Ecoulements en rotation : Taylor-Couette, Taylor-Couette Poiseuille, Instabilités baroclines et stratorotationnelles
Simulations directes et des grandes échelles turbulentes : jet impactant un disque en rotation
Simulations autour de corps déformables: application à la nage des poissons
Méthodes numériques d'ordre élevé
Axe de recherche :
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Effets thermiques dans les systèmes en rotation (voir les détails sur la page dédiée)
Publications scientifiques au M2P2
2018
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. LES in a Concentric Annular Pipe: Analysis of Mesh Sensitivity and Wall Pressure Fluctuations. Direct and Large-Eddy Simulation X, pp.93-100, 2018, 978-3-319-63211-7. ⟨hal-02111988⟩ Plus de détails...
Annular pipe flows have varied application in the domains of nuclear reactors, heat exchangers, drilling operations in oil industry etc.
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. LES in a Concentric Annular Pipe: Analysis of Mesh Sensitivity and Wall Pressure Fluctuations. Direct and Large-Eddy Simulation X, pp.93-100, 2018, 978-3-319-63211-7. ⟨hal-02111988⟩
Stéphane Abide, Stéphane Viazzo, Isabelle Raspo, Anthony Randriamampianina. Higher-order compact scheme for high-performance computing of stratified rotating flows. Computers and Fluids, 2018, 174, pp.300-310. ⟨10.1016/j.compfluid.2018.07.016⟩. ⟨hal-02111489⟩ Plus de détails...
To take advantage of modern generation computing hardware, a scalable numerical method, based on higher-order compact scheme, is described to solve rotating stratified flows in cylindrical annular domains. An original approach combining 2d-pencil decomposition and reduced Parallel Diagonal Dominant is proposed to improve the parallelization performance during the computation of Poisson/Helmholtz solvers and time explicit terms. The developed technique is validated with respect to analytical solutions, using the method of manufactured solutions, and available data for two specific configurations. The purpose is to demonstrate its ability to correctly capture the flow characteristics in strato-rotational instability and in baroclinic instability with associated small-scale features. Moreover, this code is found to drastically reduce the huge execution times often preventing detailed numerical investigations of these complex phenomena. Strong scaling test is carried out to assess the performance for up to 1024 cores using grid up to 128 × 568 × 568 in radial, axial and azimuthal directions.
Stéphane Abide, Stéphane Viazzo, Isabelle Raspo, Anthony Randriamampianina. Higher-order compact scheme for high-performance computing of stratified rotating flows. Computers and Fluids, 2018, 174, pp.300-310. ⟨10.1016/j.compfluid.2018.07.016⟩. ⟨hal-02111489⟩
Thomas von Larcher, Stéphane Viazzo, Uwe Harlander, Miklos Vincze, Anthony Randriamampianina. Instabilities and small-scale waves within the Stewartson layers of a thermally driven rotating annulus. Journal of Fluid Mechanics, 2018, 841, pp.380 - 407. ⟨10.1017/jfm.2018.10⟩. ⟨hal-02116196⟩ Plus de détails...
We report on small-scale instabilities in a thermally driven rotating annulus filled with a liquid with moderate Prandtl number. The study is based on direct numerical simulations and an accompanying laboratory experiment. The computations are performed independently with two different flow solvers, that is, first, the non-oscillatory forward-in-time differencing flow solver EULAG and, second, a higher-order finite-difference compact scheme (HOC). Both branches consistently show the occurrence of small-scale patterns at both vertical sidewalls in the Stewartson layers of the annulus. Small-scale flow structures are known to exist at the inner sidewall. In contrast, short-period waves at the outer sidewall have not yet been reported. The physical mechanisms that possibly trigger these patterns are discussed. We also debate whether these small-scale structures are a gravity wave signal.
Thomas von Larcher, Stéphane Viazzo, Uwe Harlander, Miklos Vincze, Anthony Randriamampianina. Instabilities and small-scale waves within the Stewartson layers of a thermally driven rotating annulus. Journal of Fluid Mechanics, 2018, 841, pp.380 - 407. ⟨10.1017/jfm.2018.10⟩. ⟨hal-02116196⟩
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. Comparative study of the contribution of various PWR spacer grid components to hydrodynamic and wall pressure characteristics. Nuclear Engineering and Design, 2017, 317, pp.22-43. ⟨10.1016/j.nucengdes.2017.03.011⟩. ⟨hal-01590274⟩ Plus de détails...
Flow-induced vibrations in a pressurized water reactor (PWR) core can cause fretting wear in fuel rods. These vibrations can compromise safety of a nuclear reactor. So, it is necessary to know the random fluctuating forces acting on the rods which cause these vibrations. In this paper, simplified 3D models like square spacer grid, circular spacer grid and symmetric mixing vanes have been used inside an annular pipe. Hydrodynamic and wall pressure characteristics are evaluated using large eddy simulations (LES). Structured meshes are generated as far as possible. Simulations are compared with an experiment. Results show that the grid and vanes have a combined effect: grid accelerates the flow whereas the vanes contribute to the swirl structures. Spectral analysis of the simulations illustrate vortex shedding phenomenon in the wake of spacer grids. This initial study opens up interesting perspectives towards improving the modeling strategy and understanding the complex phenomenon inside a PWR core.
Saptarshi Bhattacharjee, Guillaume Ricciardi, Stéphane Viazzo. Comparative study of the contribution of various PWR spacer grid components to hydrodynamic and wall pressure characteristics. Nuclear Engineering and Design, 2017, 317, pp.22-43. ⟨10.1016/j.nucengdes.2017.03.011⟩. ⟨hal-01590274⟩
Thomas von Larcher, Stéphane Viazzo, Uwe Harlander, Miklos Vincze, Anthony Randriamampianina. Instabilities and small−scale waves within the Stewartson layers of the thermally driven rotating annulus
. Journal of Fluid Mechanics, In press. ⟨hal-01670784⟩ Plus de détails...
Thomas von Larcher, Stéphane Viazzo, Uwe Harlