates the relevance of the approach as a guideline for efficient and systematic control design in the attempt to reduce drag, even though the Reynolds number is not close to the instability threshold and the oscillation amplitude is not small. This is because, unlike simpler approaches relying on linear stability analysis to predict the main features of the flow unsteadiness, the semilinear framework encompasses rigorously the effect of the control on the mean flow, as well as on the finite-amplitude fluctuation that feeds back nonlinearly onto the mean flow via the formation of Reynolds stresses. Such results are especially promising as the self-consistent approach determines the sensitivity from time-independent equations that can be solved iteratively, which makes it generally less computationally demanding. We ultimately discuss the extent to which relevant information can be gained from a hybrid modeling computing self-consistent sensitivities from the postprocessing of DNS data. Application to alternative control objectives such as increasing the lift and alleviating the fluctuating drag and lift is also discussed.
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, 2017, 2 (7), pp.073905. ⟨10.1103/PhysRevFluids.2.073905⟩. ⟨hal-01698605⟩
Congshan Zhuo, Pierre Sagaut. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit. Physical Review E , 2017, 95 (6), pp.063301. ⟨10.1103/PhysRevE.95.063301⟩. ⟨hal-01548424⟩ Plus de détails...
Congshan Zhuo, Pierre Sagaut. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit. Physical Review E , 2017, 95 (6), pp.063301. ⟨10.1103/PhysRevE.95.063301⟩. ⟨hal-01548424⟩
Alistair Revell, Joseph O’connor, Abhishek Sarkar, Cuicui Li, Julien Favier, et al.. The PELskin project: part II—investigating the physical coupling between flexible filaments in an oscillating flow. Meccanica, 2017, 52 (8), pp.1781 - 1795. ⟨10.1007/s11012-016-0525-9⟩. ⟨hal-01592870⟩ Plus de détails...
The fluid-structure interaction mechanisms of a coating composed of flexible flaps immersed in a periodically oscillating channel flow is here studied by means of numerical simulation, employing the Euler-Bernoulli equations to account for the flexibility of the structures. A set of passively actuated flaps have previously been demonstrated to deliver favourable aerodynamic impact when attached to a bluff body undergoing periodic vortex shedding. As such, the present configuration is identified to provide a useful test-bed to better understand this mechanism, thought to be linked to experimentally observed travelling waves. Having previously validated and elucidated the flow mechanism in Paper 1 of this series, we hereby undertake a more detailed analysis of spectra obtained for different natural frequency of structures and different configurations, in order to better characterize the mechanisms involved in the organized motion of the structures. Herein, this wave-like behaviour, observed at the tips of flexible structures via interaction with the fluid flow, is characterized by examining the time history of the filaments motion and the corresponding effects on the fluid flow, in terms of dynamics and frequency of the fluid velocity. Results indicate that the wave motion behaviour is associated with the formation of vortices in the gaps between the flaps, which itself are a function of the structural resistance to the cross flow. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case.
Alistair Revell, Joseph O’connor, Abhishek Sarkar, Cuicui Li, Julien Favier, et al.. The PELskin project: part II—investigating the physical coupling between flexible filaments in an oscillating flow. Meccanica, 2017, 52 (8), pp.1781 - 1795. ⟨10.1007/s11012-016-0525-9⟩. ⟨hal-01592870⟩
Julien Favier, Cuicui Li, Laura Kamps, Alistair Revell, Joseph O’connor, et al.. The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow. Meccanica, 2017, 52 (8), pp.1767 - 1780. ⟨10.1007/s11012-016-0521-0⟩. ⟨hal-01592866⟩ Plus de détails...
Previous studies of flexible flaps attached to the aft part of a cylinder have demonstrated a favourable effect on the drag and lift force fluctuation. This observation is thought to be linked to the excitation of travelling waves along the flaps and as a consequence of that, periodic shedding of the von Karman vortices is altered in phase. A more general case of such interaction is studied herein for a limited row of flaps in an oscillating flow; representative of the cylinder case since the transversal flow in the wake-region shows oscillating character. This reference case is chosen to qualify recently developed numerical methods for the simulation of fluid-structure interaction in the context of the EU funded 'PELskin' project. The simulation of the two-way coupled dynamics of the flexible elements is achieved via a structure model for the flap motion, which was implemented and coupled to two different fluid solvers via the immersed boundary method. The results show the waving behaviour observed at the tips of the flexible elements in interaction with the fluid flow and the formation of vortices in the gaps between the flaps. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case.
Julien Favier, Cuicui Li, Laura Kamps, Alistair Revell, Joseph O’connor, et al.. The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow. Meccanica, 2017, 52 (8), pp.1767 - 1780. ⟨10.1007/s11012-016-0521-0⟩. ⟨hal-01592866⟩
Alekseenko Elena, Bernard Roux. Submerged Aquatic Vegetation Restoration in Brackish Ecosystems Subject to Strong Winds and Coastal Jets. Oceanography & Fisheries Open access Journal, 2017, 2 (4), pp.555595. ⟨10.19080/OFOAJ.2017.02.555595⟩. ⟨hal-01813859⟩ Plus de détails...
The bottom shear stress (BSS) in a windy Mediterranean lagoon has been carefully investigated through numerical modelling. BSS maps have been obtained for the entire lagoon. The aim is to compare BSS with its critical value in the near shoreareas selected for SAV replanting which are subject to downwind coastal jets.
Alekseenko Elena, Bernard Roux. Submerged Aquatic Vegetation Restoration in Brackish Ecosystems Subject to Strong Winds and Coastal Jets. Oceanography & Fisheries Open access Journal, 2017, 2 (4), pp.555595. ⟨10.19080/OFOAJ.2017.02.555595⟩. ⟨hal-01813859⟩
Journal: Oceanography & Fisheries Open access Journal
Marcello Meldi, Pierre Sagaut. Turbulence in a box: quantification of large-scale resolution effects in isotropic turbulence free decay. Journal of Fluid Mechanics, 2017, 818, pp.697 - 715. ⟨10.1017/jfm.2017.158⟩. ⟨hal-01527613⟩ Plus de détails...
The effects of the finiteness of the physical domain over the free decay of homogeneous isotropic turbulence are explored in the present article. Saturation at the large scales is investigated by the use of theoretical analysis and eddy-damped quasi-normal Markovian calculations. Both analyses indicate a strong sensitivity of the large-scale features of the flow to saturation and finite Reynolds number effects. This aspect plays an important role in the general lack of agreement between grid turbulence experiments and numerical simulations. On the other hand, the statistical quantities associated with the behaviour of the spectrum in the inertial region are only marginally affected by saturation. These results suggest new guidelines for the interpretation of experimental and direct numerical simulation studies.
Marcello Meldi, Pierre Sagaut. Turbulence in a box: quantification of large-scale resolution effects in isotropic turbulence free decay. Journal of Fluid Mechanics, 2017, 818, pp.697 - 715. ⟨10.1017/jfm.2017.158⟩. ⟨hal-01527613⟩
Xun Wang, Shahram Khazaie, Luca Margheri, Pierre Sagaut. Shallow water sound source localization using the iterative beamforming method in an image framework. Journal of Sound and Vibration, 2017, 395, pp.354 - 370. ⟨10.1016/j.jsv.2017.02.032⟩. ⟨hal-01527615⟩ Plus de détails...
Shallow water is a complicated sound propagation medium due to multiple reflections by water surface and bottom, imprecisely measured sound speed, noisy environment, etc. Therefore, in order to localize a shallow water sound source, classical signal processing techniques must be improved by taking these complexities into account. In this work, the multiple reflections and uncertain reflectivity of water bottom are explicitly modeled. In the proposed model, a measured signal is a mixture of the direct propagation from the source and the multiple reflections. Instead of solving the Helmholtz equation with boundary conditions of reflections, each signal is interpreted as a superposition of signals emitting from the physical source and its image sources in a free space, which results in a fast computation of sound propagation. Then, the source location, along with its amplitude, reflection paths and power loss of bottom reflection, is estimated via the iterative beamforming (IB) method, which alternatively estimates the source contributions and performs beamforming on these estimates until convergence. This approach does not need to compute the sound propagation for all the possible source locations in a large space, which thus leads to a low computational cost. Finally, numerical simulations are introduced to illustrate the advantage of the proposed model and the source estimation method. The sensitivity of the proposed method with respect to model parameter uncertainties is also investigated via a full uncertainty quantification analysis. The localization error of IB is proved to be acceptable in the given error range of sound speed and water depth. Besides, the IB source estimate is more sensitive to the sound speed while the matched-field processing methods have a stronger sensitivity to the water depth: this result can guide the choice of source localization method in different cases of model parameter uncertainties.
Xun Wang, Shahram Khazaie, Luca Margheri, Pierre Sagaut. Shallow water sound source localization using the iterative beamforming method in an image framework. Journal of Sound and Vibration, 2017, 395, pp.354 - 370. ⟨10.1016/j.jsv.2017.02.032⟩. ⟨hal-01527615⟩
The spectral analysis is a basic tool to characterise the behaviour of any convection scheme. By nature, the solution projected onto the Fourier basis enables to estimate the dissipation and the dispersion associated with the spatial discretisation of the hyperbolic linear problem. In this paper, we wish to revisit such analysis, focusing attention on two key points. The first point concerns the effects of time integration on the spectral analysis. It is shown with standard high-order Finite Difference schemes dedicated to aeroacoustics that the time integration has an effect on the required number of points per wavelength. The situation depends on the choice of the coupled schemes (one for time integration, one for space derivative and one for the filter) and here, the compact scheme with its eighth-order filter seems to have a better spectral accuracy than the considered dispersion relation preserving scheme with its associated filter, especially in terms of dissipation. Secondly, such a coupled space time approach is applied to the new class of high-order spectral discontinuous approaches, focusing especially on the Spectral Difference method. A new way to address the specific spectral behaviour of the scheme is introduced first for wavenumbers in [0,pi], following the Matrix Power method. For wavenumbers above pi, an aliasing phenomenon always occurs but it is possible to understand and to control the aliasing of the signal. It is shown that aliasing depends on the polynomial degree and on the number of time steps. A new way to define dissipation and dispersion is introduced and applied to wavenumbers larger than it. Since the new criteria recover the previous results for wavenumbers below it, the new proposed approach is an extension of all the previous ones dealing with dissipation and dispersion errors. At last, since the standard Finite Difference schemes can serve as reference solution for their capability in aeroacoustics, it is shown that the Spectral Difference method is as accurate as (or even more accurate) than the considered Finite Difference schemes.
Julien Vanharen, Guillaume Puigt, Xavier Vasseur, Jean-François Boussuge, Pierre Sagaut. Revisiting the spectral analysis for high-order spectral discontinuous methods. Journal of Computational Physics, 2017, 337, pp.379 - 402. ⟨10.1016/j.jcp.2017.02.043⟩. ⟨hal-01527618⟩
Yosuke Anzai, Koji Fukagata, Philippe Meliga, Edouard Boujo, François Gallaire. Numerical simulation and sensitivity analysis of a low-Reynolds-number flow around a square cylinder controlled using plasma actuators. Physical Review Fluids, 2017, 2 (4), ⟨10.1103/PhysRevFluids.2.043901⟩. ⟨hal-01585359⟩ Plus de détails...
Flow around a square cylinder controlled using plasma actuators (PAs) is numerically investigated by direct numerical simulation in order to clarify the most effective location of actuator installation and to elucidate the mechanism of control effect. The Reynolds number based on the cylinder diameter and the free-stream velocity is set to be 100 to study the fundamental effect of PAs on two-dimensional vortex shedding, and three different locations of PAs are considered. The mean drag and the root-mean-square of lift fluctuations are found to be reduced by 51% and 99% in the case where two opposing PAs are aligned vertically on the rear surface. In that case, a jet flow similar to a base jet is generated by the collision of the streaming flows induced by the two opposing PAs, and the vortex shedding is completely suppressed. The simulation results are ultimately revisited in the frame of linear sensitivity analysis, whose computational cost is much lower than that of performing the full simulation. A good agreement is reported for low control amplitudes, which allows further discussion of the linear optimal arrangement for any number of PAs.
Yosuke Anzai, Koji Fukagata, Philippe Meliga, Edouard Boujo, François Gallaire. Numerical simulation and sensitivity analysis of a low-Reynolds-number flow around a square cylinder controlled using plasma actuators. Physical Review Fluids, 2017, 2 (4), ⟨10.1103/PhysRevFluids.2.043901⟩. ⟨hal-01585359⟩
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, 2017, 57 (3), pp.036029. ⟨10.1088/1741-4326/aa5332⟩. ⟨hal-01592945⟩ Plus de détails...
The poloidal asymmetries of parallel flows in edge plasmas are investigated by the 3D fluid turbulence code TOKAM3X. A diverted COMPASS-like magnetic equilibrium is used for the simulations. The measurements and simulations of parallel Mach numbers are compared, and exhibit good qualitative agreement. Small-scale turbulent transport is observed to dominate near the low field side midplane, even though it co-exists with significant large-scale cross-field fluxes. Despite the turbulent nature of the plasma in the divertor region, simulations show the low effectiveness of turbulence for the cross-field transport towards the private flux region. Nevertheless, a complex pattern of fluxes associated with the average field components are found to cross the separatrix in the divertor region. Large-scale and small-scale turbulent E x B transport, along with the del B drift, drive the asymmetries in parallel flows. A semian-alytical model based on mass and parallel momentum balances allows the poloidal drift effects on the asymmetry pattern to be evaluated. As in the experiments, a reversed B-T simulation provides a way of self-consistently separating the effects of turbulent transport and large-scale flows, which must be reversed for a reversed field. The large-scale contribution is found to be responsible for typically 50% of the effect on the Mach number, evaluated at the top of the machine. The presented picture shows the complex interplay between drifts and turbulence, underlining the necessity of a global approach to edge plasma modelling, including a self-consistent description of the turbulence.
Davide Galassi, P. Tamain, H. Bufferand, Guido Ciraolo, Ph. Ghendrih, et al.. Drive of parallel flows by turbulence and large-scale E × B transverse transport in divertor geometry. Nuclear Fusion, 2017, 57 (3), pp.036029. ⟨10.1088/1741-4326/aa5332⟩. ⟨hal-01592945⟩
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, 2017, 63, pp.119 - 127. ⟨10.1016/j.ijheatfluidflow.2016.09.011⟩. ⟨hal-01592931⟩ Plus de détails...
Following on from Kuhn et al (2010) we study the capability of large eddy simulation with conjugate heat transfer to predict thermal fluctuations with thermal mixing. Wall functions are used to model the wall heat transfer. Comparison with experimental results show that the temperature variance on the outer skin of the solid is well predicted by the simulation. It is shown that the variance of thermal flux in the fluid closely maps the temperature variance at the outer boundary of the solid. Since the variance of thermal flux is closely related to the dissipation of temperature variance it can be concluded that the dissipation of temperature variance in the fluid is linked to temperature variance in the solid. Analysis of the equation of the temperature variance in the solid confirms this is indeed the case. It is the dissipation of temperature variance in the fluid that characterizes how the temperature variance penetrates the solid. Thus RANS modelling can be used to predict thermal variance in solids provided that there is an accurate model for the dissipation of temperature variance at the wall and an equation for the thermal variance in the solid is solved.
R.J.A. Howard, Eric Serre. Large eddy simulation in Code_Saturne of thermal mixing in a T junction with brass walls. International Journal of Heat and Fluid Flow, 2017, 63, pp.119 - 127. ⟨10.1016/j.ijheatfluidflow.2016.09.011⟩. ⟨hal-01592931⟩
Journal: International Journal of Heat and Fluid Flow
A novel immersed boundary method is introduced for simulating the fluid-structure interaction problem. Unlike the body-conforming mesh method which imposes the no-slip boundary conditions directly on the immersed interface, the immersed boundary method adopts a boundary force for the presence of the immersed solid. Therefore, the fluid is simply simulated on a fixed Cartesian mesh irrespective the movement of the immersed solid, which circumvents the mesh quality issue that frequently happens in the body-conforming mesh method. To enforce the correct boundary condition, we derive an additional moving force equation. This additional equation is integrated into a second order accurate fractional step method and solved with the conjugate gradient method. The proposed method is validated with several one-way fluid-structure interaction examples.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Implicit immersed boundary method for fluid-structure interaction. La Houille Blanche - Revue internationale de l'eau, 2017, 1/2017 (1), pp.33 - 36. ⟨10.1051/lhb/2017005⟩. ⟨hal-01592851⟩
Journal: La Houille Blanche - Revue internationale de l'eau
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, 2017, 187, pp.293-305. ⟨10.1016/j.ecss.2017.01.010⟩. ⟨hal-01453377⟩ Plus de détails...
The paper concerns the wind influence on bottom shear stress and salinity levels in a Mediterranean semi-enclosed coastal lagoon (Etang de Berre), with respect to a replanting program of Zostera noltii . The MARS3D numerical model is used to analyze the 3D current, salinity and temperature distribution induced by three meteorological, oceanic and anthropogenic forcings in this lagoon. The numerical model has been carefully validated by comparison with daily observations of the vertical salinity and temperature profiles at three mooring stations, for one year. Then, two modelling scenarios are considered. The first scenario (scen.## 1), starting with an homogeneous salinity of S = 20 PSU and without wind forcing, studies a stratification process under the influence of a periodic seawater inflow and a strong freshwater inflow from an hydropower plant (250 m3/s). Then, in the second scenario (scen.## 2), we study how a strong wind of 80 km/h can mix the haline stratification obtained at the end of scen.## 1. The most interesting results concern four nearshore replanting areas; two are situated on the eastern side of EB and two on the western side. The results of scen.## 2 show that all these areas are subject to a downwind coastal jet. Concerning bottom salinity, the destratification process is very beneficial; it always remains greater than 12 PSU for a N-NW wind of 80 km/h and an hydropower runoff of 250 m3/s. Special attention is devoted to the bottom shear stress (BSS) for different values of the bottom roughness parameter (for gravels, sands and silts), and to the bottom salinity. Concerning BSS, it presents a maximum near the shoreline and decreases along transects perpendicular to the shoreline. There exists a zone, parallel to the shoreline, where BSS presents a minimum (close to zero). When comparing the BSS value at the four replanting areas with the critical value, BSScr, at which the sediment mobility would occur, we see that for the smaller roughness values (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-2 mm) BSS largely surpasses this critical value. For a N-NW wind speed of 40 km/h (which is blowing for around 100 days per year), BSS still largely surpasses BSScr - at least for the silt sediments (ranging from z0 = 3.5 × 10-4 mm, to 3.5 × 10-3 mm). This confirms the possibility that the coastal jet could generate sediment mobility which could have a negative impact for SAV replanting.
E Alekseenko, B Roux, D Fougere, Paul G. Chen. The effect of wind induced bottom shear stress and salinity on Zostera noltii replanting in a Mediterranean coastal lagoon. Estuarine, Coastal and Shelf Science, 2017, 187, pp.293-305. ⟨10.1016/j.ecss.2017.01.010⟩. ⟨hal-01453377⟩
Zhe Li, Julien Favier. A non-staggered coupling of finite element and lattice Boltzmann methods via an immersed boundary scheme for fluid-structure interaction. Computers and Fluids, 2017, 143, pp.90 - 102. ⟨10.1016/j.compfluid.2016.11.008⟩. ⟨hal-01403915⟩ Plus de détails...
The paper presents a numerical framework for the coupling of finite element and lattice Boltzmann methods for transient problems involving fluid-structure interaction. The solid structure is discretized with the finite element method and integrated in time with the explicit Newmark scheme. The lattice Boltzmann method is used for the simulation of single-component weakly-compressible fluid flows. The two numerical methods are coupled via a direct-forcing immersed boundary method in a non-staggered way. Without subiteration within each time-step, the proposed method can ensure the synchronization of the time integrations, and thus the strong coupling of both subdomains by resolving a linear system of coupling equations at each time-step. Hence the energy transfer at the fluid-solid interface is correct, i.e. neither energy dissipation nor energy injection will occur at the interface, which can retain the numerical stability. A well-known fluid-structure interaction test case is adopted to validate the proposed coupling method. It is shown that the stability of the used numerical schemes can be preserved and a good agreement is found with the reference results.
Zhe Li, Julien Favier. A non-staggered coupling of finite element and lattice Boltzmann methods via an immersed boundary scheme for fluid-structure interaction. Computers and Fluids, 2017, 143, pp.90 - 102. ⟨10.1016/j.compfluid.2016.11.008⟩. ⟨hal-01403915⟩
Hugo Bufferand, C Baudoin, J Bucalossi, G Ciraolo, Julien Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D-EIRENE. Nuclear Materials and Energy, 2017, 12, pp.852-857. ⟨hal-01372986⟩ Plus de détails...
In order to improve cross-field transport description, drifts and currents have been implemented in SOLEDGE2D-EIRENE. The derivation of an equation for the electric potential is recalled. The resolution of current equation is tested in a simple slab case. WEST divertor simulations in forward-B and reverse-B fields are also discussed. A significant increase of ExB shear is observed in the forward-B configuration that could explain a favorable L-H transition in this case.
Hugo Bufferand, C Baudoin, J Bucalossi, G Ciraolo, Julien Denis, et al.. Implementation of drift velocities and currents in SOLEDGE2D-EIRENE. Nuclear Materials and Energy, 2017, 12, pp.852-857. ⟨hal-01372986⟩
O. Kazakov, J. Ongena, E. Lerche, M. Mantsinen, D. Van eester, et al.. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, 2017, 13 (10), pp.973-978. ⟨10.1038/NPHYS4167⟩. ⟨cea-01898634⟩ Plus de détails...
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of $^3$He ions to high energies in dedicated hydrogen–deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast $^3$He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, $^3$He-rich solar flares.
O. Kazakov, J. Ongena, E. Lerche, M. Mantsinen, D. Van eester, et al.. Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating. Nature Physics, 2017, 13 (10), pp.973-978. ⟨10.1038/NPHYS4167⟩. ⟨cea-01898634⟩
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, 2017, 44 (1), pp.220 - 228. ⟨10.1109/JOE.2017.2775978⟩. ⟨hal-01702364⟩ Plus de détails...
Sound-source localization in shallow water is a difficult task due to the complicated environment, e.g., complex sound-speed profile and irregular water bottom reflections. Full-wave numerical techniques are currently able to accurately simulate the propagation of sound waves in such complex environments. However, the source localization problem, which generally involves a large number of sound propagation calculations, still requires a fast computation of the wave equation, and thus a simplified model is well advised. In this paper, a four-layer model is considered, which is able to approximate a wide range of shallow-water environments, particularly those in summer conditions. More specifically, the medium is assumed to be horizontally stratified and vertically divided into four layers, and the sound speed in each layer is assumed to be constant or varying linearly. Under this assumption, the wave propagation can be rapidly computed via a classical wave number integration method. The main contribution of this paper is to show the suitability of the four-layer model in terms of source localization in a complex (range-dependent) environment. The sound-speed profile is assumed to be vertically irregular and horizontally slowly varying and the bottom is nonflat. In the forward problem, sound propagation in complex underwater environments is simulated via a time-domain full-wave simulation approach called the spectral-element method. The source localization error due to model imprecision is analyzed.
Xun Wang, Shahram Khazaie, Dimitri Komatitsch, Pierre Sagaut. Sound-Source Localization in Range-Dependent Shallow-Water Environments Using a Four-Layer Model. IEEE Journal of Oceanic Engineering, 2017, 44 (1), pp.220 - 228. ⟨10.1109/JOE.2017.2775978⟩. ⟨hal-01702364⟩
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, In press. ⟨hal-01655295⟩ Plus de détails...
The nonlocal expression proposed by Luciani-Mora-Virmont is implemented into a 1D fluid model for the scrape-off layer. Analytic solutions for heat equation are discussed as well as the impact of sheath boundary conditions on the continuity of the temperature profile. The nonlocal heat flux is compared to Spitzer-Härm heat flux for different collisionality.
Hugo Bufferand, G. Ciraolo, P Di Cintio, N Fedorczak, Ph Ghendrih, et al.. Nonlocal heat flux application for Scrape-off Layer plasma. Contributions to Plasma Physics, In press. ⟨hal-01655295⟩
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, 2017, 826, pp.503 - 521. ⟨10.1017/jfm.2017.439⟩. ⟨hal-01585331⟩ Plus de détails...
The flow over an open cavity is an example of supercritical Hopf bifurcation leading to periodic limit-cycle oscillations. One of its distinctive features is the existence of strong higher harmonics, which results in the time-averaged mean flow being strongly linearly unstable. For this class of flows, a simplified formalism capable of unravelling how exactly the instability grows and saturates is lacking. This study builds on previous work by Mantic-Lugo et al. (Phys. Rev. Lett., vol. 113, 2014, 084501) to fill in the gap using a parametrized approximation of an instantaneous, phase-averaged mean flow, coupled in a quasi-static manner to multiple linear harmonic disturbances interacting nonlinearly with one another and feeding back on the mean flow via their Reynolds stresses. This provides a self-consistent modelling of the mean flow-fluctuation interaction, in the sense that all perturbation structures are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations. The first harmonic is sought as the superposition of two components, a linear component generated by the instability and aligned along the leading eigenmode of the mean flow, and a nonlinear orthogonal component generated by the higher harmonics, which progressively distorts the linear growth rate and eigenfrequency of the eigenmode. Saturation occurs when the growth rate of the first harmonic is zero, at which point the stabilizing effect of the second harmonic balances exactly the linear instability of the eigenmode. The model does not require any input from numerical or experimental data, and accurately predicts the transient development and the saturation of the instability, as established from comparison to time and phase averages of direct numerical simulation data.
Philippe Meliga. Harmonics generation and the mechanics of saturation in flow over an open cavity: a second-order self-consistent description. Journal of Fluid Mechanics, 2017, 826, pp.503 - 521. ⟨10.1017/jfm.2017.439⟩. ⟨hal-01585331⟩
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, 2017, 57 (10), pp.102001. ⟨10.1088/1741-4326/aa5e28⟩. ⟨hal-01660974⟩ Plus de détails...
The 2014-2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L-H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H = 1 at beta(N) similar to 1.8 and n/n(GW) similar to 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D-T campaign and 14 MeV neutron calibration strategy are reviewed.
X. Litaudon, S. Abduallev, M. Abhangi, P. Abreu, M. Afzal, et al.. Overview of the JET results in support to ITER. Nuclear Fusion, 2017, 57 (10), pp.102001. ⟨10.1088/1741-4326/aa5e28⟩. ⟨hal-01660974⟩
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Numerical observation of the equipartition regime in a 3D random elastic medium, and discussion of the limiting parameters. Computers & Geosciences, 2017, 102, pp.56-67. ⟨10.1016/j.cageo.2017.02.007⟩. ⟨hal-01473195⟩ Plus de détails...
At long lapse times in the weakly scattering regime, the energy of the coda in a randomly fluctuating isotropic medium is equipartitioned between P and S modes. This behavior is well understood mathematically and physically for full spaces. For realistic domains, analytical results are more scarce and numerical simulations become a valuable tool. This paper discusses, based on numerical simulations of wave propagation in a 3D randomly heterogeneous elastic medium, the transition to an equipartitioned regime of the wave field. Both the time to transition and the value of the ratio of energies after transition are evaluated. Several influencing parameters are discussed, either physical (ratio of background P-and S-velocities, propagation length, variance of the heterogeneities) or numerical (influence of Perfectly Matched Layers). Setting up of a localization regime, inefficient mixture of body waves and small propagation length compared to the transport mean free paths are identified as constraining for the transition toward an equipartition regime.
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Numerical observation of the equipartition regime in a 3D random elastic medium, and discussion of the limiting parameters. Computers & Geosciences, 2017, 102, pp.56-67. ⟨10.1016/j.cageo.2017.02.007⟩. ⟨hal-01473195⟩
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, 2017, 2 (7), pp.073905. ⟨10.1103/PhysRevFluids.2.073905⟩. ⟨hal-01698605⟩ Plus de détails...
We provide in-depth scrutiny of two methods making use of adjoint-based gradients to compute the sensitivity of drag in the two-dimensional, periodic flow past a circular cylinder (Re≲189): first, the time-stepping analysis used in Meliga et al. [Phys. Fluids 26, 104101 (2014)] that relies on classical Navier-Stokes modeling and determines the sensitivity to any generic control force from time-dependent adjoint equations marched backwards in time; and, second, a self-consistent approach building on the model of Mantič-Lugo et al. [Phys. Rev. Lett. 113, 084501 (2014)] to compute semilinear approximations of the sensitivity to the mean and fluctuating components of the force. Both approaches are applied to open-loop control by a small secondary cylinder and allow identifying the sensitive regions without knowledge of the controlled states. The theoretical predictions obtained by time-stepping analysis reproduce well the results obtained by direct numerical simulation of the two-cylinder system. So do the predictions obtained by self-consistent analysis, which corroborates the relevance of the approach as a guideline for efficient and systematic control design in the attempt to reduce drag, even though the Reynolds number is not close to the instability threshold and the oscillation amplitude is not small. This is because, unlike simpler approaches relying on linear stability analysis to predict the main features of the flow unsteadiness, the semilinear framework encompasses rigorously the effect of the control on the mean flow, as well as on the finite-amplitude fluctuation that feeds back nonlinearly onto the mean flow via the formation of Reynolds stresses. Such results are especially promising as the self-consistent approach determines the sensitivity from time-independent equations that can be solved iteratively, which makes it generally less computationally demanding. We ultimately discuss the extent to which relevant information can be gained from a hybrid modeling computing self-consistent sensitivities from the postprocessing of DNS data. Application to alternative control objectives such as increasing the lift and alleviating the fluctuating drag and lift is also discussed.
Philippe Meliga. Computing the sensitivity of drag and lift in flow past a circular cylinder: Time-stepping versus self-consistent analysis. Physical Review Fluids, 2017, 2 (7), pp.073905. ⟨10.1103/PhysRevFluids.2.073905⟩. ⟨hal-01698605⟩
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, 2016, 97 (4, SI), pp.987-1015. ⟨10.1007/s10494-016-9755-0⟩. ⟨hal-01461791⟩ Plus de détails...
We assess experimentally and theoretically the ability of a small control cylinder to alter vortex shedding in turbulent flow past a square cylinder at R e = 22,000. Results are presented in terms of sensitivity maps showing the flow regions where the shedding frequency and amplitude are most affected by the control cylinder. Experimental results are obtained for a ratio 0.02 of the cylinder diameters, over an extended domain covering the wake, the shear layers and the free stream. The shedding frequency can be either decreased or increased, the largest effects being obtained placing the control cylinder at the outer edge of the detached shear layers (associated with frequency decrease) or upstream of the square cylinder (associated with frequency increase, in contrast with previous results obtained for a D-shaped geometry of the main cylinder). In contrast, the oscillation amplitude is rarely decreased, meaning that any variation of the shedding frequency comes at the expense of more intense vortex shedding. These findings are revisited in the frame of a theoretical, linear sensitivity analysis of the time-averaged mean flow, performed using adjoint methods in the frame of Reynolds-averaged Navier-Stokes modeling. We show that the retained approach carries valuable information in view of guiding efficient control strategy, as it allows identifying the main regions yielding either a decrease or an increase of the shedding frequency in striking agreement with the experiments. This is a tremendous timesaving in so far as the controlled states need not be computed, the overall computational cost being roughly that of computing the mean flow. In contrast, performing the sensitivity analysis on the underlying unstable steady state yields flawed predictions, hence stressing the need to encompass some level of mean coherent-coherent perturbations interaction in the linear model.
Philippe Meliga, Olivier Cadot, Eric Serre. Experimental and Theoretical Sensitivity Analysis of Turbulent Flow Past a Square Cylinder. Flow, Turbulence and Combustion, 2016, 97 (4, SI), pp.987-1015. ⟨10.1007/s10494-016-9755-0⟩. ⟨hal-01461791⟩
François Gallaire, Edouard Boujo, Vladislav Mantic-Lugo, Cristobal Arratia, Benjamin Thiria, et al.. Pushing amplitude equations far from threshold: application to the supercritical Hopf bifurcation in the cylinder wake. Fluid Dynamics Research, 2016, 48 (6), ⟨10.1088/0169-5983/48/6/061401⟩. ⟨hal-01461792⟩ Plus de détails...
The purpose of this review article is to push amplitude equations as far as possible from threshold. We focus on the Stuart-Landau amplitude equation describing the supercritical Hopf bifurcation of the flow in the wake of a cylinder for critical Reynolds number Re-c approximate to 46. After having reviewed Stuart's weakly nonlinear multiple-scale expansion method, we first demonstrate the crucial importance of the choice of the critical parameter. For the wake behind a cylinder considered in this paper, choosing. is an element of(2) = Re-c(1)-Re-c(-1) instead of is an element of'(2) = Re-Re-c/Re-c(2) considerably improves the prediction of the Landau equation. Although Sipp and Lebedev (2007 J. Fluid Mech 593 333-58) correctly identified the adequate bifurcation parameter is an element of, they have plotted their results adding an additional linearization, which amounts to using. is an element of' as approximation to is an element of'. We then illustrate the risks of calculating `running' Landau constants by projection formulas at arbitrary values of the control parameter. For the cylinder wake case, this scheme breaks down and diverges close to Re approximate to 100. We propose an interpretation based on the progressive loss of the non-resonant compatibility condition, which is the cornerstone of Stuart's multiple-scale expansion method. We then briefly review a self-consistent model recently introduced in the literature and demonstrate a link between its properties and the above-mentioned failure.
François Gallaire, Edouard Boujo, Vladislav Mantic-Lugo, Cristobal Arratia, Benjamin Thiria, et al.. Pushing amplitude equations far from threshold: application to the supercritical Hopf bifurcation in the cylinder wake. Fluid Dynamics Research, 2016, 48 (6), ⟨10.1088/0169-5983/48/6/061401⟩. ⟨hal-01461792⟩
Luca Margheri, Pierre Sagaut. A hybrid anchored-ANOVA - POD/Kriging method for uncertainty quantification in unsteady high-fidelity CFD simulations. Journal of Computational Physics, 2016, 324, pp.137-173. ⟨10.1016/j.jcp.2016.07.036⟩. ⟨hal-01461789⟩ Plus de détails...
To significantly increase the contribution of numerical computational fluid dynamics (CFD) simulation for risk assessment and decision making, it is important to quantitatively measure the impact of uncertainties to assess the reliability and robustness of the results. As unsteady high-fidelity CFD simulations are becoming the standard for industrial applications, reducing the number of required samples to perform sensitivity (SA) and uncertainty quantification (UQ) analysis is an actual engineering challenge. The novel approach presented in this paper is based on an efficient hybridization between the anchored-ANOVA and the POD/Kriging methods, which have already been used in CFD-UQ realistic applications, and the definition of best practices to achieve global accuracy. The anchored-ANOVA method is used to efficiently reduce the UQ dimension space, while the POD/Kriging is used to smooth and interpolate each anchored-ANOVA term. The main advantages of the proposed method are illustrated through four applications with increasing complexity, most of them based on Large-Eddy Simulation as a high-fidelity CFD tool: the turbulent channel flow, the flow around an isolated bluff-body, a pedestrian wind comfort study in a full scale urban area and an application to toxic gas dispersion in a full scale city area. The proposed c-APK method (anchored-ANOVA-POD/Kriging) inherits the advantages of each key element: interpolation through POD/Kriging precludes the use of quadrature schemes therefore allowing for a more flexible sampling strategy while the ANOVA decomposition allows for a better domain exploration. A comparison of the three methods is given for each application. In addition, the importance of adding flexibility to the control parameters and the choice of the quantity of interest (QoI) are discussed. As a result, global accuracy can be achieved with a reasonable number of samples allowing computationally expensive CFD-UQ analysis. (C) 2016 Elsevier Inc. All rights reserved.
Luca Margheri, Pierre Sagaut. A hybrid anchored-ANOVA - POD/Kriging method for uncertainty quantification in unsteady high-fidelity CFD simulations. Journal of Computational Physics, 2016, 324, pp.137-173. ⟨10.1016/j.jcp.2016.07.036⟩. ⟨hal-01461789⟩
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, 2016, 117, pp.203-218. ⟨10.1016/j.supflu.2016.06.020⟩. ⟨hal-01369830⟩ Plus de détails...
In this study, adsorption in a model binary mixture is investigated near the critical point in a side-heated cavity. The diverging behavior of the equilibrium constant and the Piston effect are taken into account and their influence on the adsorption process is pointed to. The modeling is based on numerical integration of the differential equations, considering the Navier-Stokes equations coupled with the energy and mass diffusion balances. By means of this model, the temperature, density and adsorbed concentration profiles are drawn at different times. Some fundamental concepts about the system’s response to the heating are illustrated. The results reveal that the adsorption process is influenced by the combined effect of several parameters, such as the gravity and the proximity to the critical point. In particular, the adsorbed amount exhibits a reversed dependency on the wall heating very close to the critical point, which confirms the complexity of such a process in binary systems near critical conditions.
Manel Wannassi, Isabelle Raspo. Numerical study of non-isothermal adsorption of Naphthalene in supercritical CO2: behavior near critical point. Journal of Supercritical Fluids, 2016, 117, pp.203-218. ⟨10.1016/j.supflu.2016.06.020⟩. ⟨hal-01369830⟩
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, 2016, 61 (B), pp.366-378. ⟨10.1016/j.ijheatfluidflow.2016.05.013⟩. ⟨hal-01461786⟩ Plus de détails...
The present work reports Direct Numerical Simulations (DNS) of an impinging round jet onto a rotating heated disk in a confined rotor-stator cavity. The geometrical characteristics of the system correspond to the experimental set-up developed by u. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.]. The aspect ratio of the cavity G = h/R-d between the interdisk spacing h and the rotor radius R-d is fixed to 0.02 corresponding to a narrow-gap cavity. The axial Reynolds number Red based on the jet characteristics is also fixed to Re-j = 5300, while the rotational Reynolds number Re-Omega may vary to preserve the swirl parameter N proportional to Re(Omega)dRe(j) (0 <= N <= 2.47) between the present simulations and the experimental data of [J. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.] and [T. D. Nguyen, J. Pelle, S. Harmand, and S. Poncet. PIV measurements of an air jet impinging on an open rotor-stator system. Experiments in Fluids, 53:401-412, 2012.] for comparisons. The results are discussed in terms of radial distributions of the mean velocity components and corresponding Reynolds stress tensor components. The swirl parameter does not modify the size of the recirculation bubble developed along the stator close to the pipe exit. For N >= 1.237, centrifugal effects at the rotor periphery are balanced by a centripetal flow along the stator. Some spiral patterns develop then in the stator boundary layer corresponding to the SRIII instability of [L. Schouveiler, P. Le Gal, and M. P. Chauve. Instabilities of the flow between a rotating and a stationary disk. Journal of Fluid Mechanics, 443:329-350, 2001.] in an enclosed cavity. The numerical results are found to agree particularly well with the experimental data in terms of the distribution of the local Nusselt number along the rotor. Finally, a correlation for its averaged value is proposed according to the swirl parameter. (C) 2016 Elsevier Inc. All rights reserved.
Romain Oguic, Sébastien Poncet, Stéphane Viazzo. High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity. International Journal of Heat and Fluid Flow, 2016, 61 (B), pp.366-378. ⟨10.1016/j.ijheatfluidflow.2016.05.013⟩. ⟨hal-01461786⟩
Journal: International Journal of Heat and Fluid Flow
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, 2016, 321, pp.606-623. ⟨10.1016/j.jcp.2016.05.038⟩. ⟨hal-01461797⟩ Plus de détails...
The new code TOKAM3X simulates plasma turbulence in full torus geometry including the open field lines of the Scrape-off Layer (SOL) and the edge closed field lines region in the vicinity of the separatrix. Based on drift-reduced Braginskii equations, TOKAM3X is able to simulate both limited and diverted plasmas. Turbulence is flux driven by incoming particles from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed so that interactions between large scale flows and turbulence are consistently treated. Based on a domain decomposition, specific numerical schemes are proposed using conservative finite-differences associated to a semi-implicit time advancement. The process computation is multi-threaded and based on MPI and OpenMP libraries. In this paper, fluid model equations are presented together with the proposed numerical methods. The code is verified using the manufactured solution technique and validated through documented simple experiments. Finally, first simulations of edge plasma turbulence in X-point geometry are also introduced in a JET geometry. (C) 2016 Elsevier Inc. All rights reserved.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Davide Galassi, et al.. The TOKAM3X code for edge turbulence fluid simulations of tokamak plasmas in versatile magnetic geometries. Journal of Computational Physics, 2016, 321, pp.606-623. ⟨10.1016/j.jcp.2016.05.038⟩. ⟨hal-01461797⟩
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, 2016, 56 (6-8), pp.569-574. ⟨10.1002/ctpp.201610063⟩. ⟨hal-01455242⟩ Plus de détails...
The impact of a 3D localized particle source on the edge plasma in 3D global turbulence simulations is investigated using the TOKAM3X fluid code. Results apply to advanced fueling methods such as Supersonic Molecular Beam Injection (SMBI) or pellets injection. The fueling source is imposed as a volumetric particle source in the simulations so that the physics leading to the ionization of particles and its localization are not taken into account. As already observed in experiments, the localized particle source strongly perturbs both turbulence and the large scale organization of the edge plasma. The localized increase of the pressure generated by the source drives sonic parallel flows in the plasma, leading to a poloidal redistribution of the particles on the time scale of the source duration. However, the particle deposition also drives localized transverse pressure gradients which impacts the stability of the plasma with respect to interchange processes. The resulting radial transport occurs on a sufficiently fast time scale to compete with the parallel redistribution of particles, leading to immediate radial losses of a significant proportion of the injected particles. Low Field Side (LFS) and High Field Side (HFS) injections exhibit different dynamics due to their interaction with curvature. In particular, HFS particle deposition drives an inward flux leading to differences in the particle deposition efficiency (higher for HFS than LFS). These results demonstrate the importance of taking into account plasma transport in a self-consistent manner when investigating fueling methods. ((c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Patrick Tamain, Hugo Bufferand, L. Carbajal, Yannick Marandet, C. Baudoin, et al.. Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations. Contributions to Plasma Physics, 2016, 56 (6-8), pp.569-574. ⟨10.1002/ctpp.201610063⟩. ⟨hal-01455242⟩
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, 2016, 56 (6-8), pp.555-562. ⟨10.1002/ctpp.201610033⟩. ⟨hal-01455239⟩ Plus de détails...
Cross-field transport in edge tokamak plasmas is known to be dominated by turbulent transport. A dedicated effort has been made to simulate this turbulent transport from first principle models but the numerical cost to run these simulations on the ITER scale remains prohibitive. Edge plasma transport study relies mostly nowadays on so-called transport codes where the turbulent transport is taken into account using effective ad-hoc diffusion coeffecients. In this contribution, we propose to introduce a transport equation for the turbulence intensity in SOLEDGE2D-EIRENE to describe the interchange turbulence properties. Going beyond the empirical diffusive model, this system automatically generates profiles for the turbulent transport and hence reduces the number of degrees of freedom for edge plasma transport codes. We draw inspiration from the k-epsilon model widely used in the neutral fluid community. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Yannick Marandet, J. Bucalossi, et al.. Interchange Turbulence Model for the Edge Plasma in SOLEDGE2D-EIRENE. Contributions to Plasma Physics, 2016, 56 (6-8), pp.555-562. ⟨10.1002/ctpp.201610033⟩. ⟨hal-01455239⟩
Yannick Marandet, Hugo Bufferand, G. Ciraolo, P. Genesio, P. Meliga, et al.. Effect of Statistical Noise on Simulation Results with a Plasma Fluid Code Coupled to a Monte Carlo Kinetic Neutral Code. Contributions to Plasma Physics, 2016, 56 (6-8), pp.604-609. ⟨10.1002/ctpp.201610009⟩. ⟨hal-01455237⟩ Plus de détails...
Power exhaust is one of the major challenges that future devices such as ITER and DEMO will face. Because of the lack of identified scaling parameters, predictions for divertor plasma conditions in these devices have to rely on detailed modelling. Most plasma edge simulations carried out so far rely on transport codes, which most of the times consist of a fluid code for the plasma coupled to a kinetic Monte Carlo (MC) code for neutral particles. One of the main difficulties in interpreting code results is the statistical noise from the MC procedure, which makes it difficult to define a convergence criterion for the simulations. In this work, we elaborate on similarities between noisy transport code simulations and turbulence simulations, and argue that the time averaged solution is a well defined stationary solution for the system. We illustrate these ideas with a simple slab test case with fluid neutrals, to which we add synthetic noise. In this case, the effects of noise are found to be significant only at high noise levels and for large enough correlations times.
Yannick Marandet, Hugo Bufferand, G. Ciraolo, P. Genesio, P. Meliga, et al.. Effect of Statistical Noise on Simulation Results with a Plasma Fluid Code Coupled to a Monte Carlo Kinetic Neutral Code. Contributions to Plasma Physics, 2016, 56 (6-8), pp.604-609. ⟨10.1002/ctpp.201610009⟩. ⟨hal-01455237⟩
Philippe Meliga, Edouard Boujo, François Gallaire. A self-consistent formulation for the sensitivity analysis of finite-amplitude vortex shedding in the cylinder wake. Journal of Fluid Mechanics, 2016, 800, pp.327-357. ⟨10.1017/jfm.2016.390⟩. ⟨hal-01461794⟩ Plus de détails...
We use the adjoint method to compute sensitivity maps for the limit-cycle frequency and amplitude of the Benard von Karmzin vortex street in the wake of a circular cylinder. rfhe sensitivity, analysis is performed in the frame of the semi-linear self consistent model recently introduced by Mamie et al. (Phys. Rev. Lett., vol. 113, 2014, 084501), which allows us to describe accurately the effect of the control on the mean flow-, but also on the finite-amplitude fluctuation that couples back nonlinearly onto the mean flow via the formation of Reynolds stress. The sensitivity is computed with respect to arbitrary steady and synchronous time-harmonic body forces. For a small amplitude of the control, the theoretical variations of the limit-cycle frequency predict well those of the controlled flow, as obtained from either self-consistent modelling or direct numerical simulation of the Navier Stokes equations. This is not the case if the variations are computed in the simpler mean flow approach overlooking the coupling between the mean and fluctuating components of the flow- perturbation induced by the control. The variations of the limit-cycle amplitude (that falls out the scope of the mean flow approach) are also correctly predicted, meaning that the approach can serve as a relevant and systematic guideline to control strongly unstable flows exhibiting non-small, finite amplitudes of oscillation. As an illustration, we apply the method to control by means of a small secondary control cylinder and discuss the obtained results in the light of the seminal experiments of Strykowski & Sreenivasan
Philippe Meliga, Edouard Boujo, François Gallaire. A self-consistent formulation for the sensitivity analysis of finite-amplitude vortex shedding in the cylinder wake. Journal of Fluid Mechanics, 2016, 800, pp.327-357. ⟨10.1017/jfm.2016.390⟩. ⟨hal-01461794⟩
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, 2016, 56 (6-8), pp.575-580. ⟨10.1002/ctpp.201610038⟩. ⟨hal-01455240⟩ Plus de détails...
The interplay between Langmuir probes (LP) and Scrape-Off-Layer plasma turbulence is numerically investigated with the TOKAM2D and TOKAM3X fluid codes. The LP is modelled by biasing a part of the target plates surface; we then study its impact on the turbulent transport 1) in presence of electron temperature fluctuations and 2) with a complete description of the parallel dynamics. We find that a biased probe can disturb local plasma parameters as well as turbulent transport in its vicinity, by polarizing the connected flux tube and thus driving a strong ExB vortex. Moreover, electron temperature fluctuations are found to account significantly those of floating potential, but with a limited impact on flux measurements depending on the probe's exact geometry. The 3D study of the problem shows the attenuation, but the persistency, of these perturbations induced by the presence of the LP. ((c) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
R. Futtersack, C. Colin, Patrick Tamain, Guido Ciraolo, Philippe Ghendrih, et al.. First Principle Modelling of Interplay between Langmuir Probes and Plasma Turbulence. Contributions to Plasma Physics, 2016, 56 (6-8), pp.575-580. ⟨10.1002/ctpp.201610038⟩. ⟨hal-01455240⟩
Vincent Mons, Jean-Camille Chassaing, Thomas Gomez, Pierre Sagaut. Reconstruction of unsteady viscous flows using data assimilation schemes. Journal of Computational Physics, 2016, 316, pp.255-280. ⟨10.1016/j.jcp.2016.04.022⟩. ⟨hal-01333881⟩ Plus de détails...
This paper investigates the use of various data assimilation (DA) approaches for the reconstruction of the unsteady flow past a cylinder in the presence of incident coherent gusts. Variational, ensemble Kalman filter-based and ensemble-based variational DA techniques are deployed along with a 2D compressible Navier–Stokes flow solver, which is also used to generate synthetic observations of a reference flow. The performance of these DA schemes is thoroughly analyzed for various types of observations ranging from the global aerodynamic coefficients of the cylinder to the full 2D flow field. Moreover, different reconstruction scenarios are investigated in order to assess the robustness of these methods for large scale DA problems with up to 105 control variables. In particular, we show how an iterative procedure can be used within the framework of ensemble-based methods to deal with both non-uniform unsteady boundary conditions and initial field reconstruction. The different methodologies developed and assessed in this work give a review of what can be done with DA schemes in computational fluid dynamics (CFD) paradigm. In the same time, this work also provides useful information which can also turn out to be rational arguments in the DA scheme choice dedicated to a specific CFD application.
Vincent Mons, Jean-Camille Chassaing, Thomas Gomez, Pierre Sagaut. Reconstruction of unsteady viscous flows using data assimilation schemes. Journal of Computational Physics, 2016, 316, pp.255-280. ⟨10.1016/j.jcp.2016.04.022⟩. ⟨hal-01333881⟩
Marianna Pepona, Julien Favier. A coupled Immersed Boundary – Lattice Boltzmann method for incompressible flows through moving porous media A coupled Immersed Boundary -Lattice Boltzmann method for incompressible flows through moving porous media. Journal of Computational Physics, 2016, 321, pp.1170-1184. ⟨10.1016/j.jcp.2016.06.026⟩. ⟨hal-01336315⟩ Plus de détails...
In this work, we propose a numerical framework to simulate fluid flows in interaction with moving porous media of complex geometry. It is based on the Lattice Boltzmann method including porous effects via a Brinkman-Forchheimer-Darcy force model coupled to the Immersed Boundary method to handle complex ge-ometries and moving structures. The coupling algorithm is described in detail and it is validated on well-established literature test cases for both stationary and moving porous configurations. The proposed method is easy to implement and efficient in terms of CPU cost and memory management compared to alternative methods which can be used to deal with moving immersed porous media, e.g. re-meshing at each time step or use of a moving/chimera mesh. An overall good agreement was obtained with reference results, opening the way to the numerical simulation of moving porous media for flow control applications.
Marianna Pepona, Julien Favier. A coupled Immersed Boundary – Lattice Boltzmann method for incompressible flows through moving porous media A coupled Immersed Boundary -Lattice Boltzmann method for incompressible flows through moving porous media. Journal of Computational Physics, 2016, 321, pp.1170-1184. ⟨10.1016/j.jcp.2016.06.026⟩. ⟨hal-01336315⟩
Antoine Briard, Thomas Gomez, Vincent Mons, Pierre Sagaut. Decay and growth laws in homogeneous shear turbulence. Journal of Turbulence, 2016, 17 (7), pp.699 - 726. ⟨10.1080/14685248.2016.1191641⟩. ⟨hal-01429646⟩ Plus de détails...
Homogeneous anisotropic turbulence has been widely studied in the past decades, both numerically and experimentally. Shear flows have received a particular attention because of the numerous physical phenomena they exhibit. In the present paper, both the decay and growth of anisotropy in homogeneous shear flows at high Reynolds numbers are revisited thanks to a recent eddy-damped quasi-normal Markovian (EDQNM) closure adapted to homogeneous anisotropic turbulence. The emphasis is put on several aspects: an asymptotic model for the slow-part of the pressure-strain tensor is derived for the return to isotropy process when mean-velocity gradients are released. Then, a general decay law for purely anisotropic quantities in Batchelor turbulence is proposed. At last, a discussion is proposed to explain the scattering of global quantities obtained in DNS and experiments in sustained shear flows: the emphasis is put on the exponential growth rate of the kinetic energy and on the shear parameter.
Antoine Briard, Thomas Gomez, Vincent Mons, Pierre Sagaut. Decay and growth laws in homogeneous shear turbulence. Journal of Turbulence, 2016, 17 (7), pp.699 - 726. ⟨10.1080/14685248.2016.1191641⟩. ⟨hal-01429646⟩
Yongliang Feng, Pierre Sagaut, Wen-Quan Tao. A compressible lattice Boltzmann finite volume model for high subsonic and transonic flows on regular lattices. Computers and Fluids, 2016, 131, pp.45-55. ⟨10.1016/j.compfluid.2016.03.009⟩. ⟨hal-01461781⟩ Plus de détails...
A multi-dimensional double distribution function thermal lattice Boltzmann model has been developed to simulate fully compressible flows at moderate Mach number. The lattice Boltzmann equation is temporally and spatially discretizated by an asymptotic preserving finite volume scheme. The micro-velocities discretization is adopted on regular low-symmetry lattices (D1Q3, D2Q9, D3Q15, D3Q19, D3Q27). The third-order Hermite polynomial density distribution function on low-symmetry lattices is used to solve the flow field, while a second-order energy distribution is employed to compute the temperature field. The fully compressible Navier-Stokes equations are recovered by standard order Gauss-Hermite polynomial expansions of Maxwell distribution with cubic correction terms, which are added by an external force expressed in orthogonal polynomials form. The proposed model is validated considering several benchmark cases, namely the Sod shock tube, thermal Couette flow and two-dimensional Riemann problem. The numerical results are in very good agreement with both analytical solution and reference results. (C) 2016 Elsevier Ltd. All rights reserved.
Yongliang Feng, Pierre Sagaut, Wen-Quan Tao. A compressible lattice Boltzmann finite volume model for high subsonic and transonic flows on regular lattices. Computers and Fluids, 2016, 131, pp.45-55. ⟨10.1016/j.compfluid.2016.03.009⟩. ⟨hal-01461781⟩
Seung-Bu Park, Pierre Gentine, Kai Schneider, Marie Farge. Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence. Journal of the Atmospheric Sciences, 2016, 73 (4), pp.1789-1814. ⟨10.1175/JAS-D-15-0240.1⟩. ⟨hal-01461782⟩ Plus de détails...
Coherent structures, such as updrafts, downdrafts/shells, and environmental subsidence in the boundary and cloud layers of shallow convection, are investigated using a new classification method. Using large-eddy simulation data, the new method first filters out background turbulence and small-scale gravity waves from the coherent part of the flow, composed of turbulent coherent structures and large-scale transporting gravity waves. Then the algorithm divides this coherent flow into ``updrafts,'' ``downdrafts/shells,'' ``subsidence,'' ``ascendance,'' and four other flow structures using an octant analysis. The novel method can systematically track structures from the cloud-free boundary layer to the cloud layer, thus allowing systematic analysis of the fate of updrafts and downdrafts. The frequency and contribution of the coherent structures to the vertical mass flux and transport of heat and moisture can then be investigated for the first time. Updrafts, subsidence, and downdrafts/subsiding shells-to a lesser extent-are shown to be the most frequent and dominant contributors to the vertical transport of heat and moisture in the boundary layer. Contrary to previous perspective, environmental subsidence transport is shown to be weak in the cloud layer. Instead, downdrafts/shells are the main downward transport contributors, especially in the trade inversion layer. The newly developed method in this study can be used to better evaluate the entrainment and detrainment of individual-or an ensemble of-coherent structures from the unsaturated boundary layer to the cloud layer.
Seung-Bu Park, Pierre Gentine, Kai Schneider, Marie Farge. Coherent Structures in the Boundary and Cloud Layers: Role of Updrafts, Subsiding Shells, and Environmental Subsidence. Journal of the Atmospheric Sciences, 2016, 73 (4), pp.1789-1814. ⟨10.1175/JAS-D-15-0240.1⟩. ⟨hal-01461782⟩
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, 2016, 58 (4), ⟨10.1088/0741-3335/58/4/044005⟩. ⟨hal-01461784⟩ Plus de détails...
Three-dimensional and two-dimensional seeded blob simulations are performed with five different fluid models, all based on the drift-reduced Braginskii equations, and the numerical results are compared among themselves and validated against experimental measurements provided by the TORPEX device ( Fasoli et al 2006 Phys. Plasmas 13 055902). The five models are implemented in four simulation codes, typically used to simulate the plasma dynamics in the tokamak scrape-off layer, namely BOUT++ (Dudson et al 2009 Comput. Phys. Commun. 180 1467), GBS (Ricci et al 2012 Plasma Phys. Control. Fusion 54 124047), HESEL (Nielsen et al 2015 Phys. Lett. A 379 3097), and TOKAM3X (Tamain et al 2014 Contrib. Plasma Phys. 54 555). Three blobs with different velocities and different stability properties are simulated. The differences observed among the simulation results and the different levels of agreement with experimental measurements are investigated, increasing our confidence in our simulation tools and shedding light on the blob dynamics. The comparisons demonstrate that the radial blob dynamics observed in the three-dimensional simulations is in good agreement with experimental measurements and that, in the present experimental scenario, the two-dimensional model derived under the assumption of k(vertical bar vertical bar) = 0 is able to recover the blob dynamics observed in the three-dimensional simulations. Moreover, it is found that an accurate measurement of the blob temperature is important to perform reliable seeded blob simulations.
Fabio Riva, Clothilde Colin, Julien Denis, Luke Easy, Ivo Furno, et al.. Blob dynamics in the TORPEX experiment: a multi-code validation. Plasma Physics and Controlled Fusion, 2016, 58 (4), ⟨10.1088/0741-3335/58/4/044005⟩. ⟨hal-01461784⟩
Amaury Bannier, Eric Garnier, Pierre Sagaut. Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer. Physics of Fluids, 2016, 28 (035108), 16 p. ⟨10.1063/1.4943625⟩. ⟨hal-01428632⟩ Plus de détails...
Various control strategies, such as active feedback control or riblets, end up restraining near-wall turbulence. An analytical study is conducted to estimate the drag-reduction achievable by such control in zero-pressure-gradient turbulent boundary-layers. Based on an idealized control which damps all fluctuations within a near-wall layer, a composite flow profile is established. It leads to explicit models for both the drag-reduction and the boundary-layer development rate. A skin-friction decomposition is applied and gives physical insights on the underlying phenomena. The control is found to alter the spatial development of the boundary-layer, resulting in detrimental impact on the skin-friction. However, the drag-reducing mechanism, attributed to the turbulence weakening, is found predominant and massive drag reductions remain achievable at high Reynolds number, although a minute part of the boundary-layer is manipulated. The model is finally assessed against Large Eddy Simulations of riblet-controlled flow.
Amaury Bannier, Eric Garnier, Pierre Sagaut. Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer. Physics of Fluids, 2016, 28 (035108), 16 p. ⟨10.1063/1.4943625⟩. ⟨hal-01428632⟩
Aerodynamic ground effect in flapping-wing insect flight is of importance to comparative morphologies and of interest to the micro-air-vehicle (MAV) community. Recent studies, however, show apparently contradictory results of either some significant extra lift or power savings, or zero ground effect. Here we present a numerical study of fruitfly sized insect takeoff with a specific focus on the significance of leg thrust and wing kinematics. Flapping-wing takeoff is studied using numerical modelling and high performance computing. The aerodynamic forces are calculated using a three-dimensional Navier--Stokes solver based on a pseudo-spectral method with volume penalization. It is coupled with a flight dynamics solver that accounts for the body weight, inertia and the leg thrust, while only having two degrees of freedom: the vertical and the longitudinal horizontal displacement. The natural voluntary takeoff of a fruitfly is considered as reference. The parameters of the model are then varied to explore possible effects of interaction between the flapping-wing model and the ground plane. These modified takeoffs include cases with decreased leg thrust parameter, and/or with periodic wing kinematics, constant body pitch angle. The results show that the ground effect during natural voluntary takeoff is negligible. In the modified takeoffs, when the rate of climb is slow, the difference in the aerodynamic forces due to the interaction with the ground is up to 6%. Surprisingly, depending on the kinematics, the difference is either positive or negative, in contrast to the intuition based on the helicopter theory, which suggests positive excess lift. This effect is attributed to unsteady wing-wake interactions. A similar effect is found during hovering.
Dmitry Kolomenskiy, Masateru Maeda, Thomas Engels, Hao Liu, Kai Schneider, et al.. Aerodynamic Ground Effect in Fruitfly Sized Insect Takeoff. PLoS ONE, 2016, 11 (3), pp.e0152072. ⟨10.1371/journal.pone.0152072⟩. ⟨hal-01299261⟩
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, 2016, 200, pp.76-86. ⟨10.1016/j.cpc.2015.11.002⟩. ⟨hal-01461783⟩ Plus de détails...
A generic coupling method between a multi-physics workflow engine and an optimization framework is presented in this paper. The coupling architecture has been developed in order to preserve the integrity of the two frameworks. The objective is to provide the possibility to replace a framework, a workflow or an optimizer by another one without changing the whole coupling procedure or modifying the main content in each framework. The coupling is achieved by using a socket-based communication library for exchanging data between the two frameworks. Among a number of algorithms provided by optimization frameworks, Genetic Algorithms (GAs) have demonstrated their efficiency on single and multiple criteria optimization. Additionally to their robustness, GAs can handle non-valid data which may appear during the optimization. Consequently GAs work on most general cases. A parallelized framework has been developed to reduce the time spent for optimizations and evaluation of large samples. A test has shown a good scaling efficiency of this parallelized framework. This coupling method has been applied to the case of SYCOMORE (System COde for MOdeling tokamak REactor) which is a system code developed in form of a modular workflow for designing magnetic fusion reactors. The coupling of SYCOMORE with the optimization platform URANIE enables design optimization along various figures of merit and constraints. (C) 2015 EURATOM. Published by Elsevier B.V. All rights reserved.
Luc Di Gallo, Cédric Reux, Frédéric Imbeaux, Jean-François Artaud, Michal Owsiak, et al.. Coupling between a multi-physics workflow engine and an optimization framework. Computer Physics Communications, 2016, 200, pp.76-86. ⟨10.1016/j.cpc.2015.11.002⟩. ⟨hal-01461783⟩
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga. A Powell-Sabin finite element scheme for partial differential equations . ESAIM: Proceedings, 2016, 53, pp.64-76. ⟨10.1051/proc/201653005⟩. ⟨hal-01377903⟩ Plus de détails...
In this paper are analyzed finite element methods based on Powell-Sabin splines, for the solution of partial differential equations in two dimensions. PS splines are piecewise quadratic polynomials defined on a triangulation of the domain, and exhibit a global C 1 continuity. Critical issues when dealing with PS splines, and described in this work, are the construction of the shape functions and the imposition of the boundary conditions. The PS finite element method is used at first to solve an elliptic problem describing plasma equilibrium in a tokamak. Finally, a transient convective problem is also considered, and a stabilized formulation is presented.
Giorgio Giorgiani, Hervé Guillard, Boniface Nkonga. A Powell-Sabin finite element scheme for partial differential equations . ESAIM: Proceedings, 2016, 53, pp.64-76. ⟨10.1051/proc/201653005⟩. ⟨hal-01377903⟩
Julien Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, 2016, 15th International Conference on Plasma-Facing Materials and Components for Fusion Applications, T167, ⟨10.1088/0031-8949/T167/1/014073⟩. ⟨hal-01459103⟩ Plus de détails...
A thermal wall model is developed for the SolEdge2D-EIRENE edge transport code for calculating the surface temperature of the actively-cooled vessel components in interaction with the plasma. This is a first step towards a self-consistent evaluation of the recycling of particles, which depends on the wall surface temperature. The proposed thermal model is built to match both steady-state temperature and time constant of actively-cooled plasma facing components. A benchmark between this model and the Finite Element Modelling code CAST3M is performed in the case of an ITER-like monoblock. An example of application is presented for a SolEdge2D-EIRENE simulation of a medium-power discharge in the WEST tokamak, showing the steady-state wall temperature distribution and the temperature cycling due to an imposed Edge Localised Mode-like event.
Julien Denis, B. Pégourié, J. Bucalossi, Hugo Bufferand, Guido Ciraolo, et al.. Wall surface temperature calculation in the SolEdge2D-EIRENE transport code. Physica Scripta, 2016, 15th International Conference on Plasma-Facing Materials and Components for Fusion Applications, T167, ⟨10.1088/0031-8949/T167/1/014073⟩. ⟨hal-01459103⟩
Claire David, Pierre Sagaut. Structural stability of Lattice Boltzmann schemes. Physica A: Statistical Mechanics and its Applications, 2016, 444, pp.1-8. ⟨10.1016/j.physa.2015.09.089⟩. ⟨hal-01298987⟩ Plus de détails...
The goal of this work is to determine classes of traveling solitary wave solutions for Lattice Boltzmann schemes by means of an hyperbolic ansatz. It is shown that spurious solitary waves can occur in finite-difference solutions of nonlinear wave equation. The occurence of such a spurious solitary wave, which exhibits a very long life time, results in a non-vanishing numerical error for arbitrary time in unbounded numerical domain. Such a behavior is referred here to have a structural instability of the scheme, since the space of solutions spanned by the numerical scheme encompasses types of solutions (solitary waves in the present case) that are not solutions of the original continuous equations. This paper extends our previous work about classical schemes to Lattice Boltzmann schemes ([1], [2], [3],[4]).
Claire David, Pierre Sagaut. Structural stability of Lattice Boltzmann schemes. Physica A: Statistical Mechanics and its Applications, 2016, 444, pp.1-8. ⟨10.1016/j.physa.2015.09.089⟩. ⟨hal-01298987⟩
Journal: Physica A: Statistical Mechanics and its Applications
Frank G. Jacobitz, Kai Schneider, Wouter J.T. Bos, Marie Farge. Structure of sheared and rotating turbulence: Multiscale statistics of Lagrangian and Eulerian accelerations and passive scalar dynamics. Physical Review E , 2016, 93 (1), pp.013113. ⟨10.1103/PhysRevE.93.013113⟩. ⟨hal-01299256⟩ Plus de détails...
The acceleration statistics of sheared and rotating homogeneous turbulence are studied using direct numerical simulation results. The statistical properties of Lagrangian and Eulerian accelerations are considered together with the influence of the rotation to shear ratio, as well as the scale dependence of their statistics. The probability density functions (pdfs) of both Lagrangian and Eulerian accelerations show a strong and similar dependence on the rotation to shear ratio. The variance and flatness of both accelerations are analyzed and the extreme values of the Eulerian acceleration are observed to be above those of the Lagrangian acceleration. For strong rotation it is observed that flatness yields values close to three, corresponding to Gaussian-like behavior, and for moderate and vanishing rotation the flatness increases. Furthermore, the Lagrangian and Eulerian accelerations are shown to be strongly correlated for strong rotation due to a reduced nonlinear term in this case. A wavelet-based scale-dependent analysis shows that the flatness of both Eulerian and Lagrangian accelerations increases as scale decreases, which provides evidence for intermittent behavior. For strong rotation the Eulerian acceleration is even more intermittent than the Lagrangian acceleration, while the opposite result is obtained for moderate rotation. Moreover, the dynamics of a passive scalar with gradient production in the direction of the mean velocity gradient is analyzed and the influence of the rotation to shear ratio is studied. Concerning the concentration of a passive scalar spread by the flow, the pdf of its Eulerian time rate of change presents higher extreme values than those of its Lagrangian time rate of change. This suggests that the Eulerian time rate of change of scalar concentration is mainly due to advection, while its Lagrangian counterpart is only due to gradient production and viscous dissipation.
Frank G. Jacobitz, Kai Schneider, Wouter J.T. Bos, Marie Farge. Structure of sheared and rotating turbulence: Multiscale statistics of Lagrangian and Eulerian accelerations and passive scalar dynamics. Physical Review E , 2016, 93 (1), pp.013113. ⟨10.1103/PhysRevE.93.013113⟩. ⟨hal-01299256⟩
Shahram Khazaie, Xun Wang, Pierre Sagaut. Localization of random acoustic sources in an inhomogeneous medium. Journal of Sound and Vibration, 2016, 384, pp.75 - 93. ⟨10.1016/j.jsv.2016.08.004⟩. ⟨hal-01375680⟩ Plus de détails...
In this paper, the localization of a random sound source via different source localization methods is considered, the emphasis being put on the robustness and the accuracy of classical methods in the presence of uncertainties. The sound source position is described by a random variable and the sound propagation medium is assumed to have spatially varying parameters with known values. Two approaches are used for the source identification: time reversal and beamforming. The probability density functions of the random source position are estimated using both methods. The focal spot resolutions of the time reversal estimates are also evaluated. In the numerical simulations, two media with different correlation lengths are investigated to account for two different scattering regimes: one has a correlation length relatively larger than the wavelength and the other has a correlation length comparable to the wavelength. The results show that the required sound propagation time and source estimation robustness highly depend on the ratio between the correlation length and the wavelength. It is observed that source identification methods have different robustness in the presence of uncertainties. Advantages and weaknesses of each method are discussed.
Shahram Khazaie, Xun Wang, Pierre Sagaut. Localization of random acoustic sources in an inhomogeneous medium. Journal of Sound and Vibration, 2016, 384, pp.75 - 93. ⟨10.1016/j.jsv.2016.08.004⟩. ⟨hal-01375680⟩
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Influence of the spatial correlation structure of an elastic random medium on its scattering properties. Journal of Sound and Vibration, 2016, 370, pp.132-148. ⟨10.1016/j.jsv.2016.01.012⟩. ⟨hal-01281405⟩ Plus de détails...
In the weakly heterogeneous regime of elastic wave propagation through a random medium, transport and diffusion models for the energy densities can be set up. In the isotropic case, the scattering cross sections are explicitly known as a function of the wave number and the correlations of the Lamé parameters and density. In this paper, we discuss the precise influence of the correlation structure on the scattering cross sections, mean free paths and diffusion parameter, and separate that influence from that of the correlation length and variance. We also analyze the convergence rates towards the low-and high-frequency ranges. For all analyses, we consider five different correlation structures, that allow us to explore a wide range of behaviors. We identify that the controlling factors for the low-frequency behavior are the value of the Power Spectral Density Function (PSDF) and its first non-vanishing derivative at the origin. In the high frequency range, the controlling factor is the third moment of the PSDF (which may be unbounded).
Shahram Khazaie, Régis Cottereau, Didier Clouteau. Influence of the spatial correlation structure of an elastic random medium on its scattering properties. Journal of Sound and Vibration, 2016, 370, pp.132-148. ⟨10.1016/j.jsv.2016.01.012⟩. ⟨hal-01281405⟩
I. Thiagalingam, Pierre Sagaut. Pseudo-homogeneous 1D RANS radial model for heat transfer in tubular packed beds. International Journal of Heat and Fluid Flow, 2016, 62 (Part B), pp.258-272. ⟨10.1016/j.ijheatfluidflow.2016.10.005⟩. ⟨hal-01400641⟩ Plus de détails...
A RANS zonal pseudo-homogeneous 1D radial heat transfer model is derived using an homogenization technique along with high-fidelity microscopic simulation to calibrate the model free parameters. Thus, it is brought to light the importance of the mechanical dispersion in the mixing process, the similarity between turbulent and dispersive dynamics, the existence of a near wall zone characterized by a channeling effect which is responsible for the thermal resistance over the zone. A linear law for the effective thermal conductivity is proposed to assess the heat transfer within the disrupted thermal boundary layer. The model showed its ability to estimate the effective conductivity and the temperature field in the radial direction with satisfaction. Very good agreements are also found in the near wall zone where the temperature gradients are the highest. The model well estimated also the value of the wall temperature and the wall heat transfer coefficient for an imposed heat flux at the wall.
I. Thiagalingam, Pierre Sagaut. Pseudo-homogeneous 1D RANS radial model for heat transfer in tubular packed beds. International Journal of Heat and Fluid Flow, 2016, 62 (Part B), pp.258-272. ⟨10.1016/j.ijheatfluidflow.2016.10.005⟩. ⟨hal-01400641⟩
Journal: International Journal of Heat and Fluid Flow
Lyes Bordja, Emilia Crespo Del Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, 2016, 47 (5), pp.471-488. ⟨10.1615/HeatTransRes.2016007441⟩. ⟨hal-01462070⟩ Plus de détails...
The effects of thermal convection and of a constant axial magnetic field on a von Karman flow driven by the exact counter-rotation of two lids are investigated in a vertical cylinder of aspect ratio Gamma(= height/radius) = 2 at a fixed Reynolds number Re(= Omega R-2/v) = 300. Direct numerical simulations are performed when varying separately the Rayleigh and Hartmann numbers in the range [0, 1800] and [0, 20], respectively, in the limit of the Boussinesq approximation and of a small magnetic Reynolds numbers, Re-m << 1. Without a magnetic field, the base flow symmetries of the von Karman flow are broken by thermal convection that becomes dominant in the range of Ra [500, 1000]. Three-dimensional solutions are characterized by the occurrence of a steady, m = 1, azimuthal mode exhibiting a cat's eye vortex in the circumferential plane. When increasing the Rayleigh number in the range [500, 1000], the vortex pulsates in an oscillatory manner, due to variations of the flow intensity. Otherwise, increasing the axial magnetic field intensity stabilizes the flow, and the oscillatory motion can be inhibited. Numerical solutions show that the critical Rayleigh number for transition increases linearly with the Hartmann number. Finally, results show that when varying the Rayleigh number, the structure of the electric potential can be strongly modified by thermal convection. Such an observation suggests new induction mechanisms in the case of small nonzero values of the magnetic Reynolds number.
Lyes Bordja, Emilia Crespo Del Arco, Éric Serre, Rachid Bessaih. EFFECTS OF AXIAL MAGNETIC FIELD AND THERMAL CONVECTION ON A COUNTERROTATING VON KARMAN FLOW. Heat Transfer Research, 2016, 47 (5), pp.471-488. ⟨10.1615/HeatTransRes.2016007441⟩. ⟨hal-01462070⟩
Dmitry Kolomenskiy, Jean-Christophe Nave, Kai Schneider. Adaptive gradient-augmented level set method with multiresolution error estimation. Journal of Scientific Computing, 2016, 66, pp.116-140. ⟨10.1007/s10915-015-0014-7⟩. ⟨hal-01146954⟩ Plus de détails...
A space–time adaptive scheme is presented for solving advection equations in two space dimensions. The gradient-augmented level set method using a semi-Lagrangian formulation with backward time integration is coupled with a point value multiresolution analysis using Hermite interpolation. Thus locally refined dyadic spatial grids are introduced which are efficiently implemented with dynamic quadtree data structures. For adaptive time integration, an embedded Runge–Kutta method is employed. The precision of the new fully adaptive method is analysed and speed up of CPU time and memory compression with respect to the uniform grid discretization are reported.
Dmitry Kolomenskiy, Jean-Christophe Nave, Kai Schneider. Adaptive gradient-augmented level set method with multiresolution error estimation. Journal of Scientific Computing, 2016, 66, pp.116-140. ⟨10.1007/s10915-015-0014-7⟩. ⟨hal-01146954⟩
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, 2016, 788, pp.147-182. ⟨10.1017/jfm.2015.705⟩. ⟨hal-01276637⟩ Plus de détails...
A nonlinear spectral model in terms of spherically averaged descriptors is derived for the prediction of homogeneous turbulence dynamics in the presence of arbitrary mean-velocity gradients. The governing equations for the tensor $\hat{R}_{ij}(\mathbf k,t)$, the Fourier transform of the two-point second-order correlation tensor, are first closed by an anisotropic eddy-damped quasinormal Markovian procedure. This closure is restricted to turbulent flows where linear effects induced by mean-flow gradients have no essential qualitative effects on the dynamics of triple correlations compared with the induced production effects in the equations for second-order correlations. Truncation at the first relevant order of spectral angular dependence allows us to derive from these equations in vector $\mathbf k$ our final model equations in terms of the wavenumber modulus $k$ only. Analytical spherical integration results in a significant decrease in computational cost. Besides, the model remains consistent with the decomposition in terms of directional anisotropy and polarization anisotropy, with a spherically averaged anisotropic spectral tensor for each contribution. Restriction of anisotropy to spherically averaged descriptors, however, entails a loss of information, and realizability conditions are considered to quantify the upper boundary of anisotropy that can be investigated with the proposed model. Several flow configurations are considered to assess the validity of the present model. Satisfactory agreement with experiments on grid-generated turbulence subjected to successive plane strains is observed, which confirms the capability of the model to account for production of anisotropy by mean-flow gradients. The nonlinear transfer terms of the model are further tested by considering the return to isotropy (RTI) of different turbulent flows. Different RTI rates for directional anisotropy and polarization anisotropy allow us to correctly predict the apparent delayed RTI shown after axisymmetric expansion. The last test case deals with homogeneous turbulence subjected to a constant pure plane shear. The interplay between linear and nonlinear effects is reproduced, yielding the eventual exponential growth of the turbulent kinetic energy.
Vincent Mons, Claude Cambon, Pierre Sagaut. A spectral model for homogeneous shear-driven anisotropic turbulence in terms of spherically averaged descriptors. Journal of Fluid Mechanics, 2016, 788, pp.147-182. ⟨10.1017/jfm.2015.705⟩. ⟨hal-01276637⟩
Zhe Li, Julien Favier, Umberto D 'Ortona, Sébastien Poncet. An immersed boundary-lattice Boltzmann method for single- and multi-component fluid flows. Journal of Computational Physics, 2016, 304, pp.424-440. ⟨10.1016/j.jcp.2015.10.026⟩. ⟨hal-01225681⟩ Plus de détails...
The paper presents a numerical method to simulate single-and multi-component fluid flows around moving/deformable solid boundaries, based on the coupling of Immersed Boundary (IB) and Lattice Boltzmann (LB) methods. The fluid domain is simulated with LB method using the single relaxation time BGK model, in which an interparticle potential model is applied for multi-component fluid flows. The IB-related force is directly calculated with the interpolated definition of the fluid macroscopic velocity on the Lagrangian points that define the immersed solid boundary. The present IB-LB method can better ensure the no-slip solid boundary condition, thanks to an improved spreading operator. The proposed method is validated through several 2D/3D single-and multi-component fluid test cases with a particular emphasis on wetting conditions on solid wall. Finally, a 3D two-fluid application case is given to show the feasibility of modeling the fluid transport via a cluster of beating cilia.
Zhe Li, Julien Favier, Umberto D 'Ortona, Sébastien Poncet. An immersed boundary-lattice Boltzmann method for single- and multi-component fluid flows. Journal of Computational Physics, 2016, 304, pp.424-440. ⟨10.1016/j.jcp.2015.10.026⟩. ⟨hal-01225681⟩
Benjamin Kadoch, Thorsten Reimann, Kai Schneider, Michael Schäfer. Comparison of a spectral method with volume penalization and a finite volume method with body fitted grids for turbulent flows. Computers and Fluids, 2016, 133, pp.140-150. ⟨10.1016/j.compfluid.2016.04.028⟩. ⟨hal-01455110⟩ Plus de détails...
We consider a turbulent flow past periodic hills at Reynolds number 1400 and compare two numerical methods: A Fourier pseudo–spectral scheme with volume penalization to model the no-slip boundary conditions and a finite volume method with body fitted grids. A detailed comparison of the results is presented for mean velocity profiles and Reynolds stress and confronted with those obtained by Breuer et al. [1]. In addition higher order statistics are performed and their scale-dependence is analyzed using orthogonal wavelets. Moreover, for the Fourier pseudo-spectral scheme, the influence of the Reynolds number is investigated.
Benjamin Kadoch, Thorsten Reimann, Kai Schneider, Michael Schäfer. Comparison of a spectral method with volume penalization and a finite volume method with body fitted grids for turbulent flows. Computers and Fluids, 2016, 133, pp.140-150. ⟨10.1016/j.compfluid.2016.04.028⟩. ⟨hal-01455110⟩
The problem of flapping filaments in an uniform incoming flow is tackled using a Lattice Boltzmann—Immersed Boundary method. The fluid momentum equations are solved on a Cartesian uniform lattice while the beating filaments are tracked through a series of markers, whose dynamics are functions of the forces exerted by the fluid, the filament flexural rigidity and the tension. The instantaneous wall conditions on the filament are imposed via a system of singular body forces, consistently discretised on the lattice of the Boltzmann equation. We first consider the case of a single beating filament, and then the case of multiple beating filaments in a side-by-side configuration, focussing on the modal behaviour of the whole dynamical systems.
Julien Favier, Alistair Revell, Alfredo Pinelli. Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods. Advances in Fluid-Structure Interaction, 133, Springer, pp.167-178, 2016, Notes on Numerical Fluid Mechanics and Multidisciplinary Design 978-3-319-27384-6. ⟨10.1007/978-3-319-27386-0_10⟩. ⟨hal-01705549⟩
Sergio Croquer, Sébastien Poncet, Zine Aidoun. Turbulence modeling of a single-phase R134a supersonic ejector. Part 1: Numerical benchmark. International Journal of Refrigeration, 2016, 61 (8), pp.140-152. ⟨10.1016/j.ijrefrig.2015.07.030⟩. ⟨hal-01300110⟩ Plus de détails...
The present work reports a numerical analysis of a supersonic ejector in single-phase conditions using R134a as the working fluid. A numerical benchmark of some thermodynamic and two-equation turbulence models has been carried out to highlight the numerical model offering the best compromise between accuracy and calculation cost. The validation is achieved by comparing the predicted entrainment ratio with the experimental data of Garcia del Valle et al. (2014). The k−ω SST model together with the REFPROP 7.0 database equation appears to be the best combination to predict accurately the ejector performance and capture the shock wave structure. The influence of the outlet temperature, the discussion about the validity of some assumptions made by one-dimensional (1D) models and the exergy analysis within the ejector for the present operating conditions will later be discussed in Part 2 (Croquer et al., 2015).
Sergio Croquer, Sébastien Poncet, Zine Aidoun. Turbulence modeling of a single-phase R134a supersonic ejector. Part 1: Numerical benchmark. International Journal of Refrigeration, 2016, 61 (8), pp.140-152. ⟨10.1016/j.ijrefrig.2015.07.030⟩. ⟨hal-01300110⟩
Stationarity is a key tool in classical time series. In order to analyze the set-valued time series, it must be extended to the set-valued case. In this paper, stationary set-valued time series is defined via DpDp metric of set-valued random variables. Then, estimation methods of expectation and auto-covariance function of stationary set-valued time series are proposed. Unbiasedness and consistency of the expectation estimator and asymptotic unbiasedness of the auto-covariance function estimator are justified. After that, a special case of the set-valued time series, known as interval-valued time series, is considered. Two forecast methods of the stationary interval-valued time series are explicitly presented. Furthermore, the interval-valued time series is contextualized in the Box–Jenkins framework: an interval-valued autoregression model, along with its parameter estimation method, is introduced. Finally, experiments on both simulated and real data are presented to justify the efficiency of the parameters estimation method and the availability of the proposed model.
Xun Wang, Zhongzhan Zhang, Shoumei Li. Set-valued and interval-valued stationary time series. Journal of Multivariate Analysis, 2016, 145, pp.208 - 223. ⟨10.1016/j.jmva.2015.12.010⟩. ⟨hal-01450819⟩
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Improved Implicit Immersed Boundary Method via Operator Splitting. Ibrahimbegovic, A. Computational Methods for Solids and Fluids : Multiscale Analysis, Probability Aspects and Model Reduction, 41, Springer, pp.49-66, 2016, Computational Methods in Applied Sciences, 978-3-319-27996-1. ⟨10.1007/978-3-319-27996-1_3⟩. ⟨hal-01462069⟩ Plus de détails...
We present an implicit immersed boundary method via operator splitting technique for simulating fluid flow over moving solid with complex shape. An additional moving force equation is derived in order to impose the interface velocity condition exactly on the immersed surface. The moving force matrix is formulated to be symmetric and positive definite, thus its calculation is computational inexpensive by using the conjugate gradient method. Moreover, the proposed immersed boundary method is incorporated into the rotational incremental projection method as a plug-in. No numerical boundary layers will be generated towards the velocity and pressure during the calculation. The method is validated through various benchmark tests.
Shang-Gui Cai, Abdellatif Ouahsine, Julien Favier, Yannick Hoarau. Improved Implicit Immersed Boundary Method via Operator Splitting. Ibrahimbegovic, A. Computational Methods for Solids and Fluids : Multiscale Analysis, Probability Aspects and Model Reduction, 41, Springer, pp.49-66, 2016, Computational Methods in Applied Sciences, 978-3-319-27996-1. ⟨10.1007/978-3-319-27996-1_3⟩. ⟨hal-01462069⟩
Cai S-G., Ouahsine A., Julien Favier, Hoarau Y.. Improved Implicit Immersed Boundary Method via Operator Splitting, Computational Methods for Solids and Fluids. Multiscale Analysis, Probability Aspects and Model Reduction, Computational Methods in Applied Sciences, Springer, pp.49--66, 2016. ⟨hal-01313518⟩ Plus de détails...
Cai S-G., Ouahsine A., Julien Favier, Hoarau Y.. Improved Implicit Immersed Boundary Method via Operator Splitting, Computational Methods for Solids and Fluids. Multiscale Analysis, Probability Aspects and Model Reduction, Computational Methods in Applied Sciences, Springer, pp.49--66, 2016. ⟨hal-01313518⟩
T. Engels, D. Kolomenskiy, Kai Schneider, F.-O. Lehmann, J. Sesterhenn. Bumblebee Flight in Heavy Turbulence. Physical Review Letters, 2016, 116 (2), pp.028103. ⟨10.1103/PhysRevLett.116.028103⟩. ⟨hal-01299332⟩ Plus de détails...
High-resolution numerical simulations of a tethered model bumblebee in forward flight are performed superimposing homogeneous isotropic turbulent fluctuations to the uniform inflow. Despite tremendous variation in turbulence intensity, between 17% and 99% with respect to the mean flow, we do not find significant changes in cycle-averaged aerodynamic forces, moments or flight power when averaged over realizations, compared to laminar inflow conditions. The variance of aerodynamic measures, however, significantly increases with increasing turbulence intensity, which may explain flight instabilities observed in freely flying bees.
T. Engels, D. Kolomenskiy, Kai Schneider, F.-O. Lehmann, J. Sesterhenn. Bumblebee Flight in Heavy Turbulence. Physical Review Letters, 2016, 116 (2), pp.028103. ⟨10.1103/PhysRevLett.116.028103⟩. ⟨hal-01299332⟩
Kai Schneider. Immersed boundary methods for numerical simulation of confined fluid and plasma turbulence in complex geometries: a review. Journal of Plasma Physics, 2015, 81 (06), pp.435810601. ⟨10.1017/S0022377815000598⟩. ⟨hal-01299254⟩ Plus de détails...
Immersed boundary methods for computing confined fluid and plasma flows in complex geometries are reviewed. The mathematical principle of the volume penalization technique is described and simple examples for imposing Dirichlet and Neumann boundary conditions in one dimension are given. Applications for fluid and plasma turbulence in two and three space dimensions illustrate the applicability and the efficiency of the method in computing flows in complex geometries, for example in toroidal geometries with asymmetric poloidal cross-sections.
Kai Schneider. Immersed boundary methods for numerical simulation of confined fluid and plasma turbulence in complex geometries: a review. Journal of Plasma Physics, 2015, 81 (06), pp.435810601. ⟨10.1017/S0022377815000598⟩. ⟨hal-01299254⟩
Xun Wang, Shahram Khazaie, Pierre Sagaut. Sound source localization in a randomly inhomogeneous medium using matched statistical moment method. Journal of the Acoustical Society of America, 2015, 138 (6), pp.3896. ⟨10.1121/1.4938238⟩. ⟨hal-01276517⟩ Plus de détails...
This paper investigates the problem of sound source localization from acoustical measurements obtained by an array of microphones. The sound propagation medium is assumed to be randomly inhomogeneous, being modelled by a random function of space. In this case, classical source localization methods (e.g., beamforming, near-field acoustical holography, and time reversal) cannot be used anymore. Therefore, an approach based on the statistical moments of acoustical measurement is proposed to solve the aforementioned problem. In this work, a Karhunen–Loève expansion is used so that the random medium can be represented by a small number of uncorrelated and identically distributed random variables. The statistical characteristics of the measurements in terms of probability density function and statistical moments are also studied. Then, the sound source is localized by minimizing the error of statistical moments between the real measurements obtained from the microphone array and the measurements simulated from an assumed source. Finally, a numerical example is introduced to justify the proposed method. This experiment shows that the random field can be replicated by a very small number of random variables, the statistical moments of measurements guarantee the convergence, and the source location can be accurately estimated using the proposed source localization method.
Xun Wang, Shahram Khazaie, Pierre Sagaut. Sound source localization in a randomly inhomogeneous medium using matched statistical moment method. Journal of the Acoustical Society of America, 2015, 138 (6), pp.3896. ⟨10.1121/1.4938238⟩. ⟨hal-01276517⟩
Journal: Journal of the Acoustical Society of America
Yongliang Feng, Pierre Sagaut, Wenquan Tao. A three dimensional lattice model for thermal compressible flow on standard lattices. Journal of Computational Physics, 2015, 303, pp.514-529. ⟨10.1016/j.jcp.2015.09.011⟩. ⟨hal-01276507⟩ Plus de détails...
A three-dimensional double distribution function thermal lattice Boltzmann model has been developed for simulation of thermal compressible flows in the low Mach number limit. Both the flow field and energy conservation equation are solved by LB approach. A higher order density distribution function on standard lattices is used to solve the flow field, while an energy distribution function is employed to compute the temperature field. The equation of state of thermal perfect gas is recovered by higher order Hermite polynomial expansions in Navier–Stokes–Fourier equations. The equilibrium distribution functions of D3Q15, D3Q19 and D3Q27 lattices are obtained from the Hermite expansion. They exhibit slight differences originating in differences in the discrete lattice symmetries. The correction terms in LB models for third order derivation are added using an external force in orthogonal polynomials form. Present models are successfully assessed considering several test cases, namely the thermal Couette flow, Rayleigh–Bénard convection, natural convection in square cavity and a spherical explosion in a 3D enclosed box. The numerical results are in good agreement with both analytical solution and results given by previous authors.
Yongliang Feng, Pierre Sagaut, Wenquan Tao. A three dimensional lattice model for thermal compressible flow on standard lattices. Journal of Computational Physics, 2015, 303, pp.514-529. ⟨10.1016/j.jcp.2015.09.011⟩. ⟨hal-01276507⟩
Antoine Briard, Thomas Gomez, Pierre Sagaut, Souzan Memari. Passive scalar decay laws in isotropic turbulence: Prandtl number effects. Journal of Fluid Mechanics, 2015, 784, pp.274 - 303. ⟨10.1017/jfm.2015.575⟩. ⟨hal-01429641⟩ Plus de détails...
The passive scalar dynamics in a freely decaying turbulent flow is studied. The classical framework of homogeneous isotropic turbulence without forcing is considered. Both low and high Reynolds number regimes are investigated for very small and very large Prandtl numbers. The long time behaviours of integrated quantities such as the scalar variance or the scalar dissipation rate are analyzed by considering that the decay follows power laws. This study addresses three major topics. Firstly, the Comte-Bellot and Corrsin (CBC) dimensional analysis for the temporal decay exponents is extended to the case of a passive scalar when the permanence of large eddies is broken. Secondly, using numerical simulations based on eddy-damped quasi-normal markovian (EDQNM) model, the time evolution of integrated quantities is accurately determined for a wide range of Reynolds and Prandtl numbers. These simulations show that, whatever the Reynolds and the Prandtl numbers are, the decay follows an algebraic law with an exponent very close to the value predicted by the CBC theory. Finally, the initial position of the scalar integral scale L T has no influence on the asymptotic values of the decay exponents, and an analytical law predicting the relative positions of the kinetic and scalar spectra peaks is derived.
Antoine Briard, Thomas Gomez, Pierre Sagaut, Souzan Memari. Passive scalar decay laws in isotropic turbulence: Prandtl number effects. Journal of Fluid Mechanics, 2015, 784, pp.274 - 303. ⟨10.1017/jfm.2015.575⟩. ⟨hal-01429641⟩
Romain Oguic, Stéphane Viazzo, Sébastien Poncet. A parallelized multidomain compact solver for incompressible turbulent flows in cylindrical geometries. Journal of Computational Physics, 2015, 300, pp.710-731. ⟨10.1016/j.jcp.2015.08.003⟩. ⟨hal-01299082⟩ Plus de détails...
We present an efficient parallelized multidomain algorithm for solving the 3D Navier–Stokes equations in cylindrical geometries. The numerical method is based on fourth-order compact schemes in the two non-homogeneous directions and Fourier series expansion in the azimuthal direction. The temporal scheme is a second-order semi-implicit projection scheme leading to the solution of five Helmholtz/Poisson equations. To handle the singularity appearing at the axis in cylindrical coordinates, while being able to have a thinner or conversely a coarser mesh in this zone, parity conditions are imposed at r=0r=0 for each flow variable and azimuthal Fourier mode. To simulate flows in irregularly shaped cylindrical geometries and benefit from a hybrid OpenMP/MPI parallelization, an accurate perfectly free-divergence multidomain method based on the influence matrix technique is proposed. First, the accuracy of the present solver is checked by comparison with analytical solutions and the scalability is then evaluated. Simulations using the present code are then compared to reliable experimental and numerical results of the literature showing good quantitative agreements in the cases of the axisymmetric and 3D unsteady vortex breakdowns in a cylinder and turbulent pipe flow. Finally to show the capability of the algorithm to deal with more complex flows relevant of turbomachineries, the turbulent flow inside a simplified stage of High-Pressure compressor is considered.
Romain Oguic, Stéphane Viazzo, Sébastien Poncet. A parallelized multidomain compact solver for incompressible turbulent flows in cylindrical geometries. Journal of Computational Physics, 2015, 300, pp.710-731. ⟨10.1016/j.jcp.2015.08.003⟩. ⟨hal-01299082⟩
Amaury Bannier, Éric Garnier, Pierre Sagaut. Riblet Flow Model Based on an Extended FIK Identity. Flow, Turbulence and Combustion, 2015, 95 (2-3), pp.351-376. ⟨10.1007/s10494-015-9624-2⟩. ⟨hal-01276488⟩ Plus de détails...
Large Eddy Simulations of zero-pressure-gradient turbulent boundary layers over riblets have been conducted. All along the controlled domain, riblets maintain a significant 11 % drag reduction with respect to the flat plate at the same R e τ (from 250 to 450). To compare the flows above riblets and a reference smooth wall, an appropriate vertical shift between the two surfaces is required. In the present study, the “vertical origin” is set using the identity of Fukagata, Iwamoto and Kasagi (FIK) in Phys. Fluids, vol. 14, 2002, L73. This identity, which provides a physically meaningful decomposition of the skin friction, has been extended to complex wall surfaces and constitutes the basis for the derivation of a new virtual origin. Using this FIK-based origin, it is shown that the complex interactions between the riblets and the near-wall turbulent structures can be taken into account by a simple shift of the two axes of the mean and turbulent velocity profiles. The appropriate upward shift Δu +, typical for drag reduction, is directly dependent on the skin friction on the riblets and on the reference smooth plate at the same R e τ .
Amaury Bannier, Éric Garnier, Pierre Sagaut. Riblet Flow Model Based on an Extended FIK Identity. Flow, Turbulence and Combustion, 2015, 95 (2-3), pp.351-376. ⟨10.1007/s10494-015-9624-2⟩. ⟨hal-01276488⟩
Dmitry Kolomenskiy, Romain Nguyen van Yen, Kai Schneider. Analysis and discretization of the volume penalized Laplace operator with Neumann boundary conditions. Applied Numerical Mathematics: an IMACS journal, 2015, 95, pp.238-249. ⟨10.1016/j.apnum.2014.02.003⟩. ⟨hal-01299247⟩ Plus de détails...
We study the properties of an approximation of the Laplace operator with Neumann boundary conditions using volume penalization. For the one-dimensional Poisson equation we compute explicitly the exact solution of the penalized equation and quantify the penalization error. Numerical simulations using finite differences allow then to assess the discretization and penalization errors. The eigenvalue problem of the penalized Laplace operator with Neumann boundary conditions is also studied. As examples in two space dimensions, we consider a Poisson equation with Neumann boundary conditions in rectangular and circular domains.
Dmitry Kolomenskiy, Romain Nguyen van Yen, Kai Schneider. Analysis and discretization of the volume penalized Laplace operator with Neumann boundary conditions. Applied Numerical Mathematics: an IMACS journal, 2015, 95, pp.238-249. ⟨10.1016/j.apnum.2014.02.003⟩. ⟨hal-01299247⟩
Journal: Applied Numerical Mathematics: an IMACS journal
I. Thiagalingam, M. Dallet, I. Bennaceur, S. Cadalen, Pierre Sagaut. Exact non local expression for the wall heat transfer coefficient in tubular catalytic reactors. International Journal of Heat and Fluid Flow, 2015, 54, pp.97-106. ⟨10.1016/j.ijheatfluidflow.2015.03.007⟩. ⟨hal-01276484⟩ Plus de détails...
A new exact and non local expression for the wall Nusselt number is derived to have a deep insight into the physical mechanisms that govern the wall heat transfer. 3D high-fidelity numerical simulations (RANS) are then carried out in tubular packed beds and a new set of criteria is defined to extend the Representative Elementary Volume concept to packed bed configurations which enables to unequivocally up-scale 3D simulation data to the observation scale. The mean flow deviation and the mechanical dispersion are shown to play a key role in the wall heat transfer. Finally, the usual correlations of the form View the MathML source Nu=αRepβ found in the literature for the Nusselt number are validated through fine 3D simulations and on the basis of physical investigations for 4000 ⩽ Rep ⩽ 30,000.
I. Thiagalingam, M. Dallet, I. Bennaceur, S. Cadalen, Pierre Sagaut. Exact non local expression for the wall heat transfer coefficient in tubular catalytic reactors. International Journal of Heat and Fluid Flow, 2015, 54, pp.97-106. ⟨10.1016/j.ijheatfluidflow.2015.03.007⟩. ⟨hal-01276484⟩
Journal: International Journal of Heat and Fluid Flow
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, 2015, 55 (7), ⟨10.1088/0029-5515/55/7/073011⟩. ⟨hal-01462144⟩ Plus de détails...
A demonstration power plant (DEMO) will be the next step for fusion energy following ITER. Some of the key design questions can be addressed by simulations using system codes. System codes aim to model the whole plant with all its subsystems and identify the impact of their interactions on the design choices. The SYCOMORE code is a modular system code developed to address key questions relevant to tokamak fusion reactor design. SYCOMORE is being developed within the European Integrated Tokamak Modelling framework and provides a global view (technology and physics) of the plant. It includes modules to address plasma physics, divertor physics, breeding blankets, shield design, magnet design and the power balance of plant. The code is coupled to an optimization framework which allows one to specify figures of merit and constraints to obtain optimized designs. Examples of pulsed and steady-state DEMO designs obtained using SYCOMORE are presented. Sensitivity to design assumptions is also studied, showing that the operational domain around working points can be narrow for some cases.
Cédric Reux, Luc Di Gallo, Frédéric Imbeaux, Jean-François Artaud, P. Bernardi, et al.. DEMO reactor design using the new modular system code SYCOMORE. Nuclear Fusion, 2015, 55 (7), ⟨10.1088/0029-5515/55/7/073011⟩. ⟨hal-01462144⟩
Pierre Magnico. Ion transport dependence on the ion pairing/solvation competition in cation-exchange membranes. Journal of Membrane Science, 2015, 483, pp.112-127. ⟨10.1016/j.memsci.2015.01.051⟩. ⟨hal-01298876⟩ Plus de détails...
Effect of ion-pairing on ion partitioning at equilibrium and on transport properties is studied by means of the Poisson–Nernst–Planck (PNP) equations. Owing to the low electrolyte solution relative permittivity (εSεS) and the high ion density in the membrane, the excess terms of the chemical potential must be computed. In this aim, the density functional theory and the binding mean sphere approximation were used in order to extend the PNP equations and to compute the association constant. The counter-ion/fixed-charge-group pairing and the counter-ion/co-ion one were examined. In the case of monovalent fixed charge, the total density of co-ion and the free one decreases with εSεS owing to the solvation contribution. So that it induces a decrease of the membrane system conductivity. If the counter-ion/co-ion pairing is considered, the free co-ion density and the conductivity increase when εSεS reaches small values. However in the ohmic regime, this dependence of the conductivity towards the free co-ion density is not always fulfilled.
Pierre Magnico. Ion transport dependence on the ion pairing/solvation competition in cation-exchange membranes. Journal of Membrane Science, 2015, 483, pp.112-127. ⟨10.1016/j.memsci.2015.01.051⟩. ⟨hal-01298876⟩
Wouter J.T. Bos, Benjamin Kadoch, Kai Schneider. Angular statistics of Lagrangian trajectories in turbulence. Physical Review Letters, 2015, 114, pp.214502. ⟨10.1103/PhysRevLett.114.214502⟩. ⟨hal-01085070⟩ Plus de détails...
The angle between subsequent particle displacement increments is evaluated as a function of the timelag in isotropic turbulence. It is shown that the evolution of this angle contains two well-defined power-laws, reflecting the multi-scale dynamics of high-Reynolds number turbulence. The proba-bility density function of the directional change is shown to be self-similar and well approximated by an analytically derived model assuming Gaussianity and independence of the velocity and the Lagrangian acceleration.
Wouter J.T. Bos, Benjamin Kadoch, Kai Schneider. Angular statistics of Lagrangian trajectories in turbulence. Physical Review Letters, 2015, 114, pp.214502. ⟨10.1103/PhysRevLett.114.214502⟩. ⟨hal-01085070⟩
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, 2015, 57 (5), pp.054014. ⟨10.1088/0741-3335/57/5/054014⟩. ⟨hal-01299732⟩ Plus de détails...
The 3D global edge turbulence code TOKAM3X is used to study the properties of edge particle turbulent transport in circular limited plasmas, including both closed and open flux surfaces. Turbulence is driven by an incoming particle flux from the core plasma and no scale separation between the equilibrium and the fluctuations is assumed. Simulations show the existence of a complex self-organization of turbulence transport coupling scales ranging from a few Larmor radii up to the machine scale. Particle transport is largely dominated by small scale turbulence with fluctuations forming quasi field-aligned filaments. Radial particle transport is intermittent and associated with the propagation of coherent structures on long distances via avalanches. Long range correlations are also found in the poloidal and toroidal direction. The statistical properties of fluctuations vary with the radial and poloidal directions, with larger fluctuation levels and intermittency found in the outboard scrape-off layer (SOL). Radial turbulent transport is strongly ballooned, with 90% of the flux at the separatrix flowing through the low-field side. One of the main consequences is the existence of quasi-sonic asymmetric parallel flows driving a net rotation of the plasma. Simulations also show the spontaneous onset of an intermittent E × B rotation characterized by a larger shear at the separatrix. Strong correlation is found between the turbulent particle flux and the E × B flow shear in a phenomenology reminiscent of H-mode physics. The poloidal position of the limiter is a key player in the observed dynamics.
Patrick Tamain, Philippe Ghendrih, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, et al.. Multi-scale self-organisation of edge plasma turbulent transport in 3D global simulations. Plasma Physics and Controlled Fusion, 2015, 57 (5), pp.054014. ⟨10.1088/0741-3335/57/5/054014⟩. ⟨hal-01299732⟩
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michael Le Bars. Velocity and temperature measurements in a turbulent water-filled Taylor–Couette–Poiseuille system. International Journal of Thermal Sciences, 2015, 90, pp.238-247. ⟨10.1016/j.ijthermalsci.2014.12.018⟩. ⟨hal-01308638⟩ Plus de détails...
Motivated by the difficulties encountered by engineers to cool down the rotating shafts of industrial machines, the present work investigates the heat and mass transfers in the rotor-stator gap of a Taylor–Couette system with an axial water flow characterized by an aspect ratio Γ = 50 and a radius ratio η = 8/9. Extensive velocity and temperature measurements have been performed on an experimental set-up for a wide range of the flow parameters: the axial Reynolds number Re and the Taylor number Ta reach the values 1.12 × 104 and 7.9 × 107 respectively. In particular, coherent structures close to the rotating wall were measured by Stereo Particle Image Velocimetry. A correlation for the Nusselt number Nu on the rotating wall is finally provided against the axial Reynolds, Taylor and Prandtl numbers. Nu is proportional to the Taylor number to the power ∼0.13 close to the exponent 1/7 highlighted by an analytical model. This small exponent traduces the control of heat transfers by the rotating viscous layer and thus may explain the difficulty met by engineers to develop strategies for the effective cooling of such rotating apparatus.
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michael Le Bars. Velocity and temperature measurements in a turbulent water-filled Taylor–Couette–Poiseuille system. International Journal of Thermal Sciences, 2015, 90, pp.238-247. ⟨10.1016/j.ijthermalsci.2014.12.018⟩. ⟨hal-01308638⟩
Journal: International Journal of Thermal Sciences
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David C. Montgomery. Magnetohydrodynamically generated velocities in confined plasma. Physics of Plasmas, 2015, 22 (4), pp.042515. ⟨10.1063/1.4918774⟩. ⟨hal-00849742⟩ Plus de détails...
We investigate by numerical simulation the rotational flows in a toroid confining a conducting magnetofluid in which a current is driven by the application of externally supported electric and magnetic fields. The computation involves no microscopic instabilities and is purely magnetohydrodynamic (MHD). We show how the properties and intensity of the rotations are regulated by dimensionless numbers (Lundquist and viscous Lundquist) that contain the resistivity and viscosity of the magnetofluid. At the magnetohydrodynamic level (uniform mass density and incompressible magnetofluids), rotational flows appear in toroidal, driven MHD. The evolution of these flows with the transport coefficients, geometry, and safety factor are described.
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David C. Montgomery. Magnetohydrodynamically generated velocities in confined plasma. Physics of Plasmas, 2015, 22 (4), pp.042515. ⟨10.1063/1.4918774⟩. ⟨hal-00849742⟩
Olivier Roussel, Kai Schneider. Adaptive multiresolution computations applied to detonations. Zeitschrift für Physikalische Chemie, 2015, 229 (6), pp.931-953. ⟨hal-01118153⟩ Plus de détails...
A space-time adaptive method is presented for the reactive Euler equations describing chemically reacting gas flow where a two species model is used for the chemistry. The governing equations are discretized with a finite volume method and dynamic space adaptivity is introduced using multiresolution analysis. A time splitting method of Strang is applied to be able to consider stiff problems while keeping the method explicit. For time adaptivity an improved Runge--Kutta--Fehlberg scheme is used. Applications deal with detonation problems in one and two space dimensions. A comparison of the adaptive scheme with reference computations on a regular grid allow to assess the accuracy and the computational efficiency, in terms of CPU time and memory requirements.
Olivier Roussel, Kai Schneider. Adaptive multiresolution computations applied to detonations. Zeitschrift für Physikalische Chemie, 2015, 229 (6), pp.931-953. ⟨hal-01118153⟩
Seyed Amin Ghaffari, Stéphane Viazzo, Kai Schneider, Patrick Bontoux. Simulation of forced deformable bodies interacting with two-dimensional incompressible flows: Application to fish-like swimming. International Journal of Heat and Fluid Flow, 2015, Theme special issue celebrating the 75th birthdays of Brian Launder and Kemo Hanjalic, 51, pp.88-109. ⟨10.1016/j.ijheatfluidflow.2014.10.023⟩. ⟨hal-00967077v2⟩ Plus de détails...
We present an efficient algorithm for simulation of deformable bodies interacting with two-dimensional incompressible flows. The temporal and spatial discretizations of the Navier-Stokes equations in vorticity stream-function formulation are based on classical fourth-order Runge-Kutta and compact finite differences, respectively. Using a uniform Cartesian grid we benefit from the advantage of a new fourth-order direct solver for the Poisson equation to ensure the incompressibility constraint down to machine zero. For introducing a deformable body in fluid flow, the volume penalization method is used. A Lagrangian structured grid with prescribed motion covers the deformable body interacting with the surrounding fluid due to the hydrodynamic forces and moment calculated on the Eulerian reference grid. An efficient law for curvature control of an anguilliform fish, swimming to a prescribed goal, is proposed. Validation of the developed method shows the efficiency and expected accuracy of the algorithm for fish-like swimming and also for a variety of fluid/solid interaction problems.
Seyed Amin Ghaffari, Stéphane Viazzo, Kai Schneider, Patrick Bontoux. Simulation of forced deformable bodies interacting with two-dimensional incompressible flows: Application to fish-like swimming. International Journal of Heat and Fluid Flow, 2015, Theme special issue celebrating the 75th birthdays of Brian Launder and Kemo Hanjalic, 51, pp.88-109. ⟨10.1016/j.ijheatfluidflow.2014.10.023⟩. ⟨hal-00967077v2⟩
Journal: International Journal of Heat and Fluid Flow
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Suction/Injection Effects on the Swirling Flow of a Reiner-Rivlin Fluid near a Rough Surface. Hindawi Publishing Corporation, 2015, 2015, Article ID 253504, 5 p. ⟨10.1155/2015/253504⟩. ⟨hal-01100098⟩ Plus de détails...
The similarity equations for the Bödewadt flow of a non-Newtonian Reiner-Rivlin fluid, subject to uniform suction/injection, are solved numerically. The conventional no-slip boundary conditions are replaced by corresponding partial slip boundary conditions, owing to the roughness of the infinite stationary disk. The combined effects of surface slip, suction/injection velocity, and cross-viscous parameter on the momentum boundary layer are studied in detail. It is interesting to find that suction dominates the oscillations in the velocity profiles and decreases the boundary layer thickness significantly. On the other hand, injection has opposite effects on the velocity profiles and the boundary layer thickness.
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Suction/Injection Effects on the Swirling Flow of a Reiner-Rivlin Fluid near a Rough Surface. Hindawi Publishing Corporation, 2015, 2015, Article ID 253504, 5 p. ⟨10.1155/2015/253504⟩. ⟨hal-01100098⟩
Pedro Valero-Lara, Francisco D. Igual, Manuel Prieto-Matías, Alfredo Pinelli, Julien Favier. Accelerating fluid–solid simulations (Lattice-Boltzmann & Immersed-Boundary) on heterogeneous architectures. Journal of computational science, 2015, 10, pp.249-261. ⟨10.1016/j.jocs.2015.07.002⟩. ⟨hal-01225734⟩ Plus de détails...
We propose a numerical approach based on the Lattice-Boltzmann (LBM) and Immersed Boundary (IB) methods to tackle the problem of the interaction of solids with an incompressible fluid flow, and its implementation on heterogeneous platforms based on data-parallel accelerators such as NVIDIA GPUs and the Intel Xeon Phi. We explain in detail the parallelization of these methods and describe a number of optimizations, mainly focusing on improving memory management and reducing the cost of host-accelerator communication. As previous research has consistently shown, pure LBM simulations are able to achieve good performance results on heterogeneous systems thanks to the high parallel efficiency of this method. Unfortunately, when coupling LBM and IB methods, the overheads of IB degrade the overall performance. As an alternative, we have explored different hybrid implementations that effectively hide such overheads and allow us to exploit both the multi-core and the hardware accelerator in a cooperative way, with excellent performance results.
Pedro Valero-Lara, Francisco D. Igual, Manuel Prieto-Matías, Alfredo Pinelli, Julien Favier. Accelerating fluid–solid simulations (Lattice-Boltzmann & Immersed-Boundary) on heterogeneous architectures. Journal of computational science, 2015, 10, pp.249-261. ⟨10.1016/j.jocs.2015.07.002⟩. ⟨hal-01225734⟩
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Numerical simulation of fluid–structure interaction with the volume penalization method. Journal of Computational Physics, 2015, 281, pp.96-115. ⟨10.1016/j.jcp.2014.10.005⟩. ⟨hal-01299253⟩ Plus de détails...
We present a novel scheme for the numerical simulation of fluid–structure interaction problems. It extends the volume penalization method, a member of the family of immersed boundary methods, to take into account flexible obstacles. We show how the introduction of a smoothing layer, physically interpreted as surface roughness, allows for arbitrary motion of the deformable obstacle. The approach is carefully validated and good agreement with various results in the literature is found. A simple one-dimensional solid model is derived, capable of modeling arbitrarily large deformations and imposed motion at the leading edge, as it is required for the simulation of simplified models for insect flight. The model error is shown to be small, while the one-dimensional character of the model features a reasonably easy implementation. The coupled fluid–solid interaction solver is shown not to introduce artificial energy in the numerical coupling, and validated using a widely used benchmark. We conclude with the application of our method to models for insect flight and study the propulsive efficiency of one and two wing sections.
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Numerical simulation of fluid–structure interaction with the volume penalization method. Journal of Computational Physics, 2015, 281, pp.96-115. ⟨10.1016/j.jcp.2014.10.005⟩. ⟨hal-01299253⟩
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, 2015, 463, pp.489-492. ⟨10.1016/j.jnucmat.2014.10.079⟩. ⟨hal-01225211⟩ Plus de détails...
To understand the mechanisms behind poloidal asymmetries of the transport in the edge and SOL plasma, it is important to take into account drift velocity in the transport model. We investigate the effects of an imposed radial electric field on the plasma equilibrium in the transport code SOLEDGE2D. In the edge, we show an important modification of the flow pattern due to poloidal E × B drift velocity. The drift velocity generates asymmetry of the density through the Pfirsch–Schluter flows which creates an important parallel rotation through the viscous balance. In comparison to heat load imbalance studies in the SOL of divertor tokamak, a strong link between the amplitude of the radial electric field and the heat load imbalance in the SOL of limiter tokamak has been highlighted using different amplitude of the imposed radial electric field.
R. Leybros, Hugo Bufferand, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Investigation of drift velocity effects on the EDGE and SOL transport. Journal of Nuclear Materials, 2015, 463, pp.489-492. ⟨10.1016/j.jnucmat.2014.10.079⟩. ⟨hal-01225211⟩
Christophe Friess, Remi Manceau, T.B. Gatski. Toward an equivalence criterion for Hybrid RANS/LES methods. Computers and Fluids, 2015, 122, pp.233-246. ⟨10.1016/j.compfluid.2015.08.010⟩. ⟨hal-01246130⟩ Plus de détails...
A criterion is established to assess the equivalence between hybrid RANS/LES methods, called H-equivalence, based on the modeled energy of the unresolved scales, which leads to similar low-order statistics of the resolved motion. Different equilibrium conditions are considered, and perturbation analyses about the equilibrium states are performed. The procedure is applied to demonstrate the equivalence between two particular hybrid methods, and leads to relationships between hybrid method parameters that control the partitioning of energy between the resolved and unresolved scales of motion. This equivalence is validated by numerical results obtained for the cases of plane and periodically constricted channel flows. This concept of H-equivalence makes it possible to view different hybrid methods as models for the same system of equations: as a consequence, detached-eddy simulation (DES), which is shown to be H-equivalent to the temporal partially integrated transport model (T-PITM) in inhomogeneous, stationary situations, can be interpreted as a model for the subfilter stress involved in the temporally filtered Navier–Stokes equations.
Christophe Friess, Remi Manceau, T.B. Gatski. Toward an equivalence criterion for Hybrid RANS/LES methods. Computers and Fluids, 2015, 122, pp.233-246. ⟨10.1016/j.compfluid.2015.08.010⟩. ⟨hal-01246130⟩
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, 2015, 463, pp.654-658. ⟨10.1016/j.jnucmat.2015.01.019⟩. ⟨hal-01225200⟩ Plus de détails...
A 3D global turbulence fluid code, TOKAM3X is used to investigate the effect of the limiter position on the edge plasma parallel flows and density profiles. Six configurations with different poloidal contact points in the machine are considered. For each one, asymmetric quasi-sonic parallel flows are found, owing to the ballooning of radial turbulent transport around the LFS mid-plane. In spite of the relative simplicity of the model used (isothermal, sheat-limited, no recycling), simulations exhibit trends in-line with experimental findings. Reversal of the flows is found when the limiter is moved from −30° under to 30° above the outboard mid-plane. The SOL width varies with the poloidal location and depends notably on the poloidal position of the limiter. Turbulence itself is shown to be impacted by the position of the limiter, radial transport appearing less ballooned with a LFS limiter than with a HFS.
Clothilde Colin, Patrick Tamain, Frederic Schwander, Eric Serre, Hugo Bufferand, et al.. Impact of the plasma-wall contact position on edge turbulent transport and poloidal asymmetries in 3D global turbulence simulations. Journal of Nuclear Materials, 2015, 463, pp.654-658. ⟨10.1016/j.jnucmat.2015.01.019⟩. ⟨hal-01225200⟩
Nabila Ait-Moussa, Sébastien Poncet, Abdelrahmane Ghezal. Numerical Simulations of Co- and Counter-Taylor-Couette Flows: Influence of the Cavity Radius Ratio on the Appearance of Taylor Vortices. American Journal of Fluid Dynamics, 2015, 5 (1), pp.17-22. ⟨10.5923/j.ajfd.20150501.02⟩. ⟨hal-01300130⟩ Plus de détails...
Taylor-Couette flows in the annular region between rotating concentric cylinders are studied numerically to determine the combined effects of the co- and counter-rotation of the outer cylinder and the radius ratio on the system response. The computational procedure is based on a finite volume method using staggered grids. The axisymmetric conservative governing equations are solved using the SIMPLER algorithm. One considers the flow confined in a finite cavity with radius ratios η = 0.25, 0.5, 0.8 and 0.97. One has determined the critical points and properties for the bifurcation from the basic circular Couette flow (CCF) to the Taylor Vortex Flow (TVF) state. Indeed, the results are presented in terms of the critical Reynolds number Rei of the inner cylinder that depends on the rotational Reynolds number of the outer cylinder Reo and η. To show the capability of the present code, excellent quantitative agreement has been obtained between the calculations and previous experimental measurements for a wide range of radius ratios and rotation rates.
Nabila Ait-Moussa, Sébastien Poncet, Abdelrahmane Ghezal. Numerical Simulations of Co- and Counter-Taylor-Couette Flows: Influence of the Cavity Radius Ratio on the Appearance of Taylor Vortices. American Journal of Fluid Dynamics, 2015, 5 (1), pp.17-22. ⟨10.5923/j.ajfd.20150501.02⟩. ⟨hal-01300130⟩
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulent
statistics analysis. International Journal of Heat and Fluid Flow, 2015, 51, pp.65-77. ⟨hal-01138803⟩ Plus de détails...
This study analyses the mixing and thermal fluctuations induced in a mixing tee junction with circular cross-sections when cold water flowing in a pipe is joined by hot water from a branch pipe. This config- uration is representative of industrial piping systems in which temperature fluctuations in the fluid may cause thermal fatigue damage on the walls. Implicit large-eddy simulations (LES) are performed for equal inflow rates corresponding to a bulk Reynolds number Re= 39,080. Two different thermal boundary conditions are studied for the pipe walls; an insulating adiabatic boundary and a conducting steel wall boundary. The predicted flow structures show a satisfactory agreement with the literature. The velocity and thermal fields (including high-order statistics) are not affected by the heat transfer with the steel walls. However, predicted thermal fluctuations at the boundary are not the same between the flow and the solid, showing that solid thermal fluctuations cannot be predicted by the knowledge of the fluid thermal fluctuations alone. The analysis of high-order turbulent statistics provides a better understand- ing of the turbulence features. In particular, the budgets of the turbulent kinetic energy and temperature variance allows a comparative analysis of dissipation, production and transport terms. It is found that the turbulent transport term is an important term that acts to balance the production. We therefore use a priori tests to evaluate three different models for the triple correlation
Richard Howard, Eric Serre. Large-eddy simulation in a mixing tee junction: High-order turbulent
statistics analysis. International Journal of Heat and Fluid Flow, 2015, 51, pp.65-77. ⟨hal-01138803⟩
Journal: International Journal of Heat and Fluid Flow
Julien Favier, Alistair Revell, Alfredo Pinelli. Numerical study of flapping filaments in a uniform fluid flow. Journal of Fluids and Structures, 2015, 53, pp.26-35. ⟨10.1016/j.jfluidstructs.2014.11.010⟩. ⟨hal-01118360⟩ Plus de détails...
The coupled dynamics of multiple flexible filaments (also called monodimen-sional flags) flapping in a uniform fluid flow is studied numerically for the cases of a side-by-side arrangement, and an in-line configuration. The modal behaviour and hydrodynamical properties of the sets of filaments are studied using a Lattice Boltzmann-Immersed Boundary method. The fluid momentum equations are solved on a Cartesian uniform lattice while the beating filaments are tracked through a series of markers, whose dynamics are functions of the forces exerted by the fluid, the filaments flexural rigidity and the tension. The instantaneous wall conditions on the filaments are imposed via a system of singular body forces, consistently discretised on the lattice of the Boltzmann equation. The results exhibits several flapping modes for two and three filaments placed side-by-side and are compared with experimental and theoretical studies. The hydrodynamical drafting, observed so far only experimentally on configurations of in-line flexible bodies, is also revisited numerically in this work, and the associated physical mechanism is identified. In certain geometrical and structural configuration, it is found that the upstream body experiences a reduced drag compared to the downstream body, which is the contrary of what is encountered on rigid bodies (cars, bicycles).
Julien Favier, Alistair Revell, Alfredo Pinelli. Numerical study of flapping filaments in a uniform fluid flow. Journal of Fluids and Structures, 2015, 53, pp.26-35. ⟨10.1016/j.jfluidstructs.2014.11.010⟩. ⟨hal-01118360⟩
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, 2015, 463, pp.420-423. ⟨10.1016/j.jnucmat.2014.09.061⟩. ⟨hal-01225205⟩ Plus de détails...
The influence of the plasma facing components material on the scrape-off layer plasma is investigated. In particular, the energy recycling is found to be more pronounced for tungsten wall compared with carbon wall. Edge plasma simulations performed with the transport code SOLEDGE2D-EIRENE show that this enhanced energy recycling in the tungsten case leads to an increase of the scrape-off layer temperature. Moreover, the energy recycling depends on the ion angle of incidence with the wall. A PIC code has been used to model the ion acceleration in the magnetic pre-sheath and determine the later angle of incidence. These simulations show that ions mostly impact the wall with rather shallow incident angles leading to a further increase of the energy recycling.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, P. Genesio, et al.. Comparison on heat flux deposition between carbon and tungsten wall – Investigations on energy recycling. Journal of Nuclear Materials, 2015, 463, pp.420-423. ⟨10.1016/j.jnucmat.2014.09.061⟩. ⟨hal-01225205⟩
Marie Farge, Kai Schneider. Wavelet transforms and their applications to MHD and plasma turbulence: a review. Journal of Plasma Physics, 2015, 81 (06), pp.435810602. ⟨10.1017/S0022377815001075⟩. ⟨hal-01299264⟩ Plus de détails...
Wavelet analysis and compression tools are reviewed and different applications to study MHD and plasma turbulence are presented. We introduce the continuous and the orthogonal wavelet transform and detail several statistical diagnostics based on the wavelet coefficients. We then show how to extract coherent structures out of fully developed turbulent flows using wavelet-based denoising. Finally some multiscale numerical simulation schemes using wavelets are described. Several examples for analyzing, compressing and computing one, two and three dimensional turbulent MHD or plasma flows are presented.
Marie Farge, Kai Schneider. Wavelet transforms and their applications to MHD and plasma turbulence: a review. Journal of Plasma Physics, 2015, 81 (06), pp.435810602. ⟨10.1017/S0022377815001075⟩. ⟨hal-01299264⟩
S-G Cai, A Ouahsine, H Smaoui, Julien Favier, Yannis Hoarau. An efficient implicit direct forcing immersed boundary method for incompressible flows. Journal of Physics: Conference Series, 2015, 574 (012165), pp.5. ⟨10.1088/1742-6596/574/1/012165⟩. ⟨hal-01225703⟩ Plus de détails...
A novel efficient implicit direct forcing immersed boundary method for incompressible flows with complex boundaries is presented. In the previous work [1], the calculation is performed on the Cartesian grid regardless of the immersed object, with a fictitious force evaluated on the Lagrangian points to mimic the presence of the physical boundaries. However the explicit direct forcing method [1] fails to accurately impose the non-slip boundary condition on the immersed interface. In the present work, the calculation is based on the implicit treatment of the artificial force while in an effective way of system iteration. The accuracy is also improved by solving the Navier-Stokes equation with the rotational incremental pressure- correction projection method of Guermond and Shen [2]. Numerical simulations performed with the proposed method are in good agreement with those in the literature.
S-G Cai, A Ouahsine, H Smaoui, Julien Favier, Yannis Hoarau. An efficient implicit direct forcing immersed boundary method for incompressible flows. Journal of Physics: Conference Series, 2015, 574 (012165), pp.5. ⟨10.1088/1742-6596/574/1/012165⟩. ⟨hal-01225703⟩
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, 2015, 55 (5), pp.053025. ⟨hal-01225195⟩ Plus de détails...
In the perspective of operating tungsten monoblocks in WEST, the ongoing major upgrade of the Tore Supra tokamak, a dedicated modelling effort has been carried out to simulate the interaction between the edge plasma and the tungsten wall. A new transport code, SolEdge2D–EIRENE, has been developed with the ability to simulate the plasma up to the first wall. This is especially important for steady state operation, where thermal loads on all the plasma facing components, even remote from the plasma, are of interest. Moreover, main chamber tungsten sources are thought to dominate the contamination of the plasma core. We present here in particular new developments aimed at improving the description of the interface between the plasma and the wall, namely a way to treat sheath physics in a more faithful way using the output of 1D particle in cell simulations. Moreover, different models for prompt redeposition have been implemented and are compared. The latter is shown to play an important role in the balance between divertor and main chamber sources.
Hugo Bufferand, Guido Ciraolo, Yannick Marandet, Jérome Bucalossi, Philippe Ghendrih, et al.. Numerical modelling for divertor design of the WEST device with a focus on plasma–wall interactions. Nuclear Fusion, 2015, 55 (5), pp.053025. ⟨hal-01225195⟩
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Effects of slip on the Von Kármán swirling flow and heat transfer in a porous medium. Transactions of the Canadian Society for Mechanical Engineering, 2015, 39 (2), pp.357-366. ⟨10.1139/tcsme-2015-0025⟩. ⟨hal-01300117⟩ Plus de détails...
Numerical solutions are obtained for the fully coupled and highly nonlinear system of differential equations, arising due to the steady Kármán flow and heat transfer of a viscous fluid in a porous medium. The conventional no-slip boundary conditions are replaced by partial slip boundary conditions owing to the roughness of the disk surface. Combined effects of the slip λ and porosity γ parameters on the momentum and thermal boundary layers are studied in detail. Both parameters produce the same effects on the mean velocity profiles, such that all velocity components are reduced by increasing either λ or γ. The temperature slip factor β has a dominating influence on the temperature profiles by decreasing the fluid temperature in the whole domain. The porosity parameter strongly decreases the heat transfer coefficient at the wall for low values of β and tends to an asymptotical limit around 0.1 for β 10. The porosity parameter γ increases the moment coefficient at the disk surface, which is found to monotonically decrease with λ .
Bikash Sahoo, Sébastien Poncet, Fotini Labropulu. Effects of slip on the Von Kármán swirling flow and heat transfer in a porous medium. Transactions of the Canadian Society for Mechanical Engineering, 2015, 39 (2), pp.357-366. ⟨10.1139/tcsme-2015-0025⟩. ⟨hal-01300117⟩
Journal: Transactions of the Canadian Society for Mechanical Engineering
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michel Lebars. Velocity and temperature measurements in a turbulent water-filled Taylor-Couette-Poiseuille system. International Journal of Thermal Sciences, 2015. ⟨hal-01467719⟩ Plus de détails...
Motivated by the difficulties encountered by engineers to cool down the rotating shafts of industrial machines, the present work investigates the heat and mass transfers in the rotor-stator gap of a Taylor–Couette system with an axial water flow characterized by an aspect ratio Γ = 50 and a radius ratio η = 8/9. Extensive velocity and temperature measurements have been performed on an experimental set-up for a wide range of the flow parameters: the axial Reynolds number Re and the Taylor number Ta reach the values 1.12 × 104 and 7.9 × 107 respectively. In particular, coherent structures close to the rotating wall were measured by Stereo Particle Image Velocimetry. A correlation for the Nusselt number Nu on the rotating wall is finally provided against the axial Reynolds, Taylor and Prandtl numbers. Nu is proportional to the Taylor number to the power ∼0.13 close to the exponent 1/7 highlighted by an analytical model. This small exponent traduces the control of heat transfers by the rotating viscous layer and thus may explain the difficulty met by engineers to develop strategies for the effective cooling of such rotating apparatus.
Adrien Aubert, Sébastien Poncet, Patrice Le Gal, Stéphane Viazzo, Michel Lebars. Velocity and temperature measurements in a turbulent water-filled Taylor-Couette-Poiseuille system. International Journal of Thermal Sciences, 2015. ⟨hal-01467719⟩
Journal: International Journal of Thermal Sciences
Francisco Toja-Silva, Julien Favier, Alfredo Pinelli. Radial Basis Function (RBF)-based Interpolation and Spreading for the Immersed Boundary Method. Computers and Fluids, 2014, 105, pp.66-75. ⟨10.1016/j.compfluid.2014.09.026⟩. ⟨hal-01069809⟩ Plus de détails...
Immersed boundary methods are efficient tools of growing interest as they allow to use generic CFD codes to deal with complex, moving and deformable geometries, for a reasonable computational cost compared to classical body- conformal or unstructured mesh approaches. In this work, we propose a new immersed boundary method based on a radial basis functions frame- work for the spreading-interpolation procedure. The radial basis function approach allows for dealing with a cloud of scattered nodes around the im- mersed boundary, thus enabling the application of the devised algorithm to any underlying mesh system. The proposed method can also keep into ac- count both Dirichlet and Neumann type conditions. To demonstrate the capabilities of our novel approach, the imposition of Dirichlet boundary con- ditions on a 2D cylinder geometry in a Navier-Stokes CFD solver, and the imposition of Neumann boundary conditions on an adiabatic wall in an un- steady heat conduction problem are considered. One of the most significant advantage of the proposed method lies in its simplicity given by the algo- rithmic possibility of carrying out the interpolation and spreading steps all together, in a single step.
Francisco Toja-Silva, Julien Favier, Alfredo Pinelli. Radial Basis Function (RBF)-based Interpolation and Spreading for the Immersed Boundary Method. Computers and Fluids, 2014, 105, pp.66-75. ⟨10.1016/j.compfluid.2014.09.026⟩. ⟨hal-01069809⟩
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. ⟨10.1088/1742-6596/561/1/012009⟩. ⟨hal-01100365⟩ Plus de détails...
In the scrape-off layer (SOL) of tokamaks, the flow acceleration due to the presence of limiter or divertor plates rises the plasma velocity in a sonic regime. These high velocities imply the presence of a strong shear between the SOL and the core of the plasma that can possibly trigger some parallel shear flow instability. The existence of these instabilities, denoted as parallel Kelvin-Helmholtz instability in some works [1, 2] have been investigated theoretically in [3] using a minimal model of electrostatic turbulence composed of a mass density and parallel velocity equations. This work showed that the edge plasma around limiters might indeed be unstable to this type of parallel shear flow instabilities. In this work, we perform 3D simulations of the same simple mathematical model to validate an original finite volume numerical method aimed to the numerical study of edge plasma. This method combines the use of triangular unstructured meshes in the poloidal section and structured meshes in the toroidal direction and is particularly suited to the representation of the real complex geometry of the vacuum chamber of a tokamak. The numerical results confirm that in agreement with the theoretical expectations as well as with other numerical methods, the sheared flows in the SOL are subject to parallel Kelvin-Helmholtz instabilities. However, the growth rate of these instabilities is low and these computations require both a sufficient spatial resolution and a long simulation time. This makes the simulation of parallel Kelvin-Helmholtz instabilities a demanding benchmark.
H Guillard, M Bilanceri, C Colin, Philippe Ghendrih, G Giorgiani, et al.. Parallel Kelvin-Helmholtz instability in edge plasma. Journal of Physics: Conference Series, 2014, Joint Varenna-Lausanne International Workshop 2014, 561, pp.012009. ⟨10.1088/1742-6596/561/1/012009⟩. ⟨hal-01100365⟩
The dynamics of a magnetically forced conducting fluid in confined geometries is studied. A pseudospectral method with volume penalisation is used to solve the resistive magnetohydrodynamic (MHD) equations. A helical magnetic field is imposed via boundary conditions, which generates a response in the velocity field for large enough magnitudes. Different helical structures are observed in the flow depending on the magnitude and direction of the forcing and the cross-sectional geometry of the fluid domain. A computational technique for finding a solenoidal vector field which can be used in complex geometries is also proposed.
Sébastien Poncet, Stéphane Viazzo, Oguic Romain. Large eddy simulations of Taylor-Couette-Poiseuille flows in a narrow-gap system. Physics of Fluids, 2014, 26 (10), pp.105108. ⟨10.1063/1.4899196⟩. ⟨hal-01083052⟩ Plus de détails...
The present paper concerns Large-Eddy Simulations (LES) of turbulent Taylor-Couette-Poiseuille flows in a narrow-gap cavity for six different combinations of rotational and axial Reynolds numbers. The in-house numerical code has been first validated in a middle-gap cavity. Two sets of refined LES results, using the Wall-Adapting Local EddyViscosity(WALE) and theDynamic Smagorinsky subgrid-scale models availablewithin an in-house code based on high-order compact schemes, have been then compared with no noticeable difference on the mean flow field and theturbulent statistics. The WALE model enabling a saving of about 12% of computational effort has been finally used to investigate the influence on the hydrodynamics of the swirl parameter N within the range [1.49 − 6.71]. The swirl parameter N, which compares the effects of rotation of the inner cylinder and the axial flowrate, does not influence significantly the mean velocity profiles. Turbulence intensities are enhanced with increasing values of N with remarkably high peak values within the boundary layers. The inner rotating cylinder has a destabilizing effect inducing asymmetric profiles of the Reynolds stress tensor components. The rotor and stator boundary layers exhibit the main characteristics of two-dimensional boundary layers.Turbulence is also mainly at two-component there. Thin coherent structures appearing as negative (resp. positive) spiral rolls are observed along the rotor (resp. stator) side. Their inclination angle depends strongly on the value of the swirl parameter, which fixes the intensity of the crossflow. On the other hand, the intensity and the size of the coherent structures observed within the boundary layers are governed by the effective Reynolds number. For its highest value, they penetrate the whole gap. Finally, the results have been extended to the non-isothermal case in the forced convection regime. A correlation for the Nusselt number along the rotor has been provided showing a much larger dependence on the axial Reynolds number thanexpected from previous published works, while it depends classically on the Taylor number to the power 0.145 and on the Prandtl number to the power 0.3.
Sébastien Poncet, Stéphane Viazzo, Oguic Romain. Large eddy simulations of Taylor-Couette-Poiseuille flows in a narrow-gap system. Physics of Fluids, 2014, 26 (10), pp.105108. ⟨10.1063/1.4899196⟩. ⟨hal-01083052⟩
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, 2014, 26 (9), pp.094102. ⟨10.1063/1.4895400⟩. ⟨hal-01300402⟩ Plus de détails...
Building on the weakly nonlinear amplitude equation of the saturated Taylor vortices developing in a Taylor–Couette cell with a rotating inner cylinder and a fixed outer one, the physical mechanism underlying the destabilization of these vortices resulting in azimuthal waviness is addressed using Floquet analysis. For narrow gap configurations, analysis and direct numerical simulations together with existing experimental results support the idea that the waviness is generated by the axial shear in the azimuthal velocity due to the alternate advection by the Taylor vortices of azimuthal momentum between the cylinders. For wide gap configurations, this mechanism is no longer able to drive the azimuthal waviness and a different mechanism tends to select a subharmonic instability.
Denis Martinand, Eric Serre, Richard M. Lueptow. Mechanisms for the transition to waviness for Taylor vortices. Physics of Fluids, 2014, 26 (9), pp.094102. ⟨10.1063/1.4895400⟩. ⟨hal-01300402⟩
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David Montgomery. The effect of toroidicity on Reversed Field Pinch dynamics. Plasma Physics and Controlled Fusion, 2014, 56, pp.095024 ⟨10.1088/0741-3335/56/9/095024⟩. ⟨hal-01026354⟩ Plus de détails...
The influence of the curvature of the imposed magnetic field on Reversed Field Pinch dynamics is investigated by comparing the flow of a magnetofluid in a torus with aspect ratio 1.83, with the flow in a periodic cylinder. It is found that an axisymmetric toroidal mode is always present in the toroidal, but absent in the cylindrical configuration. In particular, in contrast to the cylinder, the toroidal case presents a double poloidal recirculation cell with a shear localized at the plasma edge. Quasi-single-helicity states are found to be more persistent in toroidal than in periodic cylinder geometry.
Jorge A. Morales, Wouter J.T. Bos, Kai Schneider, David Montgomery. The effect of toroidicity on Reversed Field Pinch dynamics. Plasma Physics and Controlled Fusion, 2014, 56, pp.095024 ⟨10.1088/0741-3335/56/9/095024⟩. ⟨hal-01026354⟩
Giorgio Giorgiani, Sonia Fernández-Méndez, Antonio Huerta. Hybridizable Discontinuous Galerkin with degree adaptivity for the incompressible Navier-Stokes equations ✩. Computers and Fluids, 2014. ⟨hal-01717504⟩ Plus de détails...
A degree adaptive Hybridizable Discontinuous Galerkin (HDG) method for the solution of the incompressible Navier-Stokes equations is presented. The key ingredient is an accurate and computationally inexpensive a posteriori error estimator based on the super-convergence properties of HDG. The error estimator drives the local modification of approximation degree in the elements and faces of the mesh, aimed at obtaining a uniform error distribution below a user-given tolerance in a given are of interest. Three 2D numerical examples are presented. High efficiency of the proposed error estimator is found, and an important reduction of the computational effort is shown with respect to non-adaptive computations, both for steady state and transient simulations.
Giorgio Giorgiani, Sonia Fernández-Méndez, Antonio Huerta. Hybridizable Discontinuous Galerkin with degree adaptivity for the incompressible Navier-Stokes equations ✩. Computers and Fluids, 2014. ⟨hal-01717504⟩
A. Salhi, Frank G. Jacobitz, Kai Schneider, Claude Cambon. Nonlinear dynamics and anisotropic structure of rotating sheared turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89, pp.013020. ⟨10.1103/PhysRevE.89.013020⟩. ⟨hal-01048730⟩ Plus de détails...
Homogeneous turbulence in rotating shear flows is studied by means of pseudospectral direct numerical simulation and analytical spectral linear theory (SLT). The ratio of the Coriolis parameter to shear rate is varied over a wide range by changing the rotation strength, while a constant moderate shear rate is used to enable significant contributions to the nonlinear interscale energy transfer and to the nonlinear intercomponental redistribution terms. In the destabilized and neutral cases, in the sense of kinetic energy evolution, nonlinearity cannot saturate the growth of the largest scales. It permits the smallest scale to stabilize by a scale-by-scale quasibalance between the nonlinear energy transfer and the dissipation spectrum. In the stabilized cases, the role of rotation is mainly nonlinear, and interacting inertial waves can affect almost all scales as in purely rotating flows. In order to isolate the nonlinear effect of rotation, the two-dimensional manifold with vanishing spanwise wave number is revisited and both two-component spectra and single-point two-dimensional energy components exhibit an important effect of rotation, whereas the SLT as well as the purely two-dimensional nonlinear analysis are unaffected by rotation as stated by the Proudman theorem. The other two-dimensional manifold with vanishing streamwise wave number is analyzed with similar tools because it is essential for any shear flow. Finally, the spectral approach is used to disentangle, in an analytical way, the linear and nonlinear terms in the dynamical equations
A. Salhi, Frank G. Jacobitz, Kai Schneider, Claude Cambon. Nonlinear dynamics and anisotropic structure of rotating sheared turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89, pp.013020. ⟨10.1103/PhysRevE.89.013020⟩. ⟨hal-01048730⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Francois Gallaire, Philippe Meliga, Patrice Laure, Charles N. Baroud. Marangoni induced force on a drop in a Hele Shaw cell. Physics of Fluids, 2014, 26 (6), pp.062105. ⟨10.1063/1.4878095⟩. ⟨hal-01054669⟩ Plus de détails...
We analyse the force balance on a cylindrical drop in a Hele-Shaw cell, subjected to a Marangoni flow caused by a surface tension gradient. Depth-averaged Stokes equations, called Brinkman equations, are introduced and a general closed form solution is obtained. The validity of the averaging procedure is ascertained by considering a linear surface tension gradient acting on a cylindrical flattened drop. The Marangoni-driven flow field and resulting force predicted by the Brinkman model are seen to match well a full three-dimensional direct numerical simulation. A closed form ex-pression of the force acting on the drop is obtained, calculated from contributions due to the normal viscous stress, tangential viscous stress, and pressure fields, integrated on the drop perimeter. This expression is used to predict the force balance when a stationary droplet is submitted to both a carrier flow and a Marangoni flow. We show that previous results in the literature had underestimated by a factor two the Marangoni-induced force.
Francois Gallaire, Philippe Meliga, Patrice Laure, Charles N. Baroud. Marangoni induced force on a drop in a Hele Shaw cell. Physics of Fluids, 2014, 26 (6), pp.062105. ⟨10.1063/1.4878095⟩. ⟨hal-01054669⟩
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Crespo Del Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89 (6), ⟨10.1103/PhysRevE.89.063013⟩. ⟨hal-01464703⟩ Plus de détails...
Rayleigh-Benard convection is investigated in rotating annular cavities ă at a moderate dimensionless rotation rate Omega = 60. The onset of ă convection is in the form of azimuthal traveling waves that set in at ă the sidewalls and at values of the Rayleigh number significantly below ă the value of the onset of convection in an infinitely extended layer. ă The present study addresses the effects of curvature and confinement on ă the onset of sidewall convection by using three-dimensional spectral ă solutions of the Oberbeck-Boussinesq equations. Such solutions ă demonstrate that the curvature of the outer boundary promotes the onset ă of the wall mode, while the opposite curvature of the inner boundary ă tends to delay the onset of the wall mode. An inner sidewall with a ă radius as low as one tenth of its height is sufficient, however, to ă support the onset of a sidewall mode. When radial confinement is ă increased the two independent traveling waves interact and eventually ă merge to form a nearly steady pattern of convection.
Jose Joaquin Sanchez-Alvarez, Eric Serre, Emilia Crespo Del Arco, Friedrich.H Busse. Geometry effects on Rayleigh-Benard convection in rotating annular ă layers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89 (6), ⟨10.1103/PhysRevE.89.063013⟩. ⟨hal-01464703⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
The paper presents a numerical investigation of the leading-edge vortices generated by rotating triangular wings at Reynolds number Re=250. A series of three-dimensional numerical simulations have been carried out using a Fourier pseudo-spectral method with volume penalization. The transition from stable attachment of the leading-edge vortex to periodic vortex shedding is explored, as a function of the wing aspect ratio and the angle of attack. It is found that, in a stable configuration, the spanwise flow in the recirculation bubble past the wing is due to the centrifugal force, incompressibility and viscous stresses. For the flow outside of the bubble, an inviscid model of spanwise flow is presented.
Stéphane Viazzo, Sébastien Poncet. Numerical simulation of the flow stability in a high aspect ratio Taylor–Couette system submitted to a radial temperature gradient. Computers and Fluids, 2014, 101, pp.15-26. ⟨10.1016/j.compfluid.2014.05.025⟩. ⟨hal-01083054⟩ Plus de détails...
From 28 high-order DNS computations, one investigates the formation of instabilities due to the strong competition between an azimuthal flow induced by rotation and an axial flow due to convection in a tall Taylor–Couette apparatus (gamma=80; eta=0.8) submitted to a radial temperature gradient. One explores the richness of the transition diagram that reports seven different flow patterns appearing either as spiral rolls, wavy vortices or a combination of both depending on the Taylor and Rayleigh numbers. The partial spiral regime observed experimentally by Guillerm (2010) is not recovered at very low Rayleigh numbers. The spatio-temporal properties of the different spirals close to the threshold of the primary instability are fairly predicted and a new insight on the flow and thermal structures of the instabilities is gained from this study. Finally, the distributions of the Nusselt number against the Taylor number are established for various Rayleigh numbers.
Stéphane Viazzo, Sébastien Poncet. Numerical simulation of the flow stability in a high aspect ratio Taylor–Couette system submitted to a radial temperature gradient. Computers and Fluids, 2014, 101, pp.15-26. ⟨10.1016/j.compfluid.2014.05.025⟩. ⟨hal-01083054⟩
Sébastien Poncet. The stability of a thin water layer over a rotating disk revisited. The European Physical Journal Plus, 2014, 129, pp.167. ⟨10.1140/epjp/i2014-14167-2⟩. ⟨hal-01083053⟩ Plus de détails...
The flow driven by a rotating disk of a thin fluid layer in a fixed cylindrical casing is studied by direct numerical simulation and experimental flow visualizations. The characteristics of the flow are first briefly discussed but the focus of this work is to understand the transition to the primary instability. The primary bifurcation is 3D and appears as spectacular sharp-cornered polygonal patterns located along the shroud. The stability diagram is established experimentally in a (Re, G) plane, where G is the aspect ratio of the cavity and Re the rotational Reynolds number and confirmed numerically. The number of vortices scales well with the Ekman number based on the water depth, which confirms the existence of a Stewartsonlayer along the external cylinder. The critical mixed Reynolds number is found to be constant as in other rotating flows involving a shear-layer instability. Hysteresis cycles are observed highlighting the importance of the spin-up and spin-down processes. In some particular cases, a crossflow instability appears under the form of high azimuthal wave number spiral patterns, similar to those observed in a rotor-stator cavity with throughflow and coexists with the polygons. The DNS calculations confirm the experimental results under the flat free surface hypothesis.
Sébastien Poncet. The stability of a thin water layer over a rotating disk revisited. The European Physical Journal Plus, 2014, 129, pp.167. ⟨10.1140/epjp/i2014-14167-2⟩. ⟨hal-01083053⟩
Romain Nguyen van Yen, Dmitry Kolomenskiy, Kai Schneider. Approximation of the Laplace and Stokes operators with Dirichlet boundary conditions through volume penalization: a spectral viewpoint. Numerische Mathematik, 2014, 128 (2), pp.301-338. ⟨10.1007/s00211-014-0610-8⟩. ⟨hal-00830110⟩ Plus de détails...
We report the results of a detailed study of the spectral properties of Laplace and Stokes operators, modified with a volume penalization term designed to approximate Dirichlet conditions in the limit when a penalization parameter, $\eta$, tends to zero. The eigenvalues and eigenfunctions are determined either analytically or numerically as functions of $\eta$, both in the continuous case and after applying Fourier or finite difference discretization schemes. For fixed $\eta$, we find that only the part of the spectrum corresponding to eigenvalues $\lambda \lesssim \eta^{-1}$ approaches Dirichlet boundary conditions, while the remainder of the spectrum is made of uncontrolled, spurious wall modes. The penalization error for the controlled eigenfunctions is estimated as a function of $\eta$ and $\lambda$. Surprisingly, in the Stokes case, we show that the eigenfunctions approximately satisfy, with a precision $O(\eta)$, Navier slip boundary conditions with slip length equal to $\sqrt{\eta}$. Moreover, for a given discretization, we show that there exists a value of $\eta$, corresponding to a balance between penalization and discretization errors, below which no further gain in precision is achieved. These results shed light on the behavior of volume penalization schemes when solving the Navier-Stokes equations, outline the limitations of the method, and give indications on how to choose the penalization parameter in practical cases.
Romain Nguyen van Yen, Dmitry Kolomenskiy, Kai Schneider. Approximation of the Laplace and Stokes operators with Dirichlet boundary conditions through volume penalization: a spectral viewpoint. Numerische Mathematik, 2014, 128 (2), pp.301-338. ⟨10.1007/s00211-014-0610-8⟩. ⟨hal-00830110⟩
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, 2014, 93, pp.129-145. ⟨10.1016/j.compfluid.2014.01.003⟩. ⟨hal-01053339⟩ Plus de détails...
The present work proposes a Chebyshev-collocation Fourier-Galerkin pseudospectral method for simulating unsteady, three-dimensional, fluid flows in cylindrical geometries with pressure-driven flow through permeable boundaries. Such systems occur in diverse applications and are challenging to simulate due to an additional velocity-pressure coupling on the permeable walls through Darcy's law. The present work extends the projection method of Raspo et al. (2002) to assure Darcy's law is satisfied exactly. A multidomain solver allows the efficient treatment of open boundary conditions that necessitate permeability buffers and a sponge layer. The method is spectrally convergent, and we demonstrate that pressure-prediction is necessary to obtain second-order temporal accuracy. The ability of the method to simulate complicated physical systems is demonstrated by simulating subcritical and supercritical flows in rotating filtration in Taylor-Couette cells. For subcritical cases, numerical results show excellent agreement with analytical solutions. For supercritical cases, the numerical method accurately resolves convectively and absolutely unstable flows with traveling toroidal and helical vortical structures that are in good agreement with a local linear stability analysis and experimental observations.
Nils Tilton, Eric Serre, Denis Martinand, Richard M. Lueptow. A 3D pseudospectral algorithm for fluid flows with permeable walls. Application to filtration. Computers and Fluids, 2014, 93, pp.129-145. ⟨10.1016/j.compfluid.2014.01.003⟩. ⟨hal-01053339⟩
Bikash Sahoo, Saied Abbasbandy, Sébastien Poncet. A brief note on the computation of the Bödewadt flow with Navier slip boundary conditions. Computers and Fluids, 2014, 90, pp.133-137. ⟨10.1016/j.compfluid.2013.11.020⟩. ⟨hal-00976676⟩ Plus de détails...
In this short communication, numerical solutions are obtained for the steady Bödewadt flow of a viscous fluid subject to partial slip boundary conditions. The resulting system of nonlinear and fully coupled similarity equations are integrated accurately by a finite difference scheme and by the Keller-box method. It is observed that slip has a prominent effect on the velocity field, reducing drastically the axial velocity and the pressure. Moreover, the torque required to maintain the disk at rest decreases for increasing values of slip.
Bikash Sahoo, Saied Abbasbandy, Sébastien Poncet. A brief note on the computation of the Bödewadt flow with Navier slip boundary conditions. Computers and Fluids, 2014, 90, pp.133-137. ⟨10.1016/j.compfluid.2013.11.020⟩. ⟨hal-00976676⟩
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich H. Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89, pp.063013. ⟨hal-01087216⟩ Plus de détails...
Rayleigh-Bénard convection is investigated in rotating annular cavities at a moderate rotationrate (square root of the Taylor number) Omega= 60. The onset of convection is in the form of azimuthaltraveling waves that set in at the sidewalls and at values of the Rayleigh number significantly belowthe value of the onset of convection in an infinitely extended layer. When curvature effect becomessignificant, the waves traveling along the sidewalls have different critical Rayleigh numbers and com-plex Guinzburg-Landau equations are no longer applicable. The present study addresses the effectsof curvature and confinement on the onset of sidewall convection by using three-dimensional spectralsolutions of the Oberbeck-Boussinesq equations. Such solutions demonstrate that the curvature ofthe outer boundary promotes the onset of the wall mode, while the opposite curvature of the innerboundary tends to delay the onset of the wall mode. When radial confinement is increased the twoindependent traveling waves can interact and eventually merge to form a nearly steady pattern ofconvection.
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich H. Busse. Geometry effects on the onset of rotating Rayleigh-Bénard convection in annuli. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89, pp.063013. ⟨hal-01087216⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Marcello Meldi, Hugo Lejemble, Pierre Sagaut. On the emergence of non-classical decay regimes in multiscale/fractal generated isotropic turbulence. Journal of Fluid Mechanics, 2014, 756, pp.816-843. ⟨10.1017/jfm.2014.476⟩. ⟨hal-01064518⟩ Plus de détails...
The present paper addresses the issue of finding key parameters that may lead to the occurrence of non-classical decay regimes for fractal/multiscale generated grid turbulence. To this aim, a database of numerical simulations has been generated by the use of the eddy-damped quasi-normal Markovian (EDQNM) model. The turbulence production in the wake of the fractal/multiscale grid is modelled via a turbulence production term based on the forcing term developed for direct numerical simulations (DNS) purposes and the dynamics of self-similar wakes. The sensitivity of the numerical results to the simulation parameters has been investigated successively. The analysis is based on the observation of both the time evolution of the turbulent energy spectrum $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}E(k,t)$ and the decay of the flow statistical quantities, such as the turbulent kinetic energy $\mathcal{K}(t)$ and the energy dissipation rate $\varepsilon (t)$. A satisfactory agreement with existing experimental data published by different research teams is observed. In particular, it is observed that the key parameter that governs the nature of turbulence decay is $\alpha ={d/U_{\infty }}\, {(\varepsilon (0)/\mathcal{K}(0))}={d/L(0)} \, {(\sqrt{\mathcal{K}(0)}/U_{\infty })}$ (with $d$ the bar diameter and $U_{\infty }$ the upstream uniform velocity), which measures the ratio of the time scale largest grid bar $d/U_{\infty }$ to the turbulent time scale $\mathcal{K}(0)/\varepsilon (0)$. Two asymptotic behaviours for $\alpha \rightarrow + \infty $ and $\alpha \rightarrow 0$ are identified: (i) a fast algebraic decay law regime for rapidly decaying production terms, due to strongly modified initial kinetic energy spectrum and (ii) a real exponential decay regime associated with strong, very slowly decaying production terms. The present observations are in full agreement with conclusions drawn from recent fractal grid experiments, and it provides a physical scenario for occurrence of anomalous decay regime which encompasses previous hypotheses.
Marcello Meldi, Hugo Lejemble, Pierre Sagaut. On the emergence of non-classical decay regimes in multiscale/fractal generated isotropic turbulence. Journal of Fluid Mechanics, 2014, 756, pp.816-843. ⟨10.1017/jfm.2014.476⟩. ⟨hal-01064518⟩
Philippe Meliga, Edouard Boujo, Gregory Pujals, François Gallaire. Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder. Physics of Fluids, 2014, 26, pp.26,104101. ⟨10.1063/1.4896941⟩. ⟨hal-01082600v2⟩ Plus de détails...
We use adjoint-based gradients to analyze the sensitivity of the drag force on a square cylinder. At Re = 40, the flow settles down to a steady state. The quantity of interest in the adjoint formulation is the steady asymptotic value of drag reached after the initial transient, whose sensitivity is computed solving a steady adjoint problem from knowledge of the stable base solution. At Re = 100, the flow develops to the time-periodic, vortex-shedding state. The quantity of interest is rather the time-averaged mean drag, whose sensitivity is computed integrating backwards in time an unsteady adjoint problem from knowledge of the entire history of the vortex-shedding solution. Such theoretical frameworks allow us to identify the sensitive regions without com-puting the actually controlled states, and provide a relevant and systematic guideline on where in the flow to insert a secondary control cylinder in the attempt to reduce drag, as established from comparisons with dedicated numerical simulations of the two-cylinder system. For the unsteady case at Re = 100, we also compute an approxi-mation to the mean drag sensitivity solving a steady adjoint problem from knowledge of only the mean flow solution, and show the approach to carry valuable information in view of guiding relevant control strategy, besides reducing tremendously the re-lated numerical effort. An extension of this simplified framework to turbulent flow regime is examined revisiting the widely benchmarked flow at Reynolds number Re = 22 000, the theoretical predictions obtained in the frame of unsteady Reynolds-averaged Navier–Stokes modeling being consistent with experimental data from the literature. Application of the various sensitivity frameworks to alternative control objectives such as increasing the lift and reducing the fluctuating drag and lift is also discussed and illustrated with a few selected examples.
Philippe Meliga, Edouard Boujo, Gregory Pujals, François Gallaire. Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder. Physics of Fluids, 2014, 26, pp.26,104101. ⟨10.1063/1.4896941⟩. ⟨hal-01082600v2⟩
Alex Skillen, Alistair Revell, Alfredo Pinelli, Ugo Piomelli, Julien Favier. Flow over a Wing with Leading-Edge Undulations. AIAA Journal, 2014, 53 (2), pp.464-472. ⟨10.2514/1.J053142⟩. ⟨hal-01069899⟩ Plus de détails...
The stall-delaying properties of the humpback whale flipper have been observed and quantified in recent years, through both experimental and numerical studies. In the present work we report numerical simulations of an infinite span wing with an idealised representation of this geometry, at a Reynolds number of 1.2 × 105 . Us- ing Large Eddy Simulation, we first establish an adequate spatial resolution before also examining the spanwise extent of the domain. We then proceed to analyse these results to provide an explanation of the conditions that drive the lift observed be- yond the conventional stall angle. The undulating leading-edge geometry gives rise to a span-wise pressure gradient that drives a secondary flow towards the regions of minimum chord. In turn, this leads to the entrainment of higher-momentum fluid into the region behind the maximum chord, which energises the boundary layer and delays stall. Aside from demonstrating a significant post-stall lift, the undulations also have the added benefit of substantially reducing lift fluctuations.
Alex Skillen, Alistair Revell, Alfredo Pinelli, Ugo Piomelli, Julien Favier. Flow over a Wing with Leading-Edge Undulations. AIAA Journal, 2014, 53 (2), pp.464-472. ⟨10.2514/1.J053142⟩. ⟨hal-01069899⟩
Marco Martins Afonso, Simon Mendez, Franck Nicoud. On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid. Journal of Fluid Mechanics, 2014, 746, pp.300 -331. ⟨10.1017/jfm.2014.135⟩. ⟨hal-00957710⟩ Plus de détails...
We propose a procedure--partly analytical and partly numerical--to find the frequency and the damping rate of the small-amplitude oscillations of a massless elastic capsule immersed in a two-dimensional viscous incompressible fluid. The unsteady Stokes equations for the stream function are decomposed onto normal modes for the angular and temporal variables, leading to a fourth-order linear ordinary differential equation in the radial variable. The forcing terms are dictated by the properties of the membrane, and result into jump conditions at the interface between the internal and external media. The equation can be solved numerically, and an excellent agreement is found with a fullycomputational approach we developed in parallel. Comparisons are also shown with the results available in the scientific literature for drops, and a model based on the concept of entrained fluid is presented, which allows for a good representation of the results and a consistent interpretation of the underlying physics.
Marco Martins Afonso, Simon Mendez, Franck Nicoud. On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid. Journal of Fluid Mechanics, 2014, 746, pp.300 -331. ⟨10.1017/jfm.2014.135⟩. ⟨hal-00957710⟩
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, 2014, 54 (4-6), pp.378-382. ⟨10.1002/ctpp.201410026⟩. ⟨hal-01053281⟩ Plus de détails...
To support ITER divertor design, the WEST project on Tore Supra aims at studying high heat fluxes on tungsten monoblock during long pulses. In that persective, a particular attention is paid to simulate the edge plasma interaction with complex PFCs using the transport code SOLEDGE2D-EIRENE. The plasma response to a heating and puffing scenario is described as well as the so-called divertor density regimes, characterizing the operational domain of the WEST divertor. These results are compared for two different magnetic configurations: a semi-open double null divertor with the X-point away from the target plates and a shallow divertor configuration with the X-point close to the targets.
Hugo Bufferand, Jérome Bucalossi, Guido Ciraolo, Nicolas Fedorczak, Philippe Ghendrih, et al.. Density regimes and heat flux deposition in the WEST shallow divertor configuration. Contributions to Plasma Physics, 2014, 54 (4-6), pp.378-382. ⟨10.1002/ctpp.201410026⟩. ⟨hal-01053281⟩
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, 2014, 56 (122001), ⟨10.1088/0741-3335/56/12/122001⟩. ⟨hal-01225185⟩ Plus de détails...
We present a comprehensive picture of the mechanisms driving the transition from subsonic to supersonic flows in tokamak plasmas. We demonstrate that supersonic parallel flows into the divertor volume are ubiquitous at low density and governed by the divertor magnetic geometry. As the density is increased, subsonic divertor plasmas are recovered. On detachment, we show the change in particle source can also drive the transition to a supersonic regime. The comprehensive theoretical analysis is completed by simulations in ITER geometry. Such results are essential in assessing the divertor performance and when interpreting measurements and experimental evidence. The generation of large-scale flows in laboratory plasma is a highly non-linear problem. In a standard fashion it is considered that the flows remain subsonic away from the wall, the occurrence of supersonic flows being singular. We show here that the geometrical features of key configurations for fusion plasma can lead to supersonic flows.
Hugo Bufferand, Guido Ciraolo, Guilhem Dif-Pradalier, Philippe Ghendrih, Patrick Tamain, et al.. Magnetic geometry and particle source drive of supersonic divertor regimes. Plasma Physics and Controlled Fusion, 2014, 56 (122001), ⟨10.1088/0741-3335/56/12/122001⟩. ⟨hal-01225185⟩
Julien Favier, Alistair Revell, Alfredo Pinelli. A Lattice Boltzmann - Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects. Journal of Computational Physics, 2014, 261, pp.145-161. ⟨10.1016/j.jcp.2013.12.052⟩. ⟨hal-00822044⟩ Plus de détails...
A numerical approach based on the Lattice Boltzmann and Immersed Boundary methods is pro- posed to tackle the problem of the interaction of moving and/or deformable slender solids with an incompressible fluid flow. The method makes use of a Cartesian uniform lattice that encom- passes both the fluid and the solid domains. The deforming/moving elements are tracked through a series of Lagrangian markers that are embedded in the computational domain. Differently from classical projection methods applied to advance in time the incompressible Navier-Stokes equa- tions, the baseline Lattice Boltzmann fluid solver is free from pressure corrector step, which is known to affect the accuracy of the boundary conditions. Also, in contrast to other immersed boundary methods proposed in the literature, the proposed algorithm does not require the in- troduction of any empirical parameter. In the case of rigid bodies, the position of the markers delimiting the surface of an object is updated by tracking both the position of the center of mass of the object and its rotation using Newton's Laws and the conservation of angular momentum. The dynamics of a flexible slender structure is determined as a function of the forces exerted by the fluid, its flexural rigidity and the tension necessary to enforce the filament inextensibility. For both rigid and deformable bodies, the instantaneous no-slip and impermeability conditions on the solid boundary are imposed via external and localized body forces which are consistently introduced into the Lattice Boltzmann equation. The validation test-cases for rigid bodies in- clude the case of an impulsively started plate and the sedimentation of particles under gravity in a fluid initially at rest. For the case of deformable slender structures we consider the beating of both a single filament and a pair filaments induced by the interaction with an incoming uniformly streaming flow.
Julien Favier, Alistair Revell, Alfredo Pinelli. A Lattice Boltzmann - Immersed Boundary method to simulate the fluid interaction with moving and slender flexible objects. Journal of Computational Physics, 2014, 261, pp.145-161. ⟨10.1016/j.jcp.2013.12.052⟩. ⟨hal-00822044⟩
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, 2014, 54 (4-6), pp.373-377. ⟨10.1002/ctpp.201410028⟩. ⟨hal-01050666⟩ Plus de détails...
The penalization method is used to model the interaction of 3D probe with an isothermal plasma. Density maps show that the region perturbed by the obstacle, is not restricted to its near neighbourhood, but can extend to the whole SOL. In the particular case of a probe, which is used to measure local plasma parameters, this impact can lead to violation of assumptions of locality of the perturbation usually used in determining Mach number from the imbalance in density on both sides of the probe.
Alejandro Paredes, Eric Serre, Frédéric Schwander, Philippe Ghendrih, Patrick Tamain. Numerical fluid modelling of the plasma edge response to a 3D object and application to mach probe measurements. Contributions to Plasma Physics, 2014, 54 (4-6), pp.373-377. ⟨10.1002/ctpp.201410028⟩. ⟨hal-01050666⟩
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, 2014, 54 (4-6), pp.543-548. ⟨10.1002/ctpp.201410087⟩. ⟨hal-01019696⟩ Plus de détails...
An issue for Langmuir probe measurements of SOL turbulence concerns the impact of the probe itself on plasma transport. The aim of this paper is to investigate this issue with a synthetic reconstruction of Langmuir probe measurements by inserting a synthetic probe into a 2D fluid SOL turbulence code. The effect of a biased probe is analysed as a function of its size. It is shown that the probe creates a transport barrier whose effect is non-local and affects the current's circulation in the plasma. The plasma density is depleted by the presence of the probe as well as the electrostatic potential. A strong impact on turbulence can also be observed. Such observations imply that the probed turbulence can differ significantly from the probe-free turbulence
Clothilde Colin, Patrick Tamain, Philippe Ghendrih, Frederic Schwander, Eric Serre. Impact of a Langmuir probe on turbulence measurements in the Scrape-Off-Layer of tokamaks. Contributions to Plasma Physics, 2014, 54 (4-6), pp.543-548. ⟨10.1002/ctpp.201410087⟩. ⟨hal-01019696⟩
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, 2014, 54 (4-6), pp.555-559. ⟨10.1002/ctpp.201410017⟩. ⟨hal-01053290⟩ Plus de détails...
The 3D fluid turbulence code TOKAM3X is used to investigate the 3D properties of edge turbulent transport and their impact on poloidal asymmetries. Simulations are run in circular limited plasmas in a domain covering both closed and open flux surfaces. Turbulence characteristics exhibit large inhomogeneities both in the radial and poloidal directions reminiscent of experimental observations. The low field side mid-plane in particular is found to be locally more fluctuating and intermittent than the rest of the Scrape-Off-Layer (SOL). As a consequence of this asymmetry, radial turbulent transport, that represents 80 to 90% of the total radial flux, is strongly ballooned, with 75% of the flux flowing through LFS. The equilibrium of the edge plasma is impacted by this asymmetry through the existence of large amplitude asymmetric parallel flows as well as through the development of poloidally asymmetric radial decay lengths making it impossible to define a single SOL width.
Patrick Tamain, Hugo Bufferand, Guido Ciraolo, Clothilde Colin, Philippe Ghendrih, et al.. 3D properties of edge turbulent transport in full-torus simulations and their impact on poloidal asymmetries. Contributions to Plasma Physics, 2014, 54 (4-6), pp.555-559. ⟨10.1002/ctpp.201410017⟩. ⟨hal-01053290⟩
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, 2014, 274, pp.283-298. ⟨hal-01087225⟩ Plus de détails...
To properly address turbulent transport in the edge plasma region of a tokamak, it is mandatory to describe the particle and heat outflow on wall components, using an accurate representation of the wall geometry. This is challenging for many plasma transport codes, which use a structured mesh with one coordinate aligned with magnetic surfaces. We propose here a penalization technique that allows modelingof particle and heat transport using such structured mesh, while also accounting for geometrically complex plasma-facing components. Solid obstacles are considered as particle and momentum sinks whereas ionic and electronic temperature gradients are imposed on both sides of the obstacles along the magnetic field direction using delta functions (Dirac). Solutions exhibit plasma velocities (M=1) and temperatures fluxes at the plasma–wall boundaries that match with boundary conditions usually implemented in fluid codes. Grid convergence and error estimates are found to be in agreement with theoretical results obtained for neutral fluid conservation equations. The capability of the penalization technique is illustrated by introducing the non-collisional plasma region expected by the kinetic theory in the immediate vicinity of the interface, that is impossible when considering fluid boundary conditions. Axisymmetric numerical simulations show the efficiency of the method to investigate the large-scale transport at the plasma edge including the separatrix and in realistic complex geometries while keeping a simple structured grid.
Alejandro Paredes, Hugo Bufferand, Guido Ciraolo, Frédéric Schwander, Eric Serre, et al.. A penalization technique to model plasma facing components in a tokamak with temperature variations. Journal of Computational Physics, 2014, 274, pp.283-298. ⟨hal-01087225⟩
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, ⟨10.1007/978-3-319-01601-6_21⟩. ⟨hal-01098589⟩ Plus de détails...
In this work, we improve an existing pseudospectral algorithm, in order to extend its properties to a multidomain patching of a rotating cavity. Viscous rotating flows have been widely studied over the last decades, either on industrial or aca-demic approaches. Nevertheless, the range of Reynolds numbers reached in indus-trial devices implies very high resolutions of the spatial problem, which are clearly unreachable using a monodomain approach. Hence, we worked on the multido-main extension of the existing divergence-free Navier-Stokes solver with a Schur approach. The particularity of such an approach is that it does not require any sub-domain superposition: the value of a variable on the boundary between two adjacent subdomains is treated as a boundary condition of a local Helmholtz solver. This value is computed on a direct way via a so-called continuity influence matrix and the derivative jump of an homogeneous solution computed independently on each subdomain. Such a method is known to have both good scalability and accuracy. It has been validated on two well documented three-dimensional rotating flows.
Guillaume Fontaine, Sébastien Poncet, Eric Serre. Multidomain Extension of a Pseudospectral Algorithm for the Direct Simulation of Wall-Confined Rotating Flows. M. Azaiez, H. El Fekih, J.S. Hesthaven. Lecture Notes in Computational Science and Engineering, 95, Springer, pp.261 - 271, 2014, ⟨10.1007/978-3-319-01601-6_21⟩. ⟨hal-01098589⟩
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, 2014, 54 (4-6), pp.432-436. ⟨10.1002/ctpp.201410018⟩. ⟨hal-01050505⟩ Plus de détails...
We present numerical simulations of plasma transport obtained with the SOLEDGE2D code coupled to the EIRENE Montecarlo code for neutrals. We consider a double null magnetic configuration in a WEST geometry. Density and temperatures parallel profiles in the SOL domain are presented as well as Mach profile. We detail how using the penalization technique we are able to model plasma transport up to the first wall having access to energy and particle fluxes on the entire chamber wall. Moreover, we present the computed 2D contour map of the plasma mach number and of the magnitude of the ionisation source term in the whole poloidal section, emphasizing how complex and realistic geometries can be handled thanks to the penalization technique.
Guido Ciraolo, Hugo Bufferand, Philippe Ghendrih, Patrick Tamain, Jérome Bucalossi, et al.. Investigation of edge and SOL particle flux patterns in high density regimes using SOLEDGE2D-EIRENE code. Contributions to Plasma Physics, 2014, 54 (4-6), pp.432-436. ⟨10.1002/ctpp.201410018⟩. ⟨hal-01050505⟩
Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge. Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89 (3), pp.033013. ⟨10.1103/physreve.89.033013⟩. ⟨hal-01087726⟩ Plus de détails...
Small-scale anisotropic intermittency is examined in three-dimensional incompressible magnetohydrodynamic turbulence subjected to a uniformly imposed magnetic field. Orthonormal wavelet analyses are applied to direct numerical simulation data at moderate Reynolds number and for different interaction parameters. The magnetic Reynolds number is sufficiently low such that the quasistatic approximation can be applied. Scale-dependent statistical measures are introduced to quantify anisotropy in terms of the flow components, either parallel or perpendicular to the imposed magnetic field, and in terms of the different directions. Moreover, the flow intermittency is shown to increase with increasing values of the interaction parameter, which is reflected in strongly growing flatness values when the scale decreases. The scale-dependent anisotropy of energy is found to be independent of scale for all considered values of the interaction parameter. The strength of the imposed magnetic field does amplify the anisotropy of the flow.
Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge. Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2014, 89 (3), pp.033013. ⟨10.1103/physreve.89.033013⟩. ⟨hal-01087726⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Sébastien Poncet, Thien Duy Nguyen, Souad Harmand, Julien Pellé, Riccardo da Soghe, et al.. Turbulent impinging jet flow into an unshrouded rotor-stator system: Hydrodynamics and heat transfer. International Journal of Heat and Fluid Flow, 2013, 44, pp.719-734. ⟨10.1016/j.ijheatfluidflow.2013.10.001⟩. ⟨hal-00976669⟩ Plus de détails...
New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k-w SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor-stator system. The cavity is characterized by a dimensionless spacing interval G=0.02 and a low aspect ratio for the jet e/D=0.25. Jet Reynolds numbers ranging from 17200 to 43000 and rotational Reynolds numbers between 33000 and 532000 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotation-dominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k-wSST model overestimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.
Sébastien Poncet, Thien Duy Nguyen, Souad Harmand, Julien Pellé, Riccardo da Soghe, et al.. Turbulent impinging jet flow into an unshrouded rotor-stator system: Hydrodynamics and heat transfer. International Journal of Heat and Fluid Flow, 2013, 44, pp.719-734. ⟨10.1016/j.ijheatfluidflow.2013.10.001⟩. ⟨hal-00976669⟩
Journal: International Journal of Heat and Fluid Flow
Marie Farge, H. Keith Moffatt, Kai Schneider. FOREWORD: Turbulence Colloquium Marseille 2011. Journal of Turbulence, 2013, 14 (9), pp.39-42. ⟨10.1080/14685248.2013.851836⟩. ⟨hal-01300038⟩ Plus de détails...
Marie Farge, H. Keith Moffatt, Kai Schneider. FOREWORD: Turbulence Colloquium Marseille 2011. Journal of Turbulence, 2013, 14 (9), pp.39-42. ⟨10.1080/14685248.2013.851836⟩. ⟨hal-01300038⟩
Elena Floriani, Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Ricardo Lima. Self-regulation of turbulence bursts and transport barriers. Plasma Physics and Controlled Fusion, 2013, 55 (9), pp.095012. ⟨10.1088/0741-3335/55/9/095012⟩. ⟨hal-00733279⟩ Plus de détails...
The interplay between turbulent bursts and transport barriers is analyzed with a simplified model of interchange turbulence in the Scrape-Off Layer of magnetically confined plasmas. The turbulent bursts spread into the transport barriers, and, depending on the competing magnitude of the burst and stopping capability of the barrier can burn through. Two models of transport barriers are presented, a hard barrier where all turbulent modes are stable in a prescribed region and a soft barrier with external plasma biasing. This process can be modeled on the basis of competing stochastic processes. For classes of probability density function of these processes one can predict the heavy tail properties of the bursts downstream from the barrier, either exponential for a leaky barrier, or with power laws, for a tight barrier. The intrinsic probing of the transport barriers by the turbulent bursts thus gives access to properties of the transport barriers. The main stochastic variables of the two models addressed here are the barrier width and the spreading distance of the turbulent bursts within the barrier together with their level of correlation. One finds that in the case of a barrier located in the Scrape-Off-Layer, the stochastic model predicts a leaky barrier with an exponential probability density function of escaping turbulent bursts in agreement with the simulation data.
Elena Floriani, Guido Ciraolo, Philippe Ghendrih, Yanick Sarazin, Ricardo Lima. Self-regulation of turbulence bursts and transport barriers. Plasma Physics and Controlled Fusion, 2013, 55 (9), pp.095012. ⟨10.1088/0741-3335/55/9/095012⟩. ⟨hal-00733279⟩
Bikash Sahoo, Sébastien Poncet. Blasius flow and heat transfer of fourth-grade fluid with slip. Applied Mathematics and Mechanics, 2013, 34 (12), pp.1465-1480. ⟨10.1007/s10483-013-1760-6⟩. ⟨hal-00975631⟩ Plus de détails...
This investigation deals with the effects of slip, magnetic field, and non-Newtonian flow parameters on the flow and heat transfer of an incompressible, electrically conducting fourth-grade fluid past an infinite porous plate. The heat transfer analysis is carried out for two heating processes. The system of highly non-linear differential equations is solved by the shooting method with the fourth-order Runge-Kutta method for moderate values of the parameters. The effective Broyden technique is adopted in order to improve the initial guesses and to satisfy the boundary conditions at infinity. An exceptional cross-over is obtained in the velocity profile in the presence of slip. The fourth-grade fluid parameter is found to increase the momentum boundary layer thickness, whereas the slip parameter substantially decreases it. Similarly, the non-Newtonian fluid parameters and the slip have opposite effects on the thermal boundary layer thickness.
Bikash Sahoo, Sébastien Poncet. Blasius flow and heat transfer of fourth-grade fluid with slip. Applied Mathematics and Mechanics, 2013, 34 (12), pp.1465-1480. ⟨10.1007/s10483-013-1760-6⟩. ⟨hal-00975631⟩
Giorgio Giorgiani, David Modesto, Sonia Fernández-Méndez, Antonio Huerta. High-order continuous and discontinuous Galerkin methods for wave problems. International Journal for Numerical Methods in Fluids, 2013, 73(10), pp.883-903. ⟨10.1002/fld.3828⟩. ⟨hal-01717513⟩ Plus de détails...
Three Galerkin methods —continuous Galerkin (CG), Compact Discontinuous Galerkin (CDG) and Hybridizable Discontinuous Galerkin (HDG)— are compared in terms of performance and computational efficiency in two-dimensional scattering problems for low and high-order approximations. The total number of degrees of freedom and the total runtime are used for this correlation as well as the corresponding precision. The comparison is carried out through various numerical examples. The superior performance of high-order elements is shown. At the same time, similar capabilities are shown for CG and HDG, when high-order elements are adopted, both of them clearly outperforming CDG.
Giorgio Giorgiani, David Modesto, Sonia Fernández-Méndez, Antonio Huerta. High-order continuous and discontinuous Galerkin methods for wave problems. International Journal for Numerical Methods in Fluids, 2013, 73(10), pp.883-903. ⟨10.1002/fld.3828⟩. ⟨hal-01717513⟩
Journal: International Journal for Numerical Methods in Fluids
Sébastien Poncet, Stéphane Viazzo, Adrien Aubert, Riccardo da Soghe, Cosimo Bianchini. Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark. International Journal of Heat and Fluid Flow, 2013, 44, pp.229-238. ⟨10.1016/j.ijheatfluidflow.2013.05.018⟩. ⟨hal-00975636⟩ Plus de détails...
The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette-Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Rea, the exponent a = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k-w SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement.
Sébastien Poncet, Stéphane Viazzo, Adrien Aubert, Riccardo da Soghe, Cosimo Bianchini. Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark. International Journal of Heat and Fluid Flow, 2013, 44, pp.229-238. ⟨10.1016/j.ijheatfluidflow.2013.05.018⟩. ⟨hal-00975636⟩
Journal: International Journal of Heat and Fluid Flow
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, 2013, 438, pp.S368-S371. ⟨10.1016/j.jnucmat.2013.01.070⟩. ⟨hal-00920748⟩ Plus de détails...
The ballooned nature of cross-field transport is shown to govern the steady state divertor imbalance of the energy flux leading to a factor 10 between the low field side and high field energy flux. An even stronger ratio is found for the divertor temperatures. Conversely the particle flux is expected to be a factor 10 larger on the high field side than on the low field side. The transition to detachment, close to divertor thermal collapse, exhibits several constraints to maintain steady state solutions. These constraints, related in particular to a large drop of the divertor density upon detachment, are shown to strongly correlate the pressure and particle flux variation along the field line and consequently the various loss channels. This delicate balance between different mechanisms is a possible understanding of the difficulty reported in detached plasma operation and simulation.
Philippe Ghendrih, Thomas Auphan, B. Bensiali, Marco Bilanceri, K. Bodi, et al.. Divertor imbalance and divertor density regimes for ballooned cross-field turbulence. Journal of Nuclear Materials, 2013, 438, pp.S368-S371. ⟨10.1016/j.jnucmat.2013.01.070⟩. ⟨hal-00920748⟩
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Two-dimensional simulation of the fluttering instability using a pseudospectral method with volume penalization. Computers & Structures, 2013, 122, pp. 101-112 ⟨10.1016/j.compstruc.2012.12.007⟩. ⟨hal-01299992⟩ Plus de détails...
We present a new numerical scheme for the simulation of deformable objects immersed in a viscous incompressible fluid. The two-dimensional Navier-Stokes equations are discretized with an efficient Fourier pseudo-spectral scheme. Using the volume penalization method arbitrary inflow conditions can be enforced, together with the no-slip conditions at the boundary of the immersed flexible object. With respect to Kolomenskiy and Schneider (2009) [1], where rigid moving obstacles have been considered, the present work extends the volume penalization method to account for moving deformable objects while avoiding numerical oscillations in the hydrodynamic forces. For the solid part, a simple and accurate one-dimensional model, the non-linear beam equation, is employed. The coupling between the fluid and solid parts is realized with a fast explicit staggered scheme. The method is applied to the fluttering instability of a slender structure immersed in a free stream. This coupled non-linear system can enter three distinct states: stability of the initial condition or maintenance of an either periodic or chaotic fluttering motion. We present a detailed parameter study for different Reynolds numbers and reduced free-stream velocities. The dynamics of the transition from a periodic to a chaotic state is investigated. The results are compared with those obtained by an inviscid vortex shedding method [2] and by a viscous linear stability analysis [3], yielding for both satisfactory agreement. New results concerning the transition to chaos are presented.
Thomas Engels, Dmitry Kolomenskiy, Kai Schneider, Jörn Sesterhenn. Two-dimensional simulation of the fluttering instability using a pseudospectral method with volume penalization. Computers & Structures, 2013, 122, pp. 101-112 ⟨10.1016/j.compstruc.2012.12.007⟩. ⟨hal-01299992⟩
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Stefano Lepri, Roberto Livi. Particle model for nonlocal heat transport in fusion plasmas. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2013, 87 (2), ⟨10.1103/PhysRevE.87.023102⟩. ⟨hal-01464720⟩ Plus de détails...
We present a simple stochastic, one-dimensional model for heat transfer in weakly collisional media as fusion plasmas. Energies of plasma particles are treated as lattice random variables interacting with a rate inversely proportional to their energy schematizing a screened Coulomb interaction. We consider both the equilibrium (microcanonical) and nonequilibrium case in which the system is in contact with heat baths at different temperatures. The model exhibits a characteristic length of thermalization that can be associated with an interaction mean free path and one observes a transition from ballistic to diffusive regime depending on the average energy of the system. A mean-field expression for heat flux is deduced from system heat transport properties. Finally, it is shown that the nonequilibrium steady state is characterized by long-range correlations. DOI: 10.1103/PhysRevE.87.023102
Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Stefano Lepri, Roberto Livi. Particle model for nonlocal heat transport in fusion plasmas. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2013, 87 (2), ⟨10.1103/PhysRevE.87.023102⟩. ⟨hal-01464720⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Souad Harmand, Julien Pellé, Sébastien Poncet, Igor Shevchuk. Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet. International Journal of Thermal Sciences, 2013, 67, pp.1-30. ⟨10.1016/j.ijthermalsci.2012.11.009⟩. ⟨hal-00975626⟩ Plus de détails...
Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental / theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steadystate (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice.
Souad Harmand, Julien Pellé, Sébastien Poncet, Igor Shevchuk. Review of fluid flow and convective heat transfer within rotating disk cavities with impinging jet. International Journal of Thermal Sciences, 2013, 67, pp.1-30. ⟨10.1016/j.ijthermalsci.2012.11.009⟩. ⟨hal-00975626⟩
Journal: International Journal of Thermal Sciences
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, 2013, 438, pp.625-628. ⟨10.1016/j.jnucmat.2013.01.131⟩. ⟨hal-01101342⟩ Plus de détails...
The original and computationally efficient volume penalization technique Ref. [1], proposed for an isothermal plasma to recover the Bohm boundary condition at the plasma–obstacle interface, is extended to model 3D obstacles. It is then generalized to handle electron and ion temperatures in a 1D model. Results in 3D simulations show that the geometry of secondary limiter has an influence on the density and particle flux profiles, breaking its toroidal symmetry and introducing profile gaps of magnitude of 20%. On the other hand, the generalization of the penalization scheme to the non-isothermal case demands to deal with new Neumann conditions on the heat fluxes. Those boundary conditions require the introduction of new mask functions to ensure that the Bohm boundary condition remains satisfied.
A. Paredes, Hugo Bufferand, F. Schwander, G. Ciraolo, E. Serre, et al.. Penalization technique to model wall-component impact on heat and mass transport in the tokamak edge. Journal of Nuclear Materials, 2013, 438, pp.625-628. ⟨10.1016/j.jnucmat.2013.01.131⟩. ⟨hal-01101342⟩
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, 2013, 438, pp.445-448. ⟨10.1016/j.jnucmat.2013.01.090⟩. ⟨hal-01101345⟩ Plus de détails...
In order to model plasma interaction with full complexity of the geometry of PFCs, an immersed method to impose boundary conditions has been implemented in the transport code SolEdge2D. This penalization technique has proven to properly recover Bohm boundary conditions, including supersonic solutions at the sheath entrance. The role of the ionization source has been taken into account by coupling SolEdge2D with the 3D kinetic neutral code Eirene. Density regimes are properly recovered and major differences between core located and divertor located ionization source regimes are emphasized. One also presents main chamber wall recycling regime simulations that can now be addressed with simulations of the entire edge plasma up to the wall.
Hugo Bufferand, B. Bensiali, J. Bucalossi, G. Ciraolo, P. Genesio, et al.. Near wall plasma simulation using penalization technique with the transport code Soledge2D-EIRENE. Journal of Nuclear Materials, 2013, 438, pp.445-448. ⟨10.1016/j.jnucmat.2013.01.090⟩. ⟨hal-01101345⟩
P. Sagaut, S. Deck, M. Terracol. Multiscale and multiresolution approaches in turbulence (second edition). Imperial College Press, 2, 2013. ⟨hal-01313533⟩ Plus de détails...
P. Sagaut, S. Deck, M. Terracol. Multiscale and multiresolution approaches in turbulence (second edition). Imperial College Press, 2, 2013. ⟨hal-01313533⟩
Eric Serre, Mathieu Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a french-german collaborative evaluation of LES and DES. Computers and Fluids, 2013, 78, pp.10-23. ⟨ujm-00860576⟩ Plus de détails...
The paper presents a comparative analysis of recent simulations, conducted in the framework of a French-German collaboration on LES of Complex Flows, for the so-called Ahmed body at Reynolds number 768000 and slant angle 25°. It provides a juxtaposition of results obtained with different eddy-resolving modeling approaches, i.e. two Large Eddy Simulations (LES) on body-fitted curvilinear grids, a stabilized spectral method and a Detachted Eddy Simulation (DES) on an unstructured grid. The paper presents a comprehensive data base including both instantaneous and statistical data. A central achievement is the comparative assessment of the different approaches with an appreciation of the respective advantages and disadvantages of the various methods. In particular, issues on computational cost and ease of implementation are addressed in addition to the quality of results.
Eric Serre, Mathieu Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a french-german collaborative evaluation of LES and DES. Computers and Fluids, 2013, 78, pp.10-23. ⟨ujm-00860576⟩
Imran Afgan, Sofiane Benhamadouche, Xingsi Han, Pierre Sagaut, Dominique Laurence. Flow over a flat plate with uniform inlet and incident coherent gusts. Journal of Fluid Mechanics, 2013, 720, pp.457-485. ⟨10.1017/jfm.2013.25⟩. ⟨hal-01715550⟩ Plus de détails...
The flow over a flat plate at a Reynolds number of 750 is numerically investigated via fine Large Eddy Simulation (LES) first, at normal (90 0) and then at oblique (45 0) incidence flow direction with a uniform steady inlet. The results are in complete agreement to the Direct Numerical Simulation (DNS) and experimental data, thereby serving as a validation for the present simulations. For the normal (90 0) uniform inflow case, coherent vortices are alternatively shed from both leading edges of the plate, whereas for the oblique (45 0) uniform inflow case the shedding from the two sides of the plate interact strongly resulting in a quasi-periodic force response. The normal flat plate is then analyzed with an incident gust signal with varying amplitude and time period. For these incident coherent gust cases, a reference test case with variable coherent inlet is first studied and the results are compared to a steady inlet simulation, with a detailed analysis of the flow behavior and the wake response under the incident gust. Finally, the flat plate response to 16 different gust profiles is studied. Transient drag reconstruction for these incident coherent gust cases is then presented based on frequency dependent transfer function and phase spectrum analysis.
Imran Afgan, Sofiane Benhamadouche, Xingsi Han, Pierre Sagaut, Dominique Laurence. Flow over a flat plate with uniform inlet and incident coherent gusts. Journal of Fluid Mechanics, 2013, 720, pp.457-485. ⟨10.1017/jfm.2013.25⟩. ⟨hal-01715550⟩
Rodrigo M. Pereira, Romain Nguyen-Van-Yen, Marie Farge, Kai Schneider. Wavelet methods to eliminate resonances in the Galerkin-truncated Burgers and Euler equations. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2013, 87 (3), pp.033017. ⟨10.1103/PhysRevE.87.033017⟩. ⟨hal-00830421⟩ Plus de détails...
It is well known that solutions to the Fourier-Galerkin truncation of the inviscid Burgers equation (and other hyperbolic conservation laws) do not converge to the physically relevant entropy solution after the formation of the first shock. This loss of convergence was recently studied in detail in [S. S. Ray et al., Phys. Rev. E 84, 016301 (2011)], and traced back to the appearance of a spatially localized resonance phenomenon perturbing the solution. In this work, we propose a way to remove this resonance by filtering a wavelet representation of the Galerkin-truncated equations. A method previously developed with a complex-valued wavelet frame is applied and expanded to embrace the use of real-valued orthogonal wavelet basis, which we show to yield satisfactory results only under the condition of adding a safety zone in wavelet space. We also apply the complex-valued wavelet based method to the 2D Euler equation problem, showing that it is able to filter the resonances in this case as well.
Rodrigo M. Pereira, Romain Nguyen-Van-Yen, Marie Farge, Kai Schneider. Wavelet methods to eliminate resonances in the Galerkin-truncated Burgers and Euler equations. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2013, 87 (3), pp.033017. ⟨10.1103/PhysRevE.87.033017⟩. ⟨hal-00830421⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Eric Eric Serre, M. Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a French-German collaborative evaluation of LES and DES. Computers and Fluids, 2013, 78, pp.10-23. ⟨10.1016/j.compfluid.2011.05.017⟩. ⟨hal-01101350⟩ Plus de détails...
The paper presents a comparative analysis of recent simulations, conducted in the framework of a French-German collaboration on LES of Complex Flows, for the so-called Ahmed body at Reynolds number 768000 and slant angle 25°. It provides a juxtaposition of results obtained with different eddy-resolving modeling approaches, i.e. two Large Eddy Simulations (LES) on body-fitted curvilinear grids, a stabilized spectral method and a Detachted Eddy Simulation (DES) on an unstructured grid. The paper presents a comprehensive data base including both instantaneous and statistical data. A central achievement is the comparative assessment of the different approaches with an appreciation of the respective advantages and disadvantages of the various methods. In particular, issues on computational cost and ease of implementation are addressed in addition to the quality of results.
Eric Eric Serre, M. Minguez, R. Pasquetti, Emmanuel Guilmineau, G.B. Deng, et al.. On simulating the turbulent flow around the Ahmed body: a French-German collaborative evaluation of LES and DES. Computers and Fluids, 2013, 78, pp.10-23. ⟨10.1016/j.compfluid.2011.05.017⟩. ⟨hal-01101350⟩
Elena Alekseenko, Bernard Roux, Anton Sukhinov, Richard Kotarba, Dominique Fougere. Nonlinear hydrodynamics in a Mediterranean lagoon. Nonlinear Processes in Geophysics, 2013, 20 (2), pp.189-198. ⟨10.5194/npg-20-189-2013⟩. ⟨hal-01464721⟩ Plus de détails...
The paper addresses the application of the nonlinear hydrodynamics model (RANS (Reynolds-averaged Navier-Stokes) equations) in a wide semi-enclosed Mediterranean lagoon (Berre lagoon), considering three ă natural forcing functions, i.e., sea tide propagating through a long narrow channel, wind and runoff. Main attention is focused to characteristic velocities (at free surface and bottom) and to free surface elevation associated to each of these three mechanisms, with special attention to the nearshore areas (i.e., in shallow water). The most interesting result concerns wind effects which, due to Berre lagoon bathymetry, give rise to downwind coastal jets, alongshore, in shallow water areas. Such coastal jets were never mentioned before in Berre lagoon literature.
Elena Alekseenko, Bernard Roux, Anton Sukhinov, Richard Kotarba, Dominique Fougere. Nonlinear hydrodynamics in a Mediterranean lagoon. Nonlinear Processes in Geophysics, 2013, 20 (2), pp.189-198. ⟨10.5194/npg-20-189-2013⟩. ⟨hal-01464721⟩
Tatyana Lyubimova, Bernard Roux, Shunlong Luo, Ya. N Parshakova, Natalya Shumilova. Modeling of the near-field distribution of pollutants coming from a ă coastal outfall. Nonlinear Processes in Geophysics, 2013, 20 (2), pp.257-266. ⟨10.5194/npg-20-257-2013⟩. ⟨hal-01464728⟩ Plus de détails...
The present study concerns the 3-D distribution of pollutants emitted ă from a coastal outfall in the presence of strong sea currents. The ă problem is solved using the nonlinear Reynolds-averaged Navier-Stokes ă equations in the framework of the k-epsilon model. The constants of the ă logarithmic law for the vertical velocity profile in the bottom boundary ă layer are obtained by processing experimental data from acoustic Doppler ă current profilers (ADCPs). The near-field distribution of pollutants at ă different distances from the diffuser is obtained in terms of the ă ambient flow velocity (steady or with tidal effect) and outfall ă discharge characteristics. It is shown that even in the case where the ă effluent density is substantially lower than the ambient sea water ă density the plume can impact the seabed, creating a risk of pollution of ă removable bottom sediments.
Tatyana Lyubimova, Bernard Roux, Shunlong Luo, Ya. N Parshakova, Natalya Shumilova. Modeling of the near-field distribution of pollutants coming from a ă coastal outfall. Nonlinear Processes in Geophysics, 2013, 20 (2), pp.257-266. ⟨10.5194/npg-20-257-2013⟩. ⟨hal-01464728⟩
Dmitry Kolomenskiy, Thomas Engels, Kai Schneider. Numerical Modelling of Flexible Heaving Foils. Journal of Aero Aqua Bio-mechanisms, 2013, 3 (1), pp. 22-28 ⟨10.5226/jabmech.3.22⟩. ⟨hal-01299235⟩ Plus de détails...
We consider the effects of chordwise flexibility on the aerodynamic performance of flapping wings using numerical simulation. The two-dimensional Navier-Stokes equations are solved using a Fourier pseudo-spectral method with no-slip boundary conditions imposed by the volume penalization method. The flexible wing is modelled with a non-linear beam equation. Our numerical simulations of heaving plates show that the maximum thrust is achieved at a stroke frequency lower than resonant, which is in agreement with experiments. The oscillatory part of the force only increases in amplitude when the frequency increases. We also consider aerodynamic interactions between two heaving foils.
Dmitry Kolomenskiy, Thomas Engels, Kai Schneider. Numerical Modelling of Flexible Heaving Foils. Journal of Aero Aqua Bio-mechanisms, 2013, 3 (1), pp. 22-28 ⟨10.5226/jabmech.3.22⟩. ⟨hal-01299235⟩
Pierre Magnico. Influence of the ion-solvent interactions on ionic transport through ion-exchange-membranes. Journal of Membrane Science, 2013, 442, pp.272-285. ⟨10.1016/j.memsci.2013.04.003⟩. ⟨hal-00968171⟩ Plus de détails...
Ionic transport through ionic exchange membrane cannot be interpreted by the Nernst-Planck equation if the ion density is high, particularly in the membrane. In order to extend the density range, excess terms must be added to the chemical potential. These terms are computed by considering charged hard spheres embedded in a dielectric continuum. In this aim and owing to heterogeneity of the electrolytic solution the density function theory (DFT) is used. A previous work has been carried out with a homogeneous and amorphous solvent. Here an extension including the finite size of the solvent molecule and the local dielectric properties via the dielectric coefficient is presented. The electro-osmosis is also examined. The selectivity at equilibrium, the density profiles and the voltammograms are analysed. The numerical results obtained with NaCl and CaCl2 show that the physical properties of the solvent decrease the selectivity and increases the conductivity of the membrane systems. In the same time, the dielectric properties increase the electro-osmotic effects on the ionic transport. The approach described in this work can be used to study the solvent confinement effect inside the membrane on the ionic transport.
Pierre Magnico. Influence of the ion-solvent interactions on ionic transport through ion-exchange-membranes. Journal of Membrane Science, 2013, 442, pp.272-285. ⟨10.1016/j.memsci.2013.04.003⟩. ⟨hal-00968171⟩
M. Farge, K. Schneider, Olivier Pannekoucke, R. Nguyen Van Yen. Multiscale representations: fractals, self-similar random processes and wavelets. H.J. Fernando. Handbook of Environmental Fluid Dynamics, II, Taylor and Francis, pp.311-332, 2013. ⟨hal-01313530⟩ Plus de détails...
M. Farge, K. Schneider, Olivier Pannekoucke, R. Nguyen Van Yen. Multiscale representations: fractals, self-similar random processes and wavelets. H.J. Fernando. Handbook of Environmental Fluid Dynamics, II, Taylor and Francis, pp.311-332, 2013. ⟨hal-01313530⟩
Katsunori Yoshimatsu, Naoya Okamoto, Yasuhiro Kawahara, Kai Schneider, Marie Farge. Coherent vorticity and current density simulation of three-dimensional magnetohydrodynamic turbulence using orthogonal wavelets. Geophysical and Astrophysical Fluid Dynamics, 2013, 107 (1-2), pp.73-92. ⟨10.1080/03091929.2012.654790⟩. ⟨hal-01032369⟩ Plus de détails...
A simulation method to track the time evolution of coherent vorticity and current density, called coherent vorticity and current density simulation (CVCS), is developed for three-dimensional (3D) incompressible magnetohydrodynamic (MHD) turbulence. The vorticity and current density fields are, respectively, decomposed at each time step into two orthogonal components, the coherent and incoherent fields, using an orthogonal wavelet representation. Each of the coherent fields is reconstructed from the wavelet coefficients whose modulus is larger than a threshold, while their incoherent counterparts are obtained from the remaining coefficients. The two threshold values depend on the instantaneous kinetic and magnetic enstrophies. The induced coherent velocity and magnetic fields are computed from the coherent vorticity and current density using the Biot-Savart kernel. In order to compute the flow evolution, one should retain not only the coherent wavelet coefficients but also their neighbors in wavelet space, and the set of those additional coefficients is called the safety zone. CVCS is performed for 3D forced incompressible homogeneous MHD turbulence without mean magnetic field for a magnetic Prandtl number equal to unity and with 256^3 grid points. The quality of CVCS is assessed by comparing the results with a direct numerical simulation. It is found that CVCS with the safety zone well preserves the statistical predictability of the turbulent flow with a reduced number of degrees of freedom. CVCS is also compared with a Fourier truncated simulation using a spectral cutoff filter where the number of retained Fourier modes is similar to the number of the wavelet coefficients retained by CVCS. It is shown that the wavelet representation is more suitable than the Fourier representation, especially concerning the probability density functions of vorticity and current density.
Katsunori Yoshimatsu, Naoya Okamoto, Yasuhiro Kawahara, Kai Schneider, Marie Farge. Coherent vorticity and current density simulation of three-dimensional magnetohydrodynamic turbulence using orthogonal wavelets. Geophysical and Astrophysical Fluid Dynamics, 2013, 107 (1-2), pp.73-92. ⟨10.1080/03091929.2012.654790⟩. ⟨hal-01032369⟩
Journal: Geophysical and Astrophysical Fluid Dynamics
The spatiotemporal self-organization of viscoresistive magnetohydrodynamics (MHD) in a toroidal geometry is studied. Curl-free toroidal magnetic and electric fields are imposed. It is observed in our simulations that a flow is generated, which evolves from dominantly poloidal to toroidal when the Lundquist numbers are increased. It is shown that this toroidal organization of the flow is consistent with the tendency of the velocity field to align with the magnetic field. Up-down asymmetry of the geometry causes the generation of a non-zero toroidal angular momentum.
Jorge Morales, Wouter J.T. Bos, Kai Schneider, David Montgomery. Intrinsic rotation of toroidally confined magnetohydrodynamics. Physical Review Letters, 2012, 109 (175002), pp.175002. ⟨10.1103/PhysRevLett.109.175002⟩. ⟨hal-00733093⟩
Philippe Meliga, Gregory Pujals, Eric Serre. Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability. Physics of Fluids, 2012, 24, pp.061701. ⟨10.1063/1.4724211⟩. ⟨hal-01061797⟩ Plus de détails...
We use adjoint-based gradients to analyze the sensitivity of turbulent wake past a D-shaped cylinder at Re = 13000. We assess the ability of a much smaller control cylinder in altering the shedding frequency, as predicted by the eigenfrequency of the most unstable global mode to the mean flow. This allows performing beforehand identification of the sensitive regions, i.e., without computing the actually controlled states. Our results obtained in the frame of 2-D, unsteady Reynolds-averaged Navier-Stokes compare favorably with experimental data reported by Parezanović and Cadot [J. Fluid Mech.693, 115 (2012)] and suggest that the control cylinder acts primarily through a local modification of the mean flow profiles.
Philippe Meliga, Gregory Pujals, Eric Serre. Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability. Physics of Fluids, 2012, 24, pp.061701. ⟨10.1063/1.4724211⟩. ⟨hal-01061797⟩
Raimund Burger, Ricardo Ruiz-Baier, Kai Schneider, Hector Torres. A multiresolution method for the simulation of sedimentation in inclined channels. International Journal of Numerical Analysis and Modeling, 2012, 9 (3), pp.479-504. ⟨hal-01032442⟩ Plus de détails...
An adaptive multiresolution scheme is proposed for the numerical solution of a spatially two-dimensional model of sedimentation of suspensions of small solid particles dispersed in a viscous fluid. This model consists in a version of the Stokes equations for incompressible fluid flow coupled with a hyperbolic conservation law for the local solids concentration. We study the process in an inclined, rectangular closed vessel, a configuration that gives rise a well-known increase of settling rates (compared with a vertical vessel) known as the "Boycott effect". Sharp fronts and discontinuities in the concentration field are typical features of sedimentation phenomena. This solution behavior calls for locally refined meshes to concentrate computational effort on zones of strong variation. The spatial discretization presented herein is naturally based on a finite volume (FV) formulation for the Stokes problem including a pressure stabilization technique, while a Godunov-type scheme endowed with a fully adaptive multiresolution (MR) technique is applied to capture the evolution of the concentration field, which in addition induces an important speed-up of CPU time and savings in memory requirements. Numerical simulations illustrate that the proposed scheme is robust and allows for substantial reductions in computational effort while the computations remain accurate and stable.
Raimund Burger, Ricardo Ruiz-Baier, Kai Schneider, Hector Torres. A multiresolution method for the simulation of sedimentation in inclined channels. International Journal of Numerical Analysis and Modeling, 2012, 9 (3), pp.479-504. ⟨hal-01032442⟩
Journal: International Journal of Numerical Analysis and Modeling
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, 2012, 52 (5-6), pp.401-405. ⟨10.1002/ctpp.201210023⟩. ⟨hal-00848473⟩ Plus de détails...
The SOLEDGE suite of codes has been specially designed to model the transition region from the hot core plasma to the first wall of tokamak, through the Last Closed Flux Surface (LCFS). It is designed to model electrostatic fluid turbulence for an isothermal plasma or for a plasma with temperature variations. Dedicated discretization algorithms have been implemented to handle equations for ion density, electron/ion temperatures and parallel momentum, both for the realistic cross-section of a diverted tokamak and for a three-dimensional cylindrical annulus. The efficient penalization method introduced in Ref. [5] has been implemented, allowing straightforward handling of solid obstacles by treating them as sink regions corresponding to strong plasma recombination in the solid state material. The SOLEDGE capability is exemplified here by simulating two equilibria: (i) a 3D cylindrical annulus and (ii) the cross-section of a diverted tokamak. In the annulus, the analysis of the impact of a secondary discrete limiter shows that the toroidal symmetry usually assumed for density and Mach profiles is broken. The density exhibits significant variations in the toroidal direction that extend over a large region of the scrape-off layer where magnetic field lines are connected to a secondary limiter. In the diverted geometry, computations show a transition from subsonic to supersonic flow in the vicinity of the X-point that is related to the location of particle sources and sinks between the edge connected region and the divertor region.
Eric Serre, Hugo Bufferand, A. Paredes, Frédéric Schwander, Guido Ciraolo, et al.. Numerical modeling of the impact of geometry and wall components on transport in the tokamak edge. Contributions to Plasma Physics, 2012, 52 (5-6), pp.401-405. ⟨10.1002/ctpp.201210023⟩. ⟨hal-00848473⟩
Philippe Meliga, François Gallaire, Jean-Marc Chomaz. A weakly nonlinear mechanism for mode selection in swirling jets. Journal of Fluid Mechanics, 2012, 699, pp.216-262. ⟨10.1017/jfm.2012.93⟩. ⟨hal-01067663⟩ Plus de détails...
Global linear and nonlinear bifurcation analysis is used to revisit the spiral vortex breakdown of nominally axisymmetric swirling jets. For the parameters considered herein, stability analyses single out two unstable linear modes of azimuthal wavenumber m=1 and m=2, bifurcating from the axisymmetric breakdown solution. These modes are interpreted in terms of spiral perturbations wrapped around and behind the axisymmetric bubble, rotating in time in the same direction as the swirling flow but winding in space in the opposite direction. Issues are addressed regarding the role of these modes with respect to the existence, mode selection and internal structure of vortex breakdown, as assessed from the three-dimensional direct numerical simulations of Ruith et al. (J. Fluid Mech., vol. 486, 2003, pp. 331-378). The normal form describing the leading-order nonlinear interaction between modes is computed and analysed. It admits two stable solutions corresponding to pure single and double helices. At large swirl, the axisymmetric solution bifurcates to the double helix which remains the only stable solution. At low and moderate swirl, it bifurcates first to the single helix, and subsequently to the double helix through a series of subcritical bifurcations yielding hysteresis over a finite range of Reynolds numbers, the estimated bifurcation threshold being in good agreement with that observed in the direct numerical simulations. Evidence is provided that this selection is not to be ascribed to classical mean flow corrections induced by the existence of the unstable modes, but to a non-trivial competition between harmonics. Because the frequencies of the leading modes approach a strong 2:1 resonance, an alternative normal form allowing interactions between the m=2 mode and the first harmonics of the m=1 mode is computed and analysed. It admits two stable solutions, the double helix already identified in the non-resonant case, and a single helix differing from that observed in the non-resonant case only by the presence of a slaved, phase-locked harmonic deformation. On behalf of the finite departure from the 2:1 resonance, the amplitude of the slaved harmonic is however low, and the effect of the resonance on the bifurcation structure is merely limited to a reduction of the hysteresis range.
Philippe Meliga, François Gallaire, Jean-Marc Chomaz. A weakly nonlinear mechanism for mode selection in swirling jets. Journal of Fluid Mechanics, 2012, 699, pp.216-262. ⟨10.1017/jfm.2012.93⟩. ⟨hal-01067663⟩
Ouafa Bouloumou, Eric Serre, Patrick Bontoux, J. Fröhlich. A 3D pseudo-spectral low Mach-number solver for buoyancy driven flows with large temperature differences. Computers and Fluids, 2012, 66, pp.107-120. ⟨10.1016/j.compfluid.2012.05.014⟩. ⟨hal-00834130⟩ Plus de détails...
A three-dimensional spectral method based on a Chebyshev/Chebyshev/Fourier discretization is proposed to integrate the Navier-Stokes equations for natural convection flow with large temperature differences under the low Mach-number approximation. The generalized Stokes problem arising from the time discretization by a second-order semi-implicit scheme is solved by a preconditioned iterative Uzawa algorithm. The spectrally convergent algorithm is validated on well-documented Boussinesq and non-Boussinesq benchmarks. Finally, non-Boussineq convection is investigated in a tall differentially heated cavity of aspect ratio 8 with one homogeneous direction. The technique is shown to be efficient in terms of computing performances and accuracy. The study brings new stability results evidencing 3D effects compared to both Boussinesq convection and former two-dimensional non-Boussinesq solutions. In particular, for Ra ⩾ 105 two-dimensional solutions are shown to be unstable with respect to three-dimensional perturbations. A Görtler-type instability grows in the region of the curved streamlines at both ends of the cavity and gives rise to 3D steady and oscillatory solutions. At higher Rayleigh numbers, these vortices eventually interact with a boundary layer instability leading to complex dynamics with multiple steady and unsteady stable solutions.
Ouafa Bouloumou, Eric Serre, Patrick Bontoux, J. Fröhlich. A 3D pseudo-spectral low Mach-number solver for buoyancy driven flows with large temperature differences. Computers and Fluids, 2012, 66, pp.107-120. ⟨10.1016/j.compfluid.2012.05.014⟩. ⟨hal-00834130⟩
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Incorporating Darcy's law for pure solvent flow through porous tubes: Asymptotic solution and numerical simulations. AIChE Journal, 2012, 58 (7), pp.2030-2044. ⟨10.1002/aic.13823⟩. ⟨hal-01032148⟩ Plus de détails...
A generalized solution for pressure-driven, incompressible, Newtonian flow in a porous tubular membrane is challenging due to the coupling between the transmembrane pressure and velocity. To date, all analytical solutions require simplifications such as neglecting the coupling between the transmembrane pressure and velocity, assuming the form of the velocity fields, or expanding in powers of parameters involving the tube length. Moreover, previous solutions have not been validated with comparison to direct numerical simulation (DNS). We comprehensively revisit the problem to present a robust analytical solution incorporating Darcy's law on the membrane. We make no assumptions about the tube length or form of the velocity fields. The analytic solution is validated with detailed comparison to DNSs, including cases of axial flow exhaustion and cross flow reversal. We explore the validity of typical assumptions used in modeling porous tube flow and present a solution for porous channels in Supporting Information.
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Incorporating Darcy's law for pure solvent flow through porous tubes: Asymptotic solution and numerical simulations. AIChE Journal, 2012, 58 (7), pp.2030-2044. ⟨10.1002/aic.13823⟩. ⟨hal-01032148⟩
Raimund Buerger, Ricardo Ruiz-Baier, Kai Schneider, Ă Hector Torres. A MULTIRESOLUTION METHOD FOR THE SIMULATION OF SEDIMENTATION IN INCLINED ă CHANNELS. International Journal of Numerical Analysis and Modeling, 2012, 9 (3), pp.479-504. ⟨hal-01464735⟩ Plus de détails...
An adaptive multiresolution scheme is proposed for the numerical ă solution of a spatially two-dimensional model of sedimentation of ă suspensions of small solid particles dispersed in a viscous fluid. This ă model consists in a version of the Stokes equations for incompressible ă fluid flow coupled with a hyperbolic conservation law for the local ă solids concentration. We study the process in an inclined, rectangular ă closed vessel, a configuration that gives rise a well-known increase of ă settling rates (compared with a vertical vessel) known as the ``Boycott ă effect''. Sharp fronts and discontinuities in the concentration field ă are typical features of sedimentation phenomena. This solution behavior ă calls for locally refined meshes to concentrate computational effort on ă zones of strong variation. The spatial discretization presented herein ă is naturally based on a finite volume (FV) formulation for the Stokes ă problem including a pressure stabilization technique, while a ă Godunov-type scheme endowed with a fully adaptive multiresolution (MR) ă technique is applied to capture the evolution of the concentration ă field, which in addition induces an important speed-up of CPU time and ă savings in memory requirements. Numerical simulations illustrate that ă the proposed scheme is robust and allows for substantial reductions in ă computational effort while the computations remain accurate and stable.
Raimund Buerger, Ricardo Ruiz-Baier, Kai Schneider, Ă Hector Torres. A MULTIRESOLUTION METHOD FOR THE SIMULATION OF SEDIMENTATION IN INCLINED ă CHANNELS. International Journal of Numerical Analysis and Modeling, 2012, 9 (3), pp.479-504. ⟨hal-01464735⟩
Journal: International Journal of Numerical Analysis and Modeling
J. X. Sheng, A. Ysasi, Dmitry Kolomenskiy, E. Kanso, M. Nitsche, et al.. Simulating vortex wakes of flapping plates. Childress S. and all. Natural Locomotion in Fluids and on Surfaces: Swimming, Flying, and Sliding, Springer Science+Business Media, pp.255-262, 2012, The IMA Volumes in Mathematics and its Applications, 978-1-4614-3996-7. ⟨10.1007/978-1-4614-3997-4_21⟩. ⟨hal-01032453⟩ Plus de détails...
We compare different models to simulate two-dimensional vortex wakes behind oscillating plates. In particular, we compare solutions using a vortex sheet model and the simpler Brown-Michael model to solutions of the full Navier-Stokes equations obtained using a penalization method. The goal is to determine whether simpler models can be used to obtain good approximations to the form of the wake and the induced forces on the body.
J. X. Sheng, A. Ysasi, Dmitry Kolomenskiy, E. Kanso, M. Nitsche, et al.. Simulating vortex wakes of flapping plates. Childress S. and all. Natural Locomotion in Fluids and on Surfaces: Swimming, Flying, and Sliding, Springer Science+Business Media, pp.255-262, 2012, The IMA Volumes in Mathematics and its Applications, 978-1-4614-3996-7. ⟨10.1007/978-1-4614-3997-4_21⟩. ⟨hal-01032453⟩
Frank G. Jacobitz, Kai Schneider, Wouter J.T. Bos, Marie Farge. On helical multiscale characterization of homogeneous turbulence. Journal of Turbulence, 2012, 13, pp.N35. ⟨10.1080/14685248.2012.711476⟩. ⟨hal-00780153⟩ Plus de détails...
Frank G. Jacobitz, Kai Schneider, Wouter J.T. Bos, Marie Farge. On helical multiscale characterization of homogeneous turbulence. Journal of Turbulence, 2012, 13, pp.N35. ⟨10.1080/14685248.2012.711476⟩. ⟨hal-00780153⟩
Romain Nguyen van Yen, Marie Farge, Kai Schneider. Scale-wise coherent vorticity extraction for conditional statistical modeling of homogeneous isotropic two-dimensional turbulence. Physica D: Nonlinear Phenomena, 2012, 241 (3), pp.186-201. ⟨10.1016/j.physd.2011.05.022⟩. ⟨hal-01115481⟩ Plus de détails...
Classical statistical theories of turbulence have shown their limitations, in that they cannot predict much more than the energy spectrum in an idealized setting of statistical homogeneity and stationarity. We explore the applicability of a conditional statistical modeling approach: can we sort out what part of the information should be kept, and what part should be modeled statistically, or, in other words, "dissipated"? Our mathematical framework is the initial value problem for the two-dimensional (2D) Euler equations, which we approximate numerically by solving the 2D Navier-Stokes equations in the vanishing viscosity limit. In order to obtain a good approximation of the inviscid dynamics, we use a spectral method and a resolution going up to 8192(2). We introduce a macroscopic concept of dissipation, relying on a split of the flow between coherent and incoherent contributions: the coherent flow is constructed from the large wavelet coefficients of the vorticity field, and the incoherent flow from the small ones. In previous work, a unique threshold was applied to all wavelet coefficients, while here we also consider the effect of a scale by scale thresholding algorithm, called scale-wise coherent vorticity extraction. We study the statistical properties of the coherent and incoherent vorticity fields, and the transfers of enstrophy between them, and then use these results to propose, within a maximum entropy framework, a simple model for the incoherent vorticity. In the framework of this model, we show that the flow velocity can be predicted accurately in the L-2 norm for about 10 eddy turnover times. (C) 2011 Elsevier B.V. All rights reserved.
Romain Nguyen van Yen, Marie Farge, Kai Schneider. Scale-wise coherent vorticity extraction for conditional statistical modeling of homogeneous isotropic two-dimensional turbulence. Physica D: Nonlinear Phenomena, 2012, 241 (3), pp.186-201. ⟨10.1016/j.physd.2011.05.022⟩. ⟨hal-01115481⟩
Julien Favier, Alfredo Pinelli, Ugo Piomelli. Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers. Comptes Rendus Mécanique, 2012, 340 (1-2), pp.107-114. ⟨10.1016/j.crme.2011.11.004⟩. ⟨hal-00941404⟩ Plus de détails...
The influence of spanwise geometrical undulations of the leading edge of an infinite wing is investigated numerically at low Reynolds number, in the context of passive separation control and focusing on the physical mechanisms involved. Inspired by the tubercles of the humpback whale flippers, the wavy leading edge is modeled using a spanwise sinusoidal function whose amplitude and wavelength constitute the parameters of control. A direct numerical simulation is performed on a NACA0020 wing profile in a deep stall configuration (α=20°α=20°), with and without the presence of the leading edge waviness. The complex solid boundaries obtained by varying the sinusoidal shape of the leading edge are modeled using an immersed boundary method (IBM) recently developed by the authors [Pinelli et al., J. Comput. Phys. 229 (2010) 9073-9091]. A particular set of wave parameters is found to change drastically the topology of the separated zone, which becomes dominated by streamwise vortices generated from the sides of the leading edge bumps. A physical analysis is carried out to explain the mechanism leading to the generation of these coherent vortical structures. The role they play in the control of boundary layer separation is also investigated, in the context of the modifications of the hydrodynamic performances which have been put forward in the literature in the last decade.
Julien Favier, Alfredo Pinelli, Ugo Piomelli. Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers. Comptes Rendus Mécanique, 2012, 340 (1-2), pp.107-114. ⟨10.1016/j.crme.2011.11.004⟩. ⟨hal-00941404⟩
Benjamin Kadoch, Dmitry Kolomenskiy, Philippe Angot, Kai Schneider. A volume penalization method for incompressible flows and scalar advection-diffusion with moving obstacles. Journal of Computational Physics, 2012, 231 (12), pp.4365-4383. ⟨10.1016/j.jcp.2012.01.036⟩. ⟨hal-01032208⟩ Plus de détails...
A volume penalization method for imposing homogeneous Neumann boundary conditions in advection-diffusion equations is presented. Thus complex geometries which even may vary in time can be treated efficiently using discretizations on a Cartesian grid. A mathematical analysis of the method is conducted first for the one-dimensional heat equation which yields estimates of the penalization error. The results are then confirmed numerically in one and two space dimensions. Simulations of two-dimensional incompressible flows with passive scalars using a classical Fourier pseudo-spectral method validate the approach for moving obstacles. The potential of the method for real world applications is illustrated by simulating a simplified dynamical mixer where for the fluid flow and the scalar transport no-slip and no-flux boundary conditions are imposed, respectively.
Benjamin Kadoch, Dmitry Kolomenskiy, Philippe Angot, Kai Schneider. A volume penalization method for incompressible flows and scalar advection-diffusion with moving obstacles. Journal of Computational Physics, 2012, 231 (12), pp.4365-4383. ⟨10.1016/j.jcp.2012.01.036⟩. ⟨hal-01032208⟩
Michael Wilczek, Benjamin Kadoch, Kai Schneider, Rudolf Friedrich, Marie Farge. Conditional vorticity budget of coherent and incoherent flow contributions in fully developed homogeneous isotropic turbulence. Physics of Fluids, 2012, 24 (3), pp.035108. ⟨10.1063/1.3694807⟩. ⟨hal-01455124⟩ Plus de détails...
We investigate the conditional vorticity budget of fully developed three-dimensional homogeneous isotropic turbulence with respect to coherent and incoherent flow contributions. The coherent vorticity extraction based on orthogonal wavelets allows to decompose the vorticity field into coherent and incoherent contributions, of which the latter are noise-like. The impact of the vortex structures observed in fully developed turbulence on statistical balance equations is quantified considering the conditional vorticity budget. The connection between the basic structures present in the flow and their statistical implications is thereby assessed. The results are compared to those obtained for large-and small-scale contributions using a Fourier decomposition , which reveals pronounced differences.
Michael Wilczek, Benjamin Kadoch, Kai Schneider, Rudolf Friedrich, Marie Farge. Conditional vorticity budget of coherent and incoherent flow contributions in fully developed homogeneous isotropic turbulence. Physics of Fluids, 2012, 24 (3), pp.035108. ⟨10.1063/1.3694807⟩. ⟨hal-01455124⟩
Romain Nguyen van Yen, Nicolas Fedorczak, F. Brochard, Gildas Bonhomme, Kai Schneider, et al.. Tomographic reconstruction of tokamak plasma light emission from single image using wavelet-vaguelette decomposition. Nuclear Fusion, 2012, 52 (1), pp.013005. ⟨10.1088/0029-5515/52/1/013005⟩. ⟨hal-01032416⟩ Plus de détails...
Images acquired by cameras installed in tokamaks are difficult to interpret because the three-dimensional structure of the plasma is flattened in a non-trivial way. Nevertheless, taking advantage of the slow variation of the fluctuations along magnetic field lines, the optical transformation may be approximated by a generalized Abel transform, for which we propose an inversion technique based on the wavelet-vaguelette decomposition. After validation of the new method using an academic test case and numerical data obtained with the Tokam 2D code, we present an application to an experimental movie obtained in the tokamak Tore Supra. A comparison with a classical regularization technique for ill-posed inverse problems, the singular value decomposition, allows us to assess the efficiency. The superiority of the wavelet-vaguelette technique is reflected in preserving local features, such as blobs and fronts, in the denoised emissivity map.
Romain Nguyen van Yen, Nicolas Fedorczak, F. Brochard, Gildas Bonhomme, Kai Schneider, et al.. Tomographic reconstruction of tokamak plasma light emission from single image using wavelet-vaguelette decomposition. Nuclear Fusion, 2012, 52 (1), pp.013005. ⟨10.1088/0029-5515/52/1/013005⟩. ⟨hal-01032416⟩
Pierre Magnico. Ion size effects on electric double layers and ionic transport through ion-exchange membrane systems. Journal of Membrane Science, 2012, 415, pp.412-423. ⟨10.1016/j.memsci.2012.05.025⟩. ⟨hal-00968166⟩ Plus de détails...
The density function theory is used to study the density profiles and the transport properties of an ion-exchange membrane system submitted to an electric potential drop. As the ionic density increases, hard sphere interaction between ions becomes dominant and the ion size must be taken into account. The results show that the density distribution and the transport properties depend on the bulk electrolyte density. At equilibrium the charge inside the electric double layer (EDL) adjacent to the membrane decreases and the membrane electric potential increases as the bulk density increases. For high bulk density of unsymmetric electrolyte, secondary charge layers are observed inside the EDL. In the membrane the anion-density-to-bulk-density ratio increases when the bulk density increases from small to moderate values owing to the membrane potential increase. But it decreases abruptly at high bulk density values owing to the increase of the non-ideal electrostatic interaction. At a given electric potential drop, the current/voltage curves follow the variation of this ratio with respect to the bulk density at equilibrium. As the current density approaches the limiting one, the amplitude of the secondary charge layers decreases and the EDL thickness increases.
Pierre Magnico. Ion size effects on electric double layers and ionic transport through ion-exchange membrane systems. Journal of Membrane Science, 2012, 415, pp.412-423. ⟨10.1016/j.memsci.2012.05.025⟩. ⟨hal-00968166⟩
M Wilczek, Benjamin Kadoch, K. Schneider, R. Friedrich, M. Farge. Wavelet Analysis of the Conditional Vorticity Budget in Fully Developed Homogeneous Isotropic Turbulence. Journal of Physics: Conference Series, 2011, 318 (6), pp.062024. ⟨10.1088/1742-6596/318/6/062024⟩. ⟨hal-02535213⟩ Plus de détails...
M Wilczek, Benjamin Kadoch, K. Schneider, R. Friedrich, M. Farge. Wavelet Analysis of the Conditional Vorticity Budget in Fully Developed Homogeneous Isotropic Turbulence. Journal of Physics: Conference Series, 2011, 318 (6), pp.062024. ⟨10.1088/1742-6596/318/6/062024⟩. ⟨hal-02535213⟩
Benjamin Kadoch, D Del-Castillo-Negrete, W Bos, K. Schneider. Influence of flow topology on Lagrangian statistics in two-dimensional turbulence. Journal of Physics: Conference Series, 2011, 318 (5), pp.052032. ⟨10.1088/1742-6596/318/5/052032⟩. ⟨hal-02535093⟩ Plus de détails...
Benjamin Kadoch, D Del-Castillo-Negrete, W Bos, K. Schneider. Influence of flow topology on Lagrangian statistics in two-dimensional turbulence. Journal of Physics: Conference Series, 2011, 318 (5), pp.052032. ⟨10.1088/1742-6596/318/5/052032⟩. ⟨hal-02535093⟩
Benjamin Kadoch, Diego del Castillo Negrete, Wouter J.T. Bos, Kai Schneider. Lagrangian statistics and flow topology in forced two-dimensional turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2011, 83, pp.036314. ⟨10.1103/PhysRevE.83.036314⟩. ⟨hal-00647805⟩ Plus de détails...
A study of the relationship between Lagrangian statistics and flow topology in fluid turbulence is presented. The topology is characterized using the Weiss criterion, which provides a conceptually simple tool to partition the flow into topologically different regions: elliptic (vortex dominated), hyperbolic (deformation dominated), and intermediate (turbulent background). The flow corresponds to forced two-dimensional Navier-Stokes turbulence in doubly periodic and circular bounded domains, the latter with no-slip boundary conditions. In the double periodic domain, the probability density function (pdf) of the Weiss field exhibits a negative skewness consistent with the fact that in periodic domains the flow is dominated by coherent vortex structures. On the other hand, in the circular domain, the elliptic and hyperbolic regions seem to be statistically similar. We follow a Lagrangian approach and obtain the statistics by tracking large ensembles of passively advected tracers. The pdfs of residence time in the topologically different regions are computed introducing the Lagrangian Weiss field, i.e., the Weiss field computed along the particles' trajectories. In elliptic and hyperbolic regions, the pdfs of the residence time have self-similar algebraic decaying tails. In contrast, in the intermediate regions the pdf has exponential decaying tails. The conditional pdfs (with respect to the flow topology) of the Lagrangian velocity exhibit Gaussian-like behavior in the periodic and in the bounded domains. In contrast to the freely decaying turbulence case, the conditional pdfs of the Lagrangian acceleration in forced turbulence show a comparable level of intermittency in both the periodic and the bounded domains. The conditional pdfs of the Lagrangian curvature are characterized, in all cases, by self-similar power-law behavior with a decay exponent of order -2.
Benjamin Kadoch, Diego del Castillo Negrete, Wouter J.T. Bos, Kai Schneider. Lagrangian statistics and flow topology in forced two-dimensional turbulence. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2011, 83, pp.036314. ⟨10.1103/PhysRevE.83.036314⟩. ⟨hal-00647805⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Shinpei Futatani, Wouter J.T. Bos, Diego del Castillo Negrete, Kai Schneider, Sadruddin Benkadda, et al.. Coherent vorticity extraction in resistive drift-wave turbulence: Comparison of orthogonal wavelets versus proper orthogonal decomposition. Comptes Rendus. Physique, 2011, 12, pp.123-131. ⟨10.1016/j.crhy.2010.12.004⟩. ⟨hal-00647820⟩ Plus de détails...
We assess two techniques for extracting coherent vortices out of turbulent flows: the wavelet based Coherent Vorticity Extraction (CVE) and the Proper Orthogonal Decomposition (POD). The former decomposes the flow field into an orthogonal wavelet representation and subsequent thresholding of the coefficients allows one to split the flow into organized coherent vortices with non-Gaussian statistics and an incoherent random part which is structureless. POD is based on the singular value decomposition and decomposes the flow into basis functions which are optimal with respect to the retained energy for the ensemble average. Both techniques are applied to direct numerical simulation data of two-dimensional drift-wave turbulence governed by Hasegawa-Wakatani equation, considering two limit cases: the quasi-hydrodynamic and the quasi-adiabatic regimes. The results are compared in terms of compression rate, retained energy, retained enstrophy and retained radial flux, together with the enstrophy spectrum and higher order statistics.
Shinpei Futatani, Wouter J.T. Bos, Diego del Castillo Negrete, Kai Schneider, Sadruddin Benkadda, et al.. Coherent vorticity extraction in resistive drift-wave turbulence: Comparison of orthogonal wavelets versus proper orthogonal decomposition. Comptes Rendus. Physique, 2011, 12, pp.123-131. ⟨10.1016/j.crhy.2010.12.004⟩. ⟨hal-00647820⟩
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, 2011, 415 (1), pp.S574-S578. ⟨10.1016/j.jnucmat.2010.12.318⟩. ⟨hal-00848528⟩ Plus de détails...
We are interested here in modelling the electron and ion temperature fields, Te and Ti respectively, in order to understand the main trends that govern the ratio Ti/Te that is being better documented in the SOL with RFA probes and . The experimental evidence gathered from several devices indicates that this temperature ratio significantly exceeds unity in most data sets that have been analysed, including measurements in the SOL of limiter devices like Tore Supra. Several issues of interest have been addressed with this version of the SOLEDGE-2D code. First, we have analysed the width of the SOL heat channels to the wall components and compared these values to analytical expressions. The key control mechanism of the width of the SOL heat channel is given by a balance between the sheath boundary conditions and the transverse transport. More advanced simulations address the interplay between the edge and SOL plasma allowing one to recover regimes with Ti/Te > 1.
Livia Isoardi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, Frédéric Schwander, et al.. 2D modelling of electron and ion temperature in the plasma edge and SOL. Journal of Nuclear Materials, 2011, 415 (1), pp.S574-S578. ⟨10.1016/j.jnucmat.2010.12.318⟩. ⟨hal-00848528⟩
Matthieu Minguez, Christophe Brun, Richard Pasquetti, Eric Serre. Experimental and high-order LES analysis of the flow in near-wall region of a square cylinder. International Journal of Heat and Fluid Flow, 2011, 32 (3), pp.558-566. ⟨10.1016/j.ijheatfluidflow.2011.03.009⟩. ⟨hal-01299962⟩ Plus de détails...
A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed at the ERCOFTAC Reynolds number Re = U∞D/ν = 21,400, where U∞ is the inflow velocity and D the cylinder height. Complementary Laser Doppler Velocimetry (LDV) and high-order large-eddy simulations (LES) approaches, based on a spectral vanishing technique (SVV-LES), provide a comprehensive data base including both instantaneous data and post-processed statistics. Beyond these results, an achievement of the paper is to investigate the coherent structures developing on the sides and in the wake of the cylinder with a special focus on the flow features in the near-wall region. The flow is found to separate at the leading edge of the cylinder with the occurence of three-dimensional Kelvin–Helmholtz (KH) pairings localized in the separating shear layer. The interaction between these KH vortical structures and Von Kármán vortex shedding (VK) in the near wake is discussed based on both visualisations and frequency analysis. In particular, signatures of VK and KH vortical structures are found on velocity time samples.
Matthieu Minguez, Christophe Brun, Richard Pasquetti, Eric Serre. Experimental and high-order LES analysis of the flow in near-wall region of a square cylinder. International Journal of Heat and Fluid Flow, 2011, 32 (3), pp.558-566. ⟨10.1016/j.ijheatfluidflow.2011.03.009⟩. ⟨hal-01299962⟩
Journal: International Journal of Heat and Fluid Flow
E. Plaut, Y. Lebranchu, M. Jenny, Eric Serre. Structure and stability of annular sheared channel flows: effects of confinement, curvature and inertial forces - waves. The European Physical Journal B: Condensed Matter and Complex Systems, 2011, 79 (1), pp.35-46. ⟨10.1140/epjb/e2010-10572-3⟩. ⟨hal-01023235⟩ Plus de détails...
The structure and stability of the flows in an annular channel sheared by a rotating lid are investigated experimentally, theoretically and numerically. The channel has a square section, and a small curvature parameter: the ratio Γ of the inter-radii to the mean radius is 9.5%. The sidewalls and the bottom of the channel are integral and can rotate independently of the lid, permitting pure shear, co-rotation and counter-rotation cases. The basic flows obtained at small shear are characterized. In the absence of co-rotation, the centrifugal force linked with the curvature of the system plays an important role, whereas, when co-rotation is fast, the Coriolis force dominates. These basic flows undergo some instabilities when the shear is increased. These instabilities lead to supercritical traveling waves in the pure shear and co-rotation cases, but to weak turbulence in the counter-rotation case. The Reynolds number for the onset of instabilities, constructed with the velocity difference between the lid and bottom at mid-radius, and the height of the channel, increases from 1000 in the counter-rotation case to 1260 in the pure shear case and higher and higher values when co-rotation increases, i.e., when the Coriolis effect increases. The relevance of uni-dimensional Ginzburg-Landau models to describe the dynamics of the waves is studied. The domain of validity of these models turns out to be quite narrow.
E. Plaut, Y. Lebranchu, M. Jenny, Eric Serre. Structure and stability of annular sheared channel flows: effects of confinement, curvature and inertial forces - waves. The European Physical Journal B: Condensed Matter and Complex Systems, 2011, 79 (1), pp.35-46. ⟨10.1140/epjb/e2010-10572-3⟩. ⟨hal-01023235⟩
Journal: The European Physical Journal B: Condensed Matter and Complex Systems
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. Two- and three-dimensional numerical simulations of the clap-fling-sweep of hovering insects. Journal of Fluids and Structures, 2011, 27 (5-6), pp.784-791. ⟨10.1016/j.jfluidstructs.2011.05.002⟩. ⟨hal-01022662⟩ Plus de détails...
The importance of three-dimensional effects for flapping wings is addressed by means of numerical simulation. In particular, the clap-fling-sweep mechanism is examined. The flow at the beginning of the downstroke is shown to be in reasonable agreement with the two-dimensional approximation. After the wings move farther than one chord length apart, three-dimensional effects become essential. Two values of the Reynolds number are considered. At Re=128, the spanwise flow from the wing roots to the wing tips is driven by the centrifugal forces acting on the mass of the fluid trapped in the recirculation bubble behind the wings. It removes the excess of vorticity and delays the periodic vortex shedding. At Re=1400, vortex breakdown occurs past the outer portion of the wings, and multiple vortex filaments are shed into the wake.
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. Two- and three-dimensional numerical simulations of the clap-fling-sweep of hovering insects. Journal of Fluids and Structures, 2011, 27 (5-6), pp.784-791. ⟨10.1016/j.jfluidstructs.2011.05.002⟩. ⟨hal-01022662⟩
Eric Serre, M. Minguez, R., Pasquetti, G.B. Deng, M. Kornhass, et al.. On simulating the turbulent flow around the Ahmed body : A French-German collaborative evaluation of LES and DES. Computers and Fluids, 2011. ⟨hal-01145131⟩ Plus de détails...
Eric Serre, M. Minguez, R., Pasquetti, G.B. Deng, M. Kornhass, et al.. On simulating the turbulent flow around the Ahmed body : A French-German collaborative evaluation of LES and DES. Computers and Fluids, 2011. ⟨hal-01145131⟩
Kai Schneider, Salah Neffaa, Wouter J.T. Bos. A pseudo-spectral method with volume penalisation for magnetohydrodynamic turbulence in confined domains. Computer Physics Communications, 2011, 182 (1), pp.2-7. ⟨10.1016/j.cpc.2010.05.019⟩. ⟨hal-00647827⟩ Plus de détails...
We present a Fourier pseudo-spectral method for solving the resistive magnetohydrodynamic equations of incompressible flow in confined domains. A volume penalisation method allows to take into account boundary conditions and the geometry of the domain. A code validation is presented for the z-pinch test case. Numerical simulations of decaying MHD turbulence in two space dimensions show spontaneous spin-up of the flow in non-axisymmetric geometries, which is reflected by the generation of angular momentum. First results of decaying MHD turbulence in a cylinder illustrate the potential of the new method for three-dimensional simulations.
Kai Schneider, Salah Neffaa, Wouter J.T. Bos. A pseudo-spectral method with volume penalisation for magnetohydrodynamic turbulence in confined domains. Computer Physics Communications, 2011, 182 (1), pp.2-7. ⟨10.1016/j.cpc.2010.05.019⟩. ⟨hal-00647827⟩
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, 2011, 53 (5), pp.054019. ⟨10.1088/0741-3335/53/5/054019⟩. ⟨hal-00848545⟩ Plus de détails...
With a proper choice of a single dimensionless control parameter one describes the transition between subsonic and supersonic flows as a bifurcation. The bifurcation point is characterized by specific properties of the control parameter: the control parameter has a vanishing derivative in space and takes the maximum possible value equal to 1. This method is then applied to the sheath plasma with constant temperatures, allowing one to recover the Bohm boundary condition as well as the location of the point where the bifurcation takes place. This analysis is extended to fronts, rarefaction waves and divertor plasmas. Two cases are found, those where departure from quasineutrality is mandatory to generate a maximum in the variation of the control parameter (sheath and fronts) and those where the physics of the quasineutral plasma can generate such a maximum (rarefaction waves and supersonic flow in divertors). The conditions that are required to recover the Bohm condition, when modelling the wall using the penalization technique, are also addressed and generalized.
Philippe Ghendrih, K. Bodi, Hugo Bufferand, Guillaume Chiavassa, Guido Ciraolo, et al.. Transition to supersonic flows in the edge plasma. Plasma Physics and Controlled Fusion, 2011, 53 (5), pp.054019. ⟨10.1088/0741-3335/53/5/054019⟩. ⟨hal-00848545⟩
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, 2011, 415 (1), pp.S601-S604. ⟨10.1016/j.jnucmat.2010.10.073⟩. ⟨hal-00848536⟩ Plus de détails...
The transition between the core and scrape-off layer of a tokamak corresponds to a marked momentum shear layer, owing to sheath acceleration on limiters which drives near-sonic flows along the plasma magnetic field in the scrape-off layer, and a parallel shear flow instability can possibly be triggered. The possibility of this instability driven by the velocity gradient is investigated numerically, using a minimum model of particle and parallel momentum transport in the edge of a tokamak, in a computational domain modelling a limiter plasma with background turbulence modelled as an effective diffusion. It is found that unstable regions can exist in the vicinity of a limiter, in agreement with experimental findings, when momentum radial transport - and therefore coupling between SOL and core flows - is sufficiently weak. Instability is reinforced by core rotation, and is found to be maximum downstream of the limiter (with respect to the core plasma flow).
Frédéric Schwander, Guillaume Chiavassa, Guido Ciraolo, Philippe Ghendrih, Livia Isoardi, et al.. Parallel shear flow instability in the tokamak edge. Journal of Nuclear Materials, 2011, 415 (1), pp.S601-S604. ⟨10.1016/j.jnucmat.2010.10.073⟩. ⟨hal-00848536⟩
B. Viaud, Eric Serre, Jean-Marc Chomaz. Transition to turbulence through steep global-modes cascade in an open rotating cavity. Journal of Fluid Mechanics, 2011, 688, pp.493-506. ⟨10.1017/jfm.2011.393⟩. ⟨hal-00998000⟩ Plus de détails...
B. Viaud, Eric Serre, Jean-Marc Chomaz. Transition to turbulence through steep global-modes cascade in an open rotating cavity. Journal of Fluid Mechanics, 2011, 688, pp.493-506. ⟨10.1017/jfm.2011.393⟩. ⟨hal-00998000⟩
Katsunori Yoshimatsu, Kai Schneider, Naoya Okamoto, Yasuhiro Kawahara, Marie Farge. Intermittency and geometrical statistics of three-dimensional homogeneous magnetohydrodynamic turbulence: a wavelet viewpoint. Physics of Plasmas, 2011, 18 (9), pp.092304. ⟨10.1063/1.3628637⟩. ⟨hal-01022645⟩ Plus de détails...
Scale-dependent and geometrical statistics of three-dimensional incompressible homogeneous magnetohydrodynamicturbulence without mean magnetic field are examined by means of the orthogonal wavelet decomposition. The flow is computed by direct numerical simulation with a Fourier spectral method at resolution 5123 and a unit magnetic Prandtl number. Scale-dependent second and higher order statistics of the velocity and magnetic fields allow to quantify their intermittency in terms of spatial fluctuations of the energy spectra, the flatness, and the probability distribution functions at different scales. Different scale-dependent relative helicities, e.g., kinetic, cross, and magnetic relative helicities, yield geometrical information on alignment between the different scale-dependent fields. At each scale, the alignment between the velocity and magnetic field is found to be more pronounced than the other alignments considered here, i.e., the scale-dependent alignment between the velocity and vorticity, the scale-dependent alignment between the magnetic field and its vector potential, and the scale-dependent alignment between the magnetic field and the current density. Finally, statistical scale-dependent analyses of both Eulerian and Lagrangian accelerations and the corresponding time-derivatives of the magnetic field are performed. It is found that the Lagrangian acceleration does not exhibit substantially stronger intermittency compared to the Eulerian acceleration, in contrast to hydrodynamic turbulence where the Lagrangian acceleration shows much stronger intermittency than the Eulerian acceleration. The Eulerian time-derivative of the magnetic field is more intermittent than the Lagrangian time-derivative of the magnetic field.
Katsunori Yoshimatsu, Kai Schneider, Naoya Okamoto, Yasuhiro Kawahara, Marie Farge. Intermittency and geometrical statistics of three-dimensional homogeneous magnetohydrodynamic turbulence: a wavelet viewpoint. Physics of Plasmas, 2011, 18 (9), pp.092304. ⟨10.1063/1.3628637⟩. ⟨hal-01022645⟩
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, 2011, 415 (1), pp.S589-S592. ⟨10.1016/j.jnucmat.2010.11.037⟩. ⟨hal-00848483⟩ Plus de détails...
A series of experiments dedicated to the determination of the ballooning nature of the edge and SOL transport has been achieved on Tore Supra and , proposing a quantitative characterization of the radial flux that enters the SOL. The aim of this paper is to back up the interpretation of these probe flow measurements making use of SOLEDGE-2D code. In particular, this fluid code allows one to study density and parallel momentum transport in a 2D geometry including edge and SOL region. Moreover, thanks to an appropriate numerical technique recently proposed and , SOLEDGE-2D code is also able to deal with a complex geometry of plasma facing components including main and secondary limiters.
Hugo Bufferand, Guido Ciraolo, Livia Isoardi, Guillaume Chiavassa, Frédéric Schwander, et al.. Applications of SOLEDGE-2D code to complex SOL configurations and analysis of Mach probe measurements. Journal of Nuclear Materials, 2011, 415 (1), pp.S589-S592. ⟨10.1016/j.jnucmat.2010.11.037⟩. ⟨hal-00848483⟩
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, 2011, 415 (1), pp.S579-S583. ⟨10.1016/j.jnucmat.2010.12.247⟩. ⟨hal-00848532⟩ Plus de détails...
Isoardi et al. [1] recently proposed a penalization technique to model solid plasma facing components that treats a solid obstacle as a sink region corresponding to the strong plasma recombination in the solid state material. A major advantage of this approach is that it produces a system that can be solved in an obstacle free domain, thus allowing the use of powerful numerical algorithms. Such a technique implemented in a minimal transport model for ionic density and parallel momentum appeared to exhibit a Mach-1 transition at the boundary layer between the plasma presheath and the limiter region. In this paper, we reconsider this result by analysing the physics of detached plasmas that are governed both by strong recombination and plasma pressure decrease, as imposed by the penalization technique within the limiter region. The analysis provides a unique control parameter A=Γcsmi/ΠA=Γcsmi/Π (Γ being the parallel particles flux, cs the sound speed, mi the ionic mass and Π the total plasma pressure) that allows one to understand the results of the penalization technique for the Mach-1 transition.
A. Paredes, Eric Serre, Livia Isoardi, Guillaume Chiavassa, Guido Ciraolo, et al.. Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique. Journal of Nuclear Materials, 2011, 415 (1), pp.S579-S583. ⟨10.1016/j.jnucmat.2010.12.247⟩. ⟨hal-00848532⟩
Romain Nguyen van Yen, Marie Farge, Kai Schneider. Energy dissipating structures produced by walls in two-dimensional flows at vanishing viscosity. Physical Review Letters, 2011, 106, pp.184502. ⟨10.1103/PhysRevLett.106.184502⟩. ⟨hal-01022604⟩ Plus de détails...
We perform numerical experiments of a dipole crashing into a wall, a generic event in two-dimensional incompressible flows with solid boundaries. The Reynolds number (Re) is varied from 985 to 7880, and no-slip boundary conditions are approximated by Navier boundary conditions with a slip length proportional to Re(-1). Energy dissipation is shown to first set up within a vorticity sheet of thickness proportional to Re(-1) in the neighborhood of the wall, and to continue as this sheet rolls up into a spiral and detaches from the wall. The energy dissipation rate integrated over these regions appears to converge towards Re-independent values, indicating the existence of energy dissipating structures that persist in the vanishing viscosity limit.
Romain Nguyen van Yen, Marie Farge, Kai Schneider. Energy dissipating structures produced by walls in two-dimensional flows at vanishing viscosity. Physical Review Letters, 2011, 106, pp.184502. ⟨10.1103/PhysRevLett.106.184502⟩. ⟨hal-01022604⟩
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C S Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, 2011, 415, ⟨10.1016/j.jnucmat.2010.12.035⟩. ⟨cea-01468372⟩ Plus de détails...
Experimental data from the Tore Supra experiments are extrapolated in the SOL and edge to investigate the Kelvin–Helmholtz instability. The linear analysis indicates that a large part of the SOL is rather unstable. The effort is part of the setup of the Mistral base case that is organised to validate the codes and address new issues on turbulent edges, including the comparison of kinetic and fluid modelling in the edge plasma.
Guilhem Dif-Pradalier, J Gunn, Guido Ciraolo, C S Chang, Guillaume Chiavassa, et al.. The Mistral base case to validate kinetic and fluid turbulence transport codes of the edge and SOL plasmas. Journal of Nuclear Materials, 2011, 415, ⟨10.1016/j.jnucmat.2010.12.035⟩. ⟨cea-01468372⟩
Coherent vorticity simulation (CVS) is a multiscale method to compute incompressible turbulent flows based on the wavelet filtered Navier-Stokes equations. At each time step the vorticity field is decomposed into two orthogonal components using an orthogonal wavelet basis: the coherent vorticity, corresponding to the coefficients whose modulus is larger than a threshold, and the remaining incoherent vorticity. The threshold value only depends on the total enstrophy, which evolves in time, and on the maximal resolution, which remains constant. The induced coherent velocity is computed from the coherent vorticity using the Biot-Savart kernel. To compute the flow evolution one only retains the coherent wavelet coefficients and some of their neighbors in space, scale, and direction, which define the safety zone. Two different strategies are studied to minimize at each time step the number of degrees of freedom to be computed, either by increasing the threshold value or by reducing the width of the safety zone. Their efficiency is compared for a three-dimensional forced homogeneous isotropic turbulent flow at initial Taylor microscale Reynolds number Rλ=153. The quality of the results is assessed in comparison to a direct numerical simulation of the same flow. It is found that, as long as a safety zone is present, CVS well preserves the statistical predictability of the turbulent flow (even the vorticity and velocity probability distribution functions) with a reduced number of degrees of freedom.
Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge, Yukio Kaneda. Coherent vorticity simulation of three-dimensional forced homogeneous isotropic turbulence. Multiscale Modeling and Simulation: A SIAM Interdisciplinary Journal, 2011, 9 (3), pp.1144-1161. ⟨10.1137/10079598X⟩. ⟨hal-01022690⟩
Journal: Multiscale Modeling and Simulation: A SIAM Interdisciplinary Journal
Benjamin Kadoch, K. Iyer, D. Donzis, Kai Schneider, Marie Farge, et al.. On the role of vortical structures for turbulent mixing using direct numerical simulation and wavelet-based coherent vorticity extraction. Journal of Turbulence, 2011, 12 (20), pp.1-17. ⟨10.1080/14685248.2011.562511⟩. ⟨hal-01022715⟩ Plus de détails...
The influence of vortical structures on the transport and mixing of passive scalars is investigated. Initial conditions are taken from a direct numerical simulation database of forced homogeneous isotropic turbulence, with passive scalar fluctuations, driven by a uniform mean gradient, are performed for Taylor microscale Reynolds numbers (R λ) of 140 and 240, and Schmidt numbers 1/8 and 1. For each R λ, after reaching a fully developed turbulent regime, which is statistically steady, the Coherent Vorticity Extraction is applied to the flow. It is shown that the coherent part is able to preserve the vortical structures with only less than 4% of wavelet coefficients while retaining 99.9% of energy. In contrast, the incoherent part is structureless and contains negligible energy. By taking the total, coherent and incoherent velocity fields in turn as initial conditions, new simulations were performed without forcing while the uniform mean scalar gradient is maintained. It is found that the results from simulations with total and coherent velocity fields as initial conditions are very similar. In contrast, the time integration of the incoherent flow exhibits its primarily dissipative nature. The evolutions of passive scalars at Schmidt numbers 1/8 and 1 advected by the total, coherent or incoherent velocity suggest that the vortical structures retained in the coherent part play a dominant role in turbulent transport and mixing. Indeed, the total and coherent flows give almost the same time evolution of the scalar variance, scalar flux and mean scalar dissipation, while the incoherent flow only gives rise to weak scalar diffusion.
Benjamin Kadoch, K. Iyer, D. Donzis, Kai Schneider, Marie Farge, et al.. On the role of vortical structures for turbulent mixing using direct numerical simulation and wavelet-based coherent vorticity extraction. Journal of Turbulence, 2011, 12 (20), pp.1-17. ⟨10.1080/14685248.2011.562511⟩. ⟨hal-01022715⟩
Nicolas Fedorczak, James Paul Gunn, Guido Ciraolo, Hugo Bufferand, Livia Isoardi, et al.. Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer. Journal of Nuclear Materials, 2011, 415 (1, Supplement 1), pp.S467-S470. ⟨10.1016/j.jnucmat.2010.10.034⟩. ⟨hal-01024052⟩ Plus de détails...
A consistent description of scrape-off layer transport is built from multi-diagnostic observations in ohmic discharges in Tore Supra. Fast imaging reveals the existence of relatively large filamentary structures on the low field side but not on the high field side of the torus. These filaments can exist either on open or closed magnetic flux surfaces and have a finite parallel extent from the outboard midplane. Probe electrostatic turbulence measured at the top of the plasma corresponds to the ExB convection of density burst, understood as the signature of filament propagation. Independent experiments on time-averaged parallel flows measured with a Mach probe lead to a poloidal mapping of the strongly asymmetric radial flux. This flux is centered at the outboard midplane and its poloidal half width is about 50°. The local turbulent flux on the top is consistent with the mapping.
Nicolas Fedorczak, James Paul Gunn, Guido Ciraolo, Hugo Bufferand, Livia Isoardi, et al.. Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer. Journal of Nuclear Materials, 2011, 415 (1, Supplement 1), pp.S467-S470. ⟨10.1016/j.jnucmat.2010.10.034⟩. ⟨hal-01024052⟩
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, 2011, 415 (1), pp.S613-S616. ⟨10.1016/j.jnucmat.2010.10.086⟩. ⟨hal-00848522⟩ Plus de détails...
Evidence of poloidally localized cross-field transport in experiments and theoretical analysis of turbulence transport governs the onset of parallel transport towards equilibrium. When cross-field transport appears in bursts, both for ELM relaxation events and microturbulence, the parallel transport of particles is shown to generate fronts that propagate with supersonic velocities. It is shown that after a short transient the density structure is no longer monotonic and that the two fronts (one co, the other counter the magnetic field) are independent. Furthermore, the time trace of the particle flux at a given location is characterized by a sharp rise followed by a longer time scale relaxation. Comparing the time delay and magnitude of the density burst at two locations allows to estimate the magnitude and the location of the generation of the front.
Guillaume Chiavassa, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih, Hervé Guillard, et al.. Parallel expansion of density bursts. Journal of Nuclear Materials, 2011, 415 (1), pp.S613-S616. ⟨10.1016/j.jnucmat.2010.10.086⟩. ⟨hal-00848522⟩
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. The Lighthill-Weis-Fogh clap-fling-sweep mechanism revisited. Journal of Fluid Mechanics, 2011, 676, pp.572-606. ⟨10.1017/jfm.2011.83⟩. ⟨hal-01022736⟩ Plus de détails...
The Lighthill-Weis-Fogh 'clap-fling-sweep' mechanism for lift generation in insect flight is re-examined. The novelty of this mechanism lies in the change of topology (the 'break') that occurs at a critical instant tc when two wings separate at their 'hinge' point as 'fling' gives way to 'sweep', and the appearance of equal and opposite circulations around the wings at this critical instant. Our primary aim is to elucidate the behaviour near the hinge point as time t passes through tc. First, Lighthill's inviscid potential flow theory is reconsidered. It is argued that provided the linear and angular accelerations of the wings are continuous, the velocity field varies continuously through the break, although the pressure field jumps instantaneously at t = tc. Then, effects of viscosity are considered. Near the hinge, the local Reynolds number is very small and local similarity solutions imply a logarithmic (integrable) singularity of the pressure jump across the hinge just before separation, in contrast to the 'negligible pressure jump' of inviscid theory invoked by Lighthill. We also present numerical simulations of the flow using a volume penalization technique to represent the motion of the wings. For Reynolds number equal to unity (based on wing chord), the results are in good agreement with the analytical solution. At a realistic Reynolds number of about 20, the flow near the hinge is influenced by leading-edge vortices, but local effects still persist. The lift coefficient is found to be much greater than that in the corresponding inviscid flow.
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. The Lighthill-Weis-Fogh clap-fling-sweep mechanism revisited. Journal of Fluid Mechanics, 2011, 676, pp.572-606. ⟨10.1017/jfm.2011.83⟩. ⟨hal-01022736⟩
Alfredo Pinelli, I. Z. Naqavi, Ugo Piomelli, Julien Favier. Immersed-boundary methods for general finite-difference and finite-volume Navier-Stokes solvers. Journal of Computational Physics, 2010, 229 (24), pp.9073-9091. ⟨10.1016/j.jcp.2010.08.021⟩. ⟨hal-00951516⟩ Plus de détails...
We present an immersed-boundary algorithm for incompressible flows with complex boundaries, suitable for Cartesian or curvilinear grid system. The key stages of any immersed-boundary technique are the interpolation of a velocity field given on a mesh onto a general boundary (a line in 2D, a surface in 3D), and the spreading of a force field from the immersed boundary to the neighboring mesh points, to enforce the desired boundary conditions on the immersed-boundary points. We propose a technique that uses the Reproducing Kernel Particle Method [W.K. Liu, S. Jun, Y.F. Zhang, Reproducing kernel particle methods, Int. J. Numer. Methods Fluids 20(8) (1995) 1081-1106] for the interpolation and spreading. Unlike other methods presented in the literature, the one proposed here has the property that the integrals of the force field and of its moment on the grid are conserved, independent of the grid topology (uniform or non-uniform, Cartesian or curvilinear). The technique is easy to implement, and is able to maintain the order of the original underlying spatial discretization. Applications to two- and three-dimensional flows in Cartesian and non-Cartesian grid system, with uniform and non-uniform meshes are presented.
Alfredo Pinelli, I. Z. Naqavi, Ugo Piomelli, Julien Favier. Immersed-boundary methods for general finite-difference and finite-volume Navier-Stokes solvers. Journal of Computational Physics, 2010, 229 (24), pp.9073-9091. ⟨10.1016/j.jcp.2010.08.021⟩. ⟨hal-00951516⟩
Matthieu J. Mercier, Denis Martinand, Manikandan Mathur, Louis Gostiaux, Thomas Peacock, et al.. New wave generation. Journal of Fluid Mechanics, 2010, 657, pp.308. ⟨10.1017/S0022112010002454⟩. ⟨hal-01139500⟩ Plus de détails...
We present the results of a combined experimental and numerical study of the generation of internal waves using the novel internal wave generator design of Gostiaux et al. (2007). This mechanism, which involves a tunable source comprised of oscillating plates, has so far been used for a few fundamental studies of internal waves, but its full potential has yet to be realized. Our studies reveal that this approach is capable of producing a wide variety of two-dimensional wave fields, including plane waves, wave beams and discrete vertical modes in finite-depth stratifications. The effects of discretization by a finite number of plates, forcing amplitude and angle of propagation are investigated, and it is found that the method is remarkably efficient at generating a complete wave field despite forcing only one velocity component in a controllable manner. We furthermore find that the nature of the radiated wave field is well predicted using Fourier transforms of the spatial structure of the wave generator.
Matthieu J. Mercier, Denis Martinand, Manikandan Mathur, Louis Gostiaux, Thomas Peacock, et al.. New wave generation. Journal of Fluid Mechanics, 2010, 657, pp.308. ⟨10.1017/S0022112010002454⟩. ⟨hal-01139500⟩
Jérôme Hoepffner, Alessandro Bottaro, Julien Favier. Mechanisms of non-modal energy amplification in channel flow between compliant walls. Journal of Fluid Mechanics, 2010, 642, pp.489-507. ⟨10.1017/S0022112009991935⟩. ⟨hal-01073478⟩ Plus de détails...
The mechanisms leading to large transient growth of disturbances for the flow in a channel with compliant walls are investigated. The walls are modeled as thin spring-backed plates, and the flow dynamics is modeled using the Navier-Stokes equations linearised round the Poiseuille profile. Analysis for streamwise-invariant perturbations show that this fluid- structure system can sustain oscillatory energy evolution of large amplitude, in the form of spanwise standing waves. Such waves are related to the travelling waves which a free wall can support, modified to account for an 'added mass' effect. Simple scaling arguments are found to provide results in excellent agreement with computations of optimal disturbances, for low to moderate values of the stiffness parameter characterising the compliant surface.
Jérôme Hoepffner, Alessandro Bottaro, Julien Favier. Mechanisms of non-modal energy amplification in channel flow between compliant walls. Journal of Fluid Mechanics, 2010, 642, pp.489-507. ⟨10.1017/S0022112009991935⟩. ⟨hal-01073478⟩
Ph. Druault, Ph Druault, M. Yu, P. Sagaut. Quadratic stochastic estimation of far-field acoustic pressure with coherent structure events in a 2D compressible plane mixing layer. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids, 2010, 62, pp.906 - 926. ⟨10.1002/fld.2047⟩. ⟨hal-02570155⟩ Plus de détails...
Mathematical tools based on cross correlations between aerodynamic quantities of interest inside the shear flow region and the radiated sound pressure are used to investigate noise generation mechanisms in a plane compressible mixing layer. An original methodology relying on an efficient coupling between proper orthogonal decomposition (POD) and stochastic estimation procedures is developed to analyze the main aerodynamic mechanisms that govern noise production. POD is used to split the instantaneous flow fluctuations as the sum of three components: the large-and small-scale coherent structures (LCS and SCS) and the background quasi-Gaussian fluctuations. Based on this flow partitioning, quadratic stochastic estimation is implemented to estimate the far-field acoustic pressure associated with each flow component. The far field acoustic pressure associated with both LCS and SCS is then investigated. By analyzing the RMS and temporal spectra of the far-field acoustic pressure, it is observed that the SCSs, as defined thanks to the POD basis, are responsible for the main part of the noise emission.
Ph. Druault, Ph Druault, M. Yu, P. Sagaut. Quadratic stochastic estimation of far-field acoustic pressure with coherent structure events in a 2D compressible plane mixing layer. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids, 2010, 62, pp.906 - 926. ⟨10.1002/fld.2047⟩. ⟨hal-02570155⟩
Journal: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids
Olivier Roussel, Kai Schneider. Coherent Vortex Simulation of weakly compressible turbulent mixing layers using adaptive multiresolution methods. Journal of Computational Physics, 2010, 229 (6), pp.2267-2286. ⟨10.1016/j.jcp.2009.11.034⟩. ⟨hal-01024617⟩ Plus de détails...
An adaptive mulitresolution method based on a second-order finite volume discretization is presented for solving the three-dimensional compressible Navier-Stokes equations in Cartesian geometry. The explicit time discretization is of second-order and for flux evaluation a 2-4 Mac Cormack scheme is used. Coherent Vortex Simulations (CVS) are performed by decomposing the flow variables into coherent and incoherent contributions. The coherent part is computed deterministically on a locally refined grid using the adaptive multiresolution method while the influence of the incoherent part is neglected to model turbulent dissipation. The computational efficiency of this approach in terms of memory and CPU time compression is illustrated for turbulent mixing layers in the weakly compressible regime and for Reynolds numbers based on the mixing layer thickness between 50 and 200. Comparisons with direct numerical simulations allow to assess the precision and efficiency of CVS.
Olivier Roussel, Kai Schneider. Coherent Vortex Simulation of weakly compressible turbulent mixing layers using adaptive multiresolution methods. Journal of Computational Physics, 2010, 229 (6), pp.2267-2286. ⟨10.1016/j.jcp.2009.11.034⟩. ⟨hal-01024617⟩
Raimund Burger, Ricardo Ruiz-Baier, Kai Schneider. Adaptive multiresolution methods for the simulation of waves in excitable media. Journal of Scientific Computing, 2010, 43 (2), pp.261-290. ⟨10.1007/s10915-010-9356-3⟩. ⟨hal-01024084⟩ Plus de détails...
We present fully adaptive multiresolution methods for a class of spatially two-dimensional reaction-diffusion systems which describe excitable media and often give rise to the formation of spiral waves. A novel model ingredient is a strongly degenerate diffusion term that controls the degree of spatial coherence and serves as a mechanism for obtaining sharper wave fronts. The multiresolution method is formulated on the basis of two alternative reference schemes, namely a classical finite volume method, and Barkley's approach (Barkley in Phys. D 49:61-70, 1991), which consists in separating the computation of the nonlinear reaction terms from that of the piecewise linear diffusion. The proposed methods are enhanced with local time stepping to attain local adaptivity both in space and time. The computational efficiency and the numerical precision of our methods are assessed. Results illustrate that the fully adaptive methods provide stable approximations and substantial savings in memory storage and CPU time while preserving the accuracy of the discretizations on the corresponding finest uniform grid.
Raimund Burger, Ricardo Ruiz-Baier, Kai Schneider. Adaptive multiresolution methods for the simulation of waves in excitable media. Journal of Scientific Computing, 2010, 43 (2), pp.261-290. ⟨10.1007/s10915-010-9356-3⟩. ⟨hal-01024084⟩
Kai Schneider, Oleg V. Vasilyev. Wavelet methods in computational fluid dynamics. Annual Review of Fluid Mechanics, 2010, 42, pp.473-503. ⟨10.1146/annurev-fluid-121108-145637⟩. ⟨hal-01024632⟩ Plus de détails...
This article reviews state-of-the-art adaptive, multiresolution wavelet methodologies for modeling and simulation of turbulent flows with various examples. Different numerical methods for solving the Navier-Stokes equations in adaptive wavelet bases are described. We summarize coherent vortex extraction methodologies, which utilize the efficient wavelet decomposition of turbulent flows into space-scale contributions, and present a hierarchy of wavelet-based turbulence models. Perspectives for modeling and computing industrially relevant flows are also given.
Kai Schneider, Oleg V. Vasilyev. Wavelet methods in computational fluid dynamics. Annual Review of Fluid Mechanics, 2010, 42, pp.473-503. ⟨10.1146/annurev-fluid-121108-145637⟩. ⟨hal-01024632⟩
Dmitry Kolomenskiy, Kai Schneider. Numerical simulations of falling leaves using a pseudo-spectral method with volume penalization. Theoretical and Computational Fluid Dynamics, 2010, 24 (1-4), pp.169-173. ⟨10.1007/s00162-009-0171-0⟩. ⟨hal-01024134⟩ Plus de détails...
The dynamics of falling leaves is studied by means of numerical simulations. The two-dimensional incompressible Navier-Stokes equations, coupled with the equations governing solid body dynamics, are solved using a Fourier pseudo-spectral method with volume penalization to impose no-slip boundary conditions. Comparison with other numerical methods is made. Simulations performed for different values of the Reynolds number show that its decrease stabilizes the free fall motion.
Dmitry Kolomenskiy, Kai Schneider. Numerical simulations of falling leaves using a pseudo-spectral method with volume penalization. Theoretical and Computational Fluid Dynamics, 2010, 24 (1-4), pp.169-173. ⟨10.1007/s00162-009-0171-0⟩. ⟨hal-01024134⟩
Journal: Theoretical and Computational Fluid Dynamics
Brian Launder, Sébastien Poncet, Eric Serre. Laminar, transitional, and turbulent flows in rotor-stator cavities. Annual Review of Fluid Mechanics, 2010, 42 (1), pp.229-248. ⟨10.1146/annurev-fluid-121108-145514⟩. ⟨hal-00678846⟩ Plus de détails...
This article reviews the range of flows that may be created within thin cylindrical or annular cavities due to the rotation of one of the confining disks. At low Reynolds numbers, the rotation gives rise to an axisymmetric, radially outward motion near the rotor with a return flow along the stationary disk. As the Reynolds number is raised, this base flow gives way to a shear flow populated by discrete vortices, whether of cylindrical or spiral form, near both the rotating and stationary disks. At Reynolds numbers high enough for turbulent flow to occur, in the twentieth century both experimental and computational studies treated the flow as axisymmetric and steady. Recent research has shown, however, that complex organized structures also persist in the turbulent regime.
Brian Launder, Sébastien Poncet, Eric Serre. Laminar, transitional, and turbulent flows in rotor-stator cavities. Annual Review of Fluid Mechanics, 2010, 42 (1), pp.229-248. ⟨10.1146/annurev-fluid-121108-145514⟩. ⟨hal-00678846⟩
Benjamin Kadoch, Emmanuel Leriche, Kai Schneider, Marie Farge. On the Role of Coherent Structures in a Lid Driven Cavity Flow. Turbulence and Interactions., pp.207-214, 2010, ⟨10.1007/978-3-642-14139-3_25⟩. ⟨hal-02535124⟩ Plus de détails...
Benjamin Kadoch, Emmanuel Leriche, Kai Schneider, Marie Farge. On the Role of Coherent Structures in a Lid Driven Cavity Flow. Turbulence and Interactions., pp.207-214, 2010, ⟨10.1007/978-3-642-14139-3_25⟩. ⟨hal-02535124⟩
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Pressure-driven radial flow in a Taylor-Couette cell. Journal of Fluid Mechanics, 2010, 660, pp.527-537. ⟨10.1017/S0022112010003228⟩. ⟨hal-01024690⟩ Plus de détails...
A generalized solution for pressure-driven flow through a permeable rotating inner cylinder in an impermeable concentric outer cylinder, a situation used commercially in rotating filtration, is challenging due to the interdependence between the pressure drop in the axial direction and that across the permeable inner cylinder. Most previous approaches required either an imposed radial velocity at the inner cylinder or radial throughflow with both the inner and outer cylinders being permeable. We provide an analytical solution for rotating Couette-Poiseuille flow with Darcy's law at the inner cylinder by using a small parameter related to the permeability of the inner cylinder. The theory works for suction, injection and even combined suction/injection, when the axial pressure drop in the annulus is such that the transmembrane pressure difference reverses sign along the axial extent of the system. Corresponding numerical simulations for finite-length systems match the theory very well.
Nils Tilton, Denis Martinand, Eric Serre, Richard M. Lueptow. Pressure-driven radial flow in a Taylor-Couette cell. Journal of Fluid Mechanics, 2010, 660, pp.527-537. ⟨10.1017/S0022112010003228⟩. ⟨hal-01024690⟩
Romain Nguyen van Yen, Diego Del-Castillo-Negrete, Kai Schneider, Marie Farge, Guangye Chen. Wavelet-based density estimation for noise reduction in plasma simulations using particles. Journal of Computational Physics, 2010, 229 (8), pp.2821-2839. ⟨10.1016/j.jcp.2009.12.010⟩. ⟨hal-00828015⟩ Plus de détails...
For given computational resources, the accuracy of plasma simulations using particles is mainly held back by the noise due to limited statistical sampling in the reconstruction of the particle distribution function. A method based on wavelet analysis is proposed and tested to reduce this noise. The method, known as wavelet based density estimation (WBDE), was previously introduced in the statistical literature to estimate probability densities given a finite number of independent measurements. Its novel application to plasma simulations can be viewed as a natural extension of the finite size particles (FSP) approach, with the advantage of estimating more accurately distribution functions that have localized sharp features. The proposed method preserves the moments of the particle distribution function to a good level of accuracy, has no constraints on the dimensionality of the system, does not require an a priori selection of a global smoothing scale, and its able to adapt locally to the smoothness of the density based on the given discrete particle data. Most importantly, the computational cost of the denoising stage is of the same order as one time step of a FSP simulation. The method is compared with a recently proposed proper orthogonal decomposition based method, and it is tested with three particle data sets that involve different levels of collisionality and interaction with external and self-consistent fields.
Romain Nguyen van Yen, Diego Del-Castillo-Negrete, Kai Schneider, Marie Farge, Guangye Chen. Wavelet-based density estimation for noise reduction in plasma simulations using particles. Journal of Computational Physics, 2010, 229 (8), pp.2821-2839. ⟨10.1016/j.jcp.2009.12.010⟩. ⟨hal-00828015⟩
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. Vorticity generation during the clap-fling-sweep of some hovering insects. Theoretical and Computational Fluid Dynamics, 2010, 24 (1-4), pp.209-215. ⟨10.1007/s00162-009-0137-2⟩. ⟨hal-01024119⟩ Plus de détails...
Numerical simulations of the Lighthill-Weis-Fogh mechanism are performed using a Fourier pseudo-spectral method with volume penalization. Single-winged and double-winged configurations are compared, and the vortex shedding patterns are related to the lift generated in both cases. The computations of the lift coefficient are validated against the results reported previously by Miller and Peskin (J Exp Biol 208:195-212, 2005).
Dmitry Kolomenskiy, H.K. Moffatt, Marie Farge, Kai Schneider. Vorticity generation during the clap-fling-sweep of some hovering insects. Theoretical and Computational Fluid Dynamics, 2010, 24 (1-4), pp.209-215. ⟨10.1007/s00162-009-0137-2⟩. ⟨hal-01024119⟩
Journal: Theoretical and Computational Fluid Dynamics
K. Schneider, S. Neffaa, Benjamin Kadoch, W. Bos. Lagrangian intermittency and time-correlations in two-dimensional turbulence. dvances in Turbulence XII, pp.737-740, 2009, ⟨10.1007/978-3-642-03085-7_179⟩. ⟨hal-02535186⟩ Plus de détails...
K. Schneider, S. Neffaa, Benjamin Kadoch, W. Bos. Lagrangian intermittency and time-correlations in two-dimensional turbulence. dvances in Turbulence XII, pp.737-740, 2009, ⟨10.1007/978-3-642-03085-7_179⟩. ⟨hal-02535186⟩
D. Kolomensky, Benjamin Kadoch, W. Bos, K. Schneider, P. Angot. Scalar mixing in turbulent confined flow. Advances in Turbulence XII, pp.525-528, 2009, ⟨10.1007/978-3-642-03085-7_126⟩. ⟨hal-02535201⟩ Plus de détails...
D. Kolomensky, Benjamin Kadoch, W. Bos, K. Schneider, P. Angot. Scalar mixing in turbulent confined flow. Advances in Turbulence XII, pp.525-528, 2009, ⟨10.1007/978-3-642-03085-7_126⟩. ⟨hal-02535201⟩
Benjamin Kadoch, W. Bos, K. Schneider. Lagrangian statistics of two–dimensional turbulence in a square container. Advances in Turbulence XII, pp.35-38, 2009, ⟨10.1007/978-3-642-03085-7_8⟩. ⟨hal-02535140⟩ Plus de détails...
Benjamin Kadoch, W. Bos, K. Schneider. Lagrangian statistics of two–dimensional turbulence in a square container. Advances in Turbulence XII, pp.35-38, 2009, ⟨10.1007/978-3-642-03085-7_8⟩. ⟨hal-02535140⟩
Alessandro Bottaro, Julien Favier, Joel Guerrero, Divya Venkataraman, Hakan Wedin. Sulla scia di Icaro. Sapere, Edizioni Dedalo, pp.66-77, 2009, 9788822093981. ⟨hal-01073987⟩ Plus de détails...
La progettazione di velivoli dal minimo attrito tiene impegnati i ricercatori del DICAT di Genova che lavorano al progetto europeo FLUBIO. La realizzazione del "perfetto automa volante" trae ispirazione dalla natura e in particolare dal volo dell'airone, un ottimo modello per velivoli con ali ricoperte da piume che battono al vento
Alessandro Bottaro, Julien Favier, Joel Guerrero, Divya Venkataraman, Hakan Wedin. Sulla scia di Icaro. Sapere, Edizioni Dedalo, pp.66-77, 2009, 9788822093981. ⟨hal-01073987⟩
Benjamin Kadoch, Margarete Oliveira Domingues, Ingmar Broemstrup, Lionel Larchevêque, Kai Schneider, et al.. Coherent Vorticity Extraction in 3D Homogeneous Isotropic Turbulence: Influence of the Reynolds Number and Geometrical Statistics. Brazilian Journal of Physics, 2009, 39. ⟨hal-02081129⟩ Plus de détails...
The coherent vorticity extraction method (CVE) is based on the nonlinear filtering of the vorticity field projected onto an orthonormal wavelet basis made of compactly supported functions. CVE decomposes each turbulent flow realization into two orthogonal components: a coherent and an incoherent random flow. They both contribute to all scales in the inertial range, but exhibit different statistical behavior. We apply CVE to 256 3 subcubes extracted from 3D homogeneous isotropic turbulent flows at different Taylor microscale Reynolds numbers (R λ = 140, 240 and 680), computed by a direct numerical simulation (DNS) at different resolutions (N = 256 3 , 512 3 and 2048 3), respectively. We compare the total, coherent and incoherent vorticity fields obtained by using CVE and show that few wavelets coefficients are sufficient to represent the coherent vortices of the flows. Geometrical statistics in term of helicity are also analyzed and the λ 2 criterion is applied to the filtered flow fields.
Benjamin Kadoch, Margarete Oliveira Domingues, Ingmar Broemstrup, Lionel Larchevêque, Kai Schneider, et al.. Coherent Vorticity Extraction in 3D Homogeneous Isotropic Turbulence: Influence of the Reynolds Number and Geometrical Statistics. Brazilian Journal of Physics, 2009, 39. ⟨hal-02081129⟩
Laurent Cordier, Badr Abou El Majd, Julien Favier. Calibration of POD reduced-order models using Tikhonov regularization. International Journal for Numerical Methods in Fluids, 2009, 63 (2), pp.269-296. ⟨10.1002/fld.2074⟩. ⟨hal-01073978⟩ Plus de détails...
In this paper we compare various methods of calibration that can be used in practice to improve the accuracy of reduced-order models based on Proper Orthogonal Decomposition. The bench mark configuration retained corresponds to a case of relatively simple dynamics: a two-dimensional flow around a cylinder for a Reynolds number of 200. We generalize to the first and second-order the method of calibration based on Tikhonov regularization recently used in [1]. Finally, we show that for this flow configuration this procedure is the most effective in terms of reduction of errors.
Laurent Cordier, Badr Abou El Majd, Julien Favier. Calibration of POD reduced-order models using Tikhonov regularization. International Journal for Numerical Methods in Fluids, 2009, 63 (2), pp.269-296. ⟨10.1002/fld.2074⟩. ⟨hal-01073978⟩
Journal: International Journal for Numerical Methods in Fluids
Julien Favier, Antoine Dauptain, Davide Basso, Alessandro Bottaro. Passive separation control using a self-adaptive hairy coating. Journal of Fluid Mechanics, 2009, 627, pp.451 - 483. ⟨hal-01073967⟩ Plus de détails...
A model of hairy medium is developed using a homogenized approach, and the fluid flow around a circular cylinder partially coated with hair is analyzed by means of nu- merical simulations. The capability of this coating to adapt to the surrounding flow is investigated, and its benefits are discussed in the context of separation control. This fluid-structure interaction problem is solved with a partitioned approach, based on the direct resolution of the Navier-Stokes equations together with a non-linear set of equa- tions describing the dynamics of the coating. A volume force, arising from the presence of a cluster of hair, provides the link between the fluid and the structure problems. For the structure part, a subset of reference elements approximates the whole layer. The dy- namics of these elements is governed by a set of equations based on the inertia, elasticity, interaction and losses effects of articulated rods. The configuration chosen is that of the two-dimensional flow past a circular cylinder at Re = 200, a simple and well documented test case. Aerodynamics performances quantified by the Strouhal number, the drag and the maximum lift in the laminar unsteady regime are modified by the presence of the coating. A set of parameters corresponding to a realistic coating (length of elements, porosity, rigidity) is found, yielding an average drag reduction of 15% and a decrease of lift fluctuations by about 40%, associated to a stabilization of the wake.
Julien Favier, Antoine Dauptain, Davide Basso, Alessandro Bottaro. Passive separation control using a self-adaptive hairy coating. Journal of Fluid Mechanics, 2009, 627, pp.451 - 483. ⟨hal-01073967⟩
Henning Bockhorn, Jordan Denev, Margarete Domingues, Carlos Falconi, Marie Farge, et al.. Numerical Simulation of Turbulent Flows in Complex Geometries Using the Coherent Vortex Simulation Approach Based on Orthonormal Wavelet Decomposition. Numerical Simulation of Turbulent Flows and Noise Generation, pp.175-200, 2009, ⟨10.1007/978-3-540-89956-3_8⟩. ⟨hal-02535064⟩ Plus de détails...
Henning Bockhorn, Jordan Denev, Margarete Domingues, Carlos Falconi, Marie Farge, et al.. Numerical Simulation of Turbulent Flows in Complex Geometries Using the Coherent Vortex Simulation Approach Based on Orthonormal Wavelet Decomposition. Numerical Simulation of Turbulent Flows and Noise Generation, pp.175-200, 2009, ⟨10.1007/978-3-540-89956-3_8⟩. ⟨hal-02535064⟩
Livia Isoardi, Guido Ciraolo, Guillaume Chiavassa, Pierre Haldenwang, Eric Serre, et al.. Modelling SOL flow pattern spreading in the edge plasma. Journal of Nuclear Materials, 2009, 390-391, pp.388-391. ⟨10.1016/j.jnucmat.2009.01.088⟩. ⟨hal-00848559⟩ Plus de détails...
The transition region between closed and open magnetic flux surfaces plays a crucial role for tokamak performances. Appropriate understanding of the edge region remains a major challenge owing to several open issues as momentum transport, turbulence overshoot or neutral penetration. We consider here a transport model system to investigate the propagation of parallel momentum from the SOL into the core plasma and vice-versa. The numerical results show that for small values of the radial diffusion coefficient, the density profile decays exponentially from the core to the SOL as predicted by 1D analytical solution. A spreading of the parallel momentum from the SOL to the core is observed, with the presence of non-zero velocities also in the regions far from the SOL. The effect of an imposed rotation of the core plasma is investigated as well as the dynamics of an overdensity imposed in the core plasma.
Livia Isoardi, Guido Ciraolo, Guillaume Chiavassa, Pierre Haldenwang, Eric Serre, et al.. Modelling SOL flow pattern spreading in the edge plasma. Journal of Nuclear Materials, 2009, 390-391, pp.388-391. ⟨10.1016/j.jnucmat.2009.01.088⟩. ⟨hal-00848559⟩
Antoine Dauptain, Julien Favier, Alessandro Bottaro. Hydrodynamics of ciliary propulsion. Journal of Fluids and Structures, 2008, 24 (8), pp.1156-1165. ⟨10.1016/j.jfluidstructs.2008.06.007⟩. ⟨hal-01073968⟩ Plus de détails...
A numerical approach is developed to study the effect on a fluid of the regular oscillations of an array of flexible cilia which hinge around points on a wall. The specific application studied concerns the ctenophore Pleurobrachia pileus, a small marine invertebrate of quasi-spherical shape and diameter of the order of the centimeter which swims in water thanks to the rhythmic beating of eight rows of hair-like cilia aligned along its body. Only one row of cilia is studied here, in a three-dimensional setting. The technique presented is general enough to allow its application to a variety of fluid-structure interaction problems. The physical mechanisms of the propulsion are highlighted, by analysing the results of three-dimensional simulations. A parametric study involving natural and non-natural parameters leads to a better understanding of the propulsive characteristics of ctenophores; results show that the specific power expended increases with the increase of the beating frequency of the row of cilia, in agreement with experiments.
Antoine Dauptain, Julien Favier, Alessandro Bottaro. Hydrodynamics of ciliary propulsion. Journal of Fluids and Structures, 2008, 24 (8), pp.1156-1165. ⟨10.1016/j.jfluidstructs.2008.06.007⟩. ⟨hal-01073968⟩
Emilia Crespo del Arco, José Sanchez Alvarez, Eric Serre, A. de La Torre, Javier Burguete. Numerical and experimental study of the time dependent states and the slow dynamics in a von Karman swirling flow. Geophysical and Astrophysical Fluid Dynamics, 2008, 103 (2), pp.1-15. ⟨hal-01023287⟩ Plus de détails...
Emilia Crespo del Arco, José Sanchez Alvarez, Eric Serre, A. de La Torre, Javier Burguete. Numerical and experimental study of the time dependent states and the slow dynamics in a von Karman swirling flow. Geophysical and Astrophysical Fluid Dynamics, 2008, 103 (2), pp.1-15. ⟨hal-01023287⟩
Journal: Geophysical and Astrophysical Fluid Dynamics
Bertrand Viaud, Eric Serre, Jean-Marc Chomaz. Elephant mode sitting on a rotating disk in an annulus. Journal of Fluid Mechanics, 2008, 598, pp.451-464. ⟨hal-01023281⟩ Plus de détails...
Bertrand Viaud, Eric Serre, Jean-Marc Chomaz. Elephant mode sitting on a rotating disk in an annulus. Journal of Fluid Mechanics, 2008, 598, pp.451-464. ⟨hal-01023281⟩
Eric Serre, Mathieu Minguez, Richard Pasquetti. Spectral vanishing viscosity stabilized LES of the Ahmed body turbulent wake. Communications in Computational Physics, 2008, 5 (2-4), pp.635-648. ⟨hal-01023286⟩ Plus de détails...
Eric Serre, Mathieu Minguez, Richard Pasquetti. Spectral vanishing viscosity stabilized LES of the Ahmed body turbulent wake. Communications in Computational Physics, 2008, 5 (2-4), pp.635-648. ⟨hal-01023286⟩
Eric Serre, Michael Sprague, Richard M. Lueptow. Stability of Taylor-Couette flow with radial throughflow. Physics of Fluids, 2008, 20 (3), pp.034106. ⟨hal-01023284⟩ Plus de détails...
Eric Serre, Michael Sprague, Richard M. Lueptow. Stability of Taylor-Couette flow with radial throughflow. Physics of Fluids, 2008, 20 (3), pp.034106. ⟨hal-01023284⟩
B. Viaud, E. Serre, Jean-Marc Chomaz. The elephant mode between two rotating disks. Journal of Fluid Mechanics, 2008, 598 (mars), pp.451-464. ⟨10.1017/s0022112007009962⟩. ⟨hal-01022811⟩ Plus de détails...
B. Viaud, E. Serre, Jean-Marc Chomaz. The elephant mode between two rotating disks. Journal of Fluid Mechanics, 2008, 598 (mars), pp.451-464. ⟨10.1017/s0022112007009962⟩. ⟨hal-01022811⟩
Richard Pasquetti, Eric Séverac, Eric Serre, Patrick Bontoux, Michael Schaefer. From stratified wake to rotor-stator flows by a SVV-LES method. Theoretical and Computational Fluid Dynamics, 2008, 22 (3-4), pp.261-273. ⟨hal-01023280⟩ Plus de détails...
Richard Pasquetti, Eric Séverac, Eric Serre, Patrick Bontoux, Michael Schaefer. From stratified wake to rotor-stator flows by a SVV-LES method. Theoretical and Computational Fluid Dynamics, 2008, 22 (3-4), pp.261-273. ⟨hal-01023280⟩
Journal: Theoretical and Computational Fluid Dynamics
Margarete Domingues, Ingmar Broemstrup, Kai Schneider, Marie Farge, Benjamin Kadoch. Coherent vortex extraction in 3D homogeneous isotropic turbulence using orthogonal wavelets. ESAIM: Proceedings, 2007, CEMRACS 2005 - Computational Aeroacoustics and Computational Fluid Dynamics in Turbulent Flows, 16, pp.164-180. ⟨10.1051/proc:2007005⟩. ⟨hal-02535148⟩ Plus de détails...
The coherent vortex extraction (CVE) decomposes each turbulent flow realization into two orthogonal components: a coherent and a random incoherent flow. They both contribute to all scales in the inertial range, but exhibit different statistical behaviour. The CVE decomposition is based on the nonlinear filtering of the vorticity field projected onto an orthonormal wavelet basis made of compactly supported functions. We decompose a 3D homogeneous isotropic turbulent flow at Taylor microscale Reynolds numbers R$_λ$ = 140 computed by a direct numerical simulation (DNS) at resolution N = 256$^3$. Only wavelet modes correspond to the coherent flow made of vortex tubes, which contributes to of the enstrophy. Another observation is that the coherent flow exhibits in the inertial range the same $k^{-5/3}$ slope in the energy spectrum and slope in the enstrophy spectrum as the total flow does. The remaining 96.3 %N wavelet modes correspond to a random residual flow which is structureless, quasi equipartition of energy and a Gaussian velocity probability distribution function (PDF). We also analyse and visualize the Lamb vector, its divergence and curl and study the contributions coming from the coherent and incoherent components of vorticity and the induced velocity.
Margarete Domingues, Ingmar Broemstrup, Kai Schneider, Marie Farge, Benjamin Kadoch. Coherent vortex extraction in 3D homogeneous isotropic turbulence using orthogonal wavelets. ESAIM: Proceedings, 2007, CEMRACS 2005 - Computational Aeroacoustics and Computational Fluid Dynamics in Turbulent Flows, 16, pp.164-180. ⟨10.1051/proc:2007005⟩. ⟨hal-02535148⟩
Julien Favier, Laurent Cordier, Azeddine Kourta. Sur l’optimisation d’actionneurs pour le contrôle d’écoulements. Mechanics & Industry, 2007, 8, pp.259-265. ⟨10.1051/meca:2007047⟩. ⟨hal-01073972⟩ Plus de détails...
L'objectif de ce travail est de construire par POD (@ Proper Orthogonal Decomposition A) des mod'eles d'ordre r ́eduit permettant de reproduire de mani'ere fiable la dynamique spatio-temporelle d'un ́ecoulement d ́ecoll ́e. L'int ́erˆet croissant pour ces mod'eles r ́eduits de dynamique s'explique par leur utilisation potentielle dans la r ́esolution de probl'emes d'optimisation sous contraintes de grande taille, rencontr ́es en controˆle d' ́ecoulements. La d ́emarche g ́en ́erale consiste 'a remplacer le mod'ele d ́etaill ́e de l' ́ecoulement (les ́equations de Navier-Stokes), par un mod'ele approch ́e, plus rapide 'a r ́esoudre et contenant les caract ́eristiques essentielles de la dynamique. La POD, optimale au sens de la reconstruction ́energ ́etique, permet d'approximer la dynamique de l' ́ecoulement dans un sous-espace g ́en ́er ́e par un petit nombre de modes. Diff ́erentes m ́ethodes de calibration sont ici d ́evelopp ́ees afin d'am ́eliorer la pr ́ediction du mod'ele de dimension r ́eduite, et ainsi rendre cette approche utilisable dans le cadre d'une probl ́ematique de contrˆole d' ́ecoulements. Essentiellement, ces m ́ethodes consistent 'a ajouter aux ́equations du mod'ele des termes suppl ́ementaires calcul ́es comme solutions d'un probl'eme de minimisation sous contraintes.
Julien Favier, Laurent Cordier, Azeddine Kourta. Sur l’optimisation d’actionneurs pour le contrôle d’écoulements. Mechanics & Industry, 2007, 8, pp.259-265. ⟨10.1051/meca:2007047⟩. ⟨hal-01073972⟩
Julien Favier, Azeddine Kourta. Étude du contrôle du décollement sur un profil d'aile par mesures PIV et analyse POD. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2006, 334, pp.272-278. ⟨10.1016/j.crme.2006.02.005⟩. ⟨hal-01073970⟩ Plus de détails...
The purpose of this study is the active control of flow separation on an ONERA D airfoil, using continuous blowing microjets. Particle Image Velocimetry (PIV) is used to measure velocity fields at midspan around the airfoil in both controlled and uncontrolled cases. Post-processing based on Proper Orthogonal Decomposition (POD) is developed to exhibit the main energetic features of the flow. Therefore, the detailed study of the POD modes for separated and stalled cases leads to a better understanding of the control mechanisms. Moreover, the POD basis computed for uncontrolled and controlled cases, opens the way to optimisation of control strategies.
Julien Favier, Azeddine Kourta. Étude du contrôle du décollement sur un profil d'aile par mesures PIV et analyse POD. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2006, 334, pp.272-278. ⟨10.1016/j.crme.2006.02.005⟩. ⟨hal-01073970⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Pierre Magnico, P. Fongarland. CFD simulations of two stirred tank reactors with stationary catalytic basket. Chemical Engineering Science, 2006, 61 (4), pp.1217-1236. ⟨10.1016/j.ces.2005.07.025⟩. ⟨hal-01089397⟩ Plus de détails...
Among the different systems used for laboratory kinetic investigation, stationary catalytic basket stirred tank reactors (SCBSTRs) allow one to study triphasic reactions involving shaped catalyst with large size. The hydrodynamics of these complex reactors is not well known and has been studied experimentally in only a few cases. Despite the difference in the design of two commercial SCBSTRs reported in these works, the local measurements of the liquid–solid mass transfer coefficient inside the catalytic basket revealed the same velocity profile. The aim of the present work is therefore to investigate more accurately the hydrodynamics of the two reactors by means of CFD in order to compare the effect of the blade/baffle hydrodynamic interaction on the flow pattern. Owing to the geometrical complexity of the reactors, the hydrodynamic investigation is based on the kk–εε model and the Brinkman–Forsheimer equations. The agreement at the local level with the experimental data (PIV and mass transfer measurements) validates this preliminary work performed with the standard values of the parameters present in the turbulent model and the Brinkman–Forsheimer equations. The simulations reveal in both reactors a ring-shaped vortex around the impeller in the agitation region. The high axial location of its centre induces a reverse flow at the tips of the basket. Owing to the fluid friction in the porous medium, the azimuthal flow in the core region is transformed into a radial flow in the basket where the flow decreases abruptly. Vertical vortices are located at the blade tips and at the downstream face of the baffles or they are located in the basket on both sides of the baffles, depending on the design and the location of the baffles. At the inner radius interface of the basket, the vertical blade impeller induces a rather homogeneous velocity profile, but the pitched blade impeller imposes a high velocity at the plane of symmetry. Therefore the simulations demonstrate that two different local velocity patterns and two different porous media may induce the same mass transfer properties.
Pierre Magnico, P. Fongarland. CFD simulations of two stirred tank reactors with stationary catalytic basket. Chemical Engineering Science, 2006, 61 (4), pp.1217-1236. ⟨10.1016/j.ces.2005.07.025⟩. ⟨hal-01089397⟩
Sébastien Bourgois, Jean Tensi, Emmanuel Sommier, Julien Favier. Experimental Investigations on Fluidic Control Over an Airfoil. Journal of Flow Visualization and Image Processing, 2006, 13 (3), pp.265-286. ⟨10.1615/JFlowVisImageProc.v13.i3.40⟩. ⟨hal-01073973⟩ Plus de détails...
This study presents the development of two fluidic actuators − namely, microjets and tangential blowing actuator (TBA), designed for flow separation control. The developed actuators are compact enough to fit inside an ONERA D profiled wing with a chord of 0.35 m. Test bench experiments showed that the microjets (resp. TBA) were able to produce exit velocities up to 330 m/s (resp. 60 m/s). These actuators were placed in the model and were tested in wind tunnels for various blowing rates. The investigations included the use of force balance measurements, on-surface flow visualization with pigmented oil, off-surface flow visualizations with smoke, surface pressure distribution measurements, and Particle Image Velocimetry (PIV). Most of the tests were performed at free-stream velocities between 20 m/s (for PIV) and 40 m/s, corresponding to Reynolds numbers in the range 0.47 × 10^6−0.93 × 10^6 . The angle of attack varied from −2 to 20 degrees. Experiments were conducted using the naturally occurring laminar boundary layer as well as for a turbulent boundary layer. In such a case, rough strips were used in the vicinity of the leading edge. The present tests show the efficiency of these devices to delay separation and improve aerodynamic performances of the wing: for example, a maximum of 30% gain in CL has been reached using the microjets. Both actuators tend to increase the lift coefficient CL after stall and areas of separated flow have been eliminated by applying control, as suggested by flow visualizations and PIV velocity fields.
Sébastien Bourgois, Jean Tensi, Emmanuel Sommier, Julien Favier. Experimental Investigations on Fluidic Control Over an Airfoil. Journal of Flow Visualization and Image Processing, 2006, 13 (3), pp.265-286. ⟨10.1615/JFlowVisImageProc.v13.i3.40⟩. ⟨hal-01073973⟩
Journal: Journal of Flow Visualization and Image Processing
K. Schneider, M. Farge. Numerical simulation of the transient flow behaviour in tube bundles using a volume penalization method. Journal of Fluids and Structures, 2005, 20 (4), pp.555-566. ⟨10.1016/j.jfluidstructs.2005.02.006⟩. ⟨hal-01299228⟩ Plus de détails...
We present high resolution numerical simulations of incompressible two-dimensional flows in tube bundles, staggered or in-line, as encountered in heat exchangers or chemical reactors. We study the time evolution of several flows in arrays of cylinders, squares and double-cruciform shaped tubes at a Reynolds number of 200. The numerical scheme is either based on adaptive wavelet or Fourier pseudo-spectral space discretization with adaptive time stepping. A volume penalization method is used to impose no-slip boundary conditions on the tubes. Lift and drag coefficients for the different geometries of tube bundles are compared and perspectives for fluid–structure interaction are given.
K. Schneider, M. Farge. Numerical simulation of the transient flow behaviour in tube bundles using a volume penalization method. Journal of Fluids and Structures, 2005, 20 (4), pp.555-566. ⟨10.1016/j.jfluidstructs.2005.02.006⟩. ⟨hal-01299228⟩
Clemente Rodriguez, Eric Serre, Claude Rey. A numerical model for shallow-water flows: dynamics of the eddy shedding. WSEAS Transactions on Environment and Development, 2005, 1 (2), pp.280-287. ⟨hal-01023278⟩ Plus de détails...
Clemente Rodriguez, Eric Serre, Claude Rey. A numerical model for shallow-water flows: dynamics of the eddy shedding. WSEAS Transactions on Environment and Development, 2005, 1 (2), pp.280-287. ⟨hal-01023278⟩
Journal: WSEAS Transactions on Environment and Development
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich H. Busse. Square patterns in rotating Rayleigh-Bénard convection. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2005, 72, pp.036307. ⟨hal-01023277⟩ Plus de détails...
José Sanchez Alvarez, Eric Serre, Emilia Crespo del Arco, Friedrich H. Busse. Square patterns in rotating Rayleigh-Bénard convection. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2005, 72, pp.036307. ⟨hal-01023277⟩
Journal: Physical Review E : Statistical, Nonlinear, and Soft Matter Physics
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Ekman vortices and the centrifugal instability in the counter-rotating cylindrical Couette flow. Theoretical and Computational Fluid Dynamics, 2004, 18 (2-4), pp.151-168. ⟨hal-01023276⟩ Plus de détails...
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Ekman vortices and the centrifugal instability in the counter-rotating cylindrical Couette flow. Theoretical and Computational Fluid Dynamics, 2004, 18 (2-4), pp.151-168. ⟨hal-01023276⟩
Journal: Theoretical and Computational Fluid Dynamics
Eric Serre, Ewa Tuliszka-Sznitko, Patrick Bontoux. Coupled theoretical and numerical study of the flow transition between a rotating and a stationary disk. Physics of Fluids, 2004, 16 (3), pp.688-706. ⟨hal-01023275⟩ Plus de détails...
Eric Serre, Ewa Tuliszka-Sznitko, Patrick Bontoux. Coupled theoretical and numerical study of the flow transition between a rotating and a stationary disk. Physics of Fluids, 2004, 16 (3), pp.688-706. ⟨hal-01023275⟩
Eric Serre, Peter K. Stansby, Dominique R. Laurence, Brian Launder. Ecoulement autour d'un modèle d'île conique en eau peu profonde, Revue Européenne des Eléments Finis. Revue Européenne des Éléments Finis, 2003, 12 (2-3), pp.361-371. ⟨hal-01023273⟩ Plus de détails...
Eric Serre, Peter K. Stansby, Dominique R. Laurence, Brian Launder. Ecoulement autour d'un modèle d'île conique en eau peu profonde, Revue Européenne des Eléments Finis. Revue Européenne des Éléments Finis, 2003, 12 (2-3), pp.361-371. ⟨hal-01023273⟩
Said Benjeddou, Eric Serre, Claude Rey. Application de l'approximation polytropique à la simulation numérique directe d'écoulements de gaz chauds. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2003, 332, pp.271-277. ⟨hal-01023274⟩ Plus de détails...
Said Benjeddou, Eric Serre, Claude Rey. Application de l'approximation polytropique à la simulation numérique directe d'écoulements de gaz chauds. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2003, 332, pp.271-277. ⟨hal-01023274⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Eric Serre, Serge Gauthier. An auto-adative multidomain pseudo-spectral technique for linear stability analysis: application to viscous compressible flows. Journal of Scientific Computing, 2002, 17 (1-4), pp.91-99. ⟨hal-01023182⟩ Plus de détails...
Eric Serre, Serge Gauthier. An auto-adative multidomain pseudo-spectral technique for linear stability analysis: application to viscous compressible flows. Journal of Scientific Computing, 2002, 17 (1-4), pp.91-99. ⟨hal-01023182⟩
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Spiral and wavy vortex flows in short counter-rotating Taylor-Couette cells. International Journal of Theoretical and Computational Fluid dynamics, 2002, 16, pp.5-15. ⟨hal-01023184⟩ Plus de détails...
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Spiral and wavy vortex flows in short counter-rotating Taylor-Couette cells. International Journal of Theoretical and Computational Fluid dynamics, 2002, 16, pp.5-15. ⟨hal-01023184⟩
Journal: International Journal of Theoretical and Computational Fluid dynamics
Ewa Tuliszka-Sznitko, Eric Serre, Patrick Bontoux. On the nature of the boundary layer instability in a closed rotor-stator cavity. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2002, 329, pp.91-99. ⟨hal-01023180⟩ Plus de détails...
Ewa Tuliszka-Sznitko, Eric Serre, Patrick Bontoux. On the nature of the boundary layer instability in a closed rotor-stator cavity. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2002, 329, pp.91-99. ⟨hal-01023180⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Isabelle Raspo, Sandrine Hugues, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. Spectral projection methods for the simulation of complex three-dimensional rotating flows. Computers and Fluids, 2002, 31 (4-7), pp.745-767. ⟨hal-01023173⟩ Plus de détails...
Isabelle Raspo, Sandrine Hugues, Eric Serre, Anthony Randriamampianina, Patrick Bontoux. Spectral projection methods for the simulation of complex three-dimensional rotating flows. Computers and Fluids, 2002, 31 (4-7), pp.745-767. ⟨hal-01023173⟩
Eric Serre, Patrick Bontoux. Vortex breakdown in a three-dimensional swirling flow. Journal of Fluid Mechanics, 2002, 459, pp.347-370. ⟨hal-01023166⟩ Plus de détails...
D.V. Lyubimov, T. P. Lyubimova, R.V. Skuridin, G. Chen, B. Roux. Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions. Computers and Fluids, 2002, 31, pp.663-682. ⟨10.1016/S0045-7930(01)00078-0⟩. ⟨hal-01307320⟩ Plus de détails...
This paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the absence of vibrations the bridge is cylindrical; but due to vibration the mean shape of the meniscus is no more cylindrical and the meniscus oscillates around this mean shape. Two models are developed. First, we take into account the pulsating deformations of the meniscus (free surface), but we assume that the mean shape of meniscus remains cylindrical (i.e., we neglect the influence of vibration on this mean shape). For this simple case, a solution of the problem for the pulsating meniscus deformations and the pulsating velocity field is found in explicit form. For the mean flow, the problem is solved numerically by a finite-difference method. The calculations demonstrate the contribution of two basic mechanisms of mean flow generation due to vibrations, related to the generation of mean vorticity in the viscous boundary layer near the rigid boundaries and surface-wave propagation at a free surface. The intensity of the mean flow induced by surface waves is found to be sharply increasing when the vibration frequency approaches the resonance values that are determined from the explicit form of the solution of pulsation problem. In the second model, we take into account both pulsating and mean deformations of the meniscus. The governing equations for the potential of pulsating velocity and mean velocity, and for the pressure, are solved by using a finite-difference method and a boundary-fitted curvilinear coordinate system fitting the free surface.
D.V. Lyubimov, T. P. Lyubimova, R.V. Skuridin, G. Chen, B. Roux. Numerical investigation of meniscus deformation and flow in an isothermal liquid bridge subject to high-frequency vibrations under zero gravity conditions. Computers and Fluids, 2002, 31, pp.663-682. ⟨10.1016/S0045-7930(01)00078-0⟩. ⟨hal-01307320⟩
Eric Serre, Patrick Bontoux. Eclatement tourbillonnaire dans une cavité rotor-stator cylindrique. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2001, 329, pp.727-733. ⟨hal-01023151⟩ Plus de détails...
Eric Serre, Patrick Bontoux. Eclatement tourbillonnaire dans une cavité rotor-stator cylindrique. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2001, 329, pp.727-733. ⟨hal-01023151⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Eric Serre, Jean-Pierre Pulicani. A 3D pseudospectral method for rotating flows is a cylinder. Computers and Fluids, 2001, 30 (4), pp.491-519. ⟨hal-01024303⟩ Plus de détails...
Eric Serre, Jean-Pierre Pulicani. A 3D pseudospectral method for rotating flows is a cylinder. Computers and Fluids, 2001, 30 (4), pp.491-519. ⟨hal-01024303⟩
Sofiane Meradji, Tp Lyubimova, Dv Lyubimov, B Roux. Numerical simulation of a liquid drop freely oscillating. Crystal Research and Technology, 2001, 36 (7), pp.729--744. ⟨hal-01291555⟩ Plus de détails...
Sofiane Meradji, Tp Lyubimova, Dv Lyubimov, B Roux. Numerical simulation of a liquid drop freely oscillating. Crystal Research and Technology, 2001, 36 (7), pp.729--744. ⟨hal-01291555⟩
Eric Serre, Patrick Bontoux, Richard Kotarba. Numerical Simulation of the transition in three-dimensional rotating flows with walls. Boundary layer instabilities. International Journal of Computational Fluid Dynamics, 2001, 5 (2), pp.873-879. ⟨hal-01023068⟩ Plus de détails...
Eric Serre, Patrick Bontoux, Richard Kotarba. Numerical Simulation of the transition in three-dimensional rotating flows with walls. Boundary layer instabilities. International Journal of Computational Fluid Dynamics, 2001, 5 (2), pp.873-879. ⟨hal-01023068⟩
Journal: International Journal of Computational Fluid Dynamics
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Direct numerical simulation and identification of complex flows in Taylor-Couette counter-rotating cavities. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2001, 329, pp.727-733. ⟨hal-01023161⟩ Plus de détails...
Olivier Czarny, Eric Serre, Patrick Bontoux, Richard M. Lueptow. Direct numerical simulation and identification of complex flows in Taylor-Couette counter-rotating cavities. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 2001, 329, pp.727-733. ⟨hal-01023161⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Eric Serre, Isabelle Raspo, Patrick Bontoux, Roger Peyret. Spectral solutions of the Navier-Stokes equations for rotating flow,. Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2001, 81 (1), pp.533-536. ⟨hal-01023113⟩ Plus de détails...
Eric Serre, Isabelle Raspo, Patrick Bontoux, Roger Peyret. Spectral solutions of the Navier-Stokes equations for rotating flow,. Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2001, 81 (1), pp.533-536. ⟨hal-01023113⟩
Journal: Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik
Eric Serre, Patrick Bontoux. Three-dimensional swirling flow with a precessing vortex breakdown in a rotor-stator cylinder. Physics of Fluids, 2001, 13 (11), pp.3500-3503. ⟨hal-01023121⟩ Plus de détails...
Eric Serre, Patrick Bontoux. Three-dimensional swirling flow with a precessing vortex breakdown in a rotor-stator cylinder. Physics of Fluids, 2001, 13 (11), pp.3500-3503. ⟨hal-01023121⟩
Eric Serre, Emilia Crespo del Arco, Patrick Bontoux. Annular and spiral patterns in flows between rotating and stationary discs. Journal of Fluid Mechanics, 2001, 434, pp.65-100. ⟨hal-01023110⟩ Plus de détails...
Different instabilities of the boundary layer flows that appear in the cavity between stationary and rotating discs are investigated using three-dimensional direct numerical simulations. The influence of curvature and confinement is studied using two geometrical configurations: (i) a cylindrical cavity including the rotation axis and (ii) an annular cavity radially confined by a shaft and a shroud. The numerical computations are based on a pseudo-spectral Chebyshev{Fourier method for solving the incompressible Navier{Stokes equations written in primitive variables. The high level accuracy of the spectral methods is imperative for the investigation of such instability structures. The basic flow is steady and of the Batchelor type. At a critical rotation rate, stationary axisymmetric and/or three-dimensional structures appear in the B¨odewadt and Ekman layers while at higher rotation rates a second transition to unsteady flow is observed. All features of the transitions are documented. A comparison of the wavenumbers, frequencies, and phase velocities of the instabilities with available theoretical and experimental results shows that both type II (or A) and type I (or B) instabilities appear, depending on flow and geometric control parameters. Interesting patterns exhibiting the coexistence of circular and spiral waves are found under certain conditions.
Eric Serre, Emilia Crespo del Arco, Patrick Bontoux. Annular and spiral patterns in flows between rotating and stationary discs. Journal of Fluid Mechanics, 2001, 434, pp.65-100. ⟨hal-01023110⟩
Dv Lyubimov, Tp Lyubimova, Sofiane Meradji, Bernard Roux, D Beysens, et al.. 2D unsteady motion and deformation of a gaseous bubble in a vibrating liquid at zero gravity. Journal de Physique IV Proceedings, 2001, 11 (PR6), pp.Pr6--91. ⟨hal-01291556⟩ Plus de détails...
Dv Lyubimov, Tp Lyubimova, Sofiane Meradji, Bernard Roux, D Beysens, et al.. 2D unsteady motion and deformation of a gaseous bubble in a vibrating liquid at zero gravity. Journal de Physique IV Proceedings, 2001, 11 (PR6), pp.Pr6--91. ⟨hal-01291556⟩
Eric Serre, Sandrine Hugues, Emilia Crespo del Arco, Anthony Randriamampianina, Patrick Bontoux. Axisymmetric and three-dimensional instabilities in an Ekman boundary layer flow. International Journal of Heat and Fluid Flow, 2001, 22 (1), pp.82-93. ⟨hal-01023080⟩ Plus de détails...
Eric Serre, Sandrine Hugues, Emilia Crespo del Arco, Anthony Randriamampianina, Patrick Bontoux. Axisymmetric and three-dimensional instabilities in an Ekman boundary layer flow. International Journal of Heat and Fluid Flow, 2001, 22 (1), pp.82-93. ⟨hal-01023080⟩
Journal: International Journal of Heat and Fluid Flow
Eric Serre, Isabelle Raspo, Patrick Bontoux. High order accurate spectral approximation for Navier-Stokes problems. Nonlinear Analysis: Theory, Methods and Applications, 2001, 47 (6), pp.4257-4268. ⟨hal-01023116⟩ Plus de détails...
Eric Serre, Isabelle Raspo, Patrick Bontoux. High order accurate spectral approximation for Navier-Stokes problems. Nonlinear Analysis: Theory, Methods and Applications, 2001, 47 (6), pp.4257-4268. ⟨hal-01023116⟩
Journal: Nonlinear Analysis: Theory, Methods and Applications
Christelle Seror, Pierre Sagaut, Christophe Bailly, Daniel Juvé. Subgrid-Scale Contribution to Noise Production in Decaying Isotropic Turbulence. AIAA Journal, 2000, 38 (10), pp.1795-1803. ⟨10.2514/2.860⟩. ⟨hal-02431555⟩ Plus de détails...
Christelle Seror, Pierre Sagaut, Christophe Bailly, Daniel Juvé. Subgrid-Scale Contribution to Noise Production in Decaying Isotropic Turbulence. AIAA Journal, 2000, 38 (10), pp.1795-1803. ⟨10.2514/2.860⟩. ⟨hal-02431555⟩
Eric Serre, Emilia Crespo del Arco, Patrick Bontoux. Instabilité tridimensionnelle dans une cavité inter-disque de type rotor-stator. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 1999, 326, pp.1139-1146. ⟨hal-01024305⟩ Plus de détails...
Eric Serre, Emilia Crespo del Arco, Patrick Bontoux. Instabilité tridimensionnelle dans une cavité inter-disque de type rotor-stator. Comptes rendus de l’Académie des sciences. Série IIb, Mécanique, 1999, 326, pp.1139-1146. ⟨hal-01024305⟩
Journal: Comptes rendus de l’Académie des sciences. Série IIb, Mécanique
Dv Lyubimov, Tp Lyubimova, Sofiane Meradji, B Roux. Vibrational control of crystal growth from liquid phase. Journal of Crystal Growth, 1997, 180 (3), pp.648--659. ⟨hal-01291557⟩ Plus de détails...
Dv Lyubimov, Tp Lyubimova, Sofiane Meradji, B Roux. Vibrational control of crystal growth from liquid phase. Journal of Crystal Growth, 1997, 180 (3), pp.648--659. ⟨hal-01291557⟩
Jean Marc Vanel, Roger Peyret, Patrick Bontoux. A pseudo-spectral solution of vorticity-stream function equations using the influence matrix technique. Morton K W and Baines M J. Numerical Methods for Fluid Dynamics II, Clarendon Press Oxford, pp.463-475, 1986. ⟨hal-00974966⟩ Plus de détails...
A method for computing unsteady two dimensional incompressible flows, using the vorticity and the stream function as dependent variables approximated by Chebyshev polynomial expansions is presented. Boundary conditions for the vorticity are derived by the influence matrix technique. The theoretical and numerical difficulties associated with the two-dimensional formulation of the method are discussed. Numerical results illustrate the properties of the method.
Jean Marc Vanel, Roger Peyret, Patrick Bontoux. A pseudo-spectral solution of vorticity-stream function equations using the influence matrix technique. Morton K W and Baines M J. Numerical Methods for Fluid Dynamics II, Clarendon Press Oxford, pp.463-475, 1986. ⟨hal-00974966⟩
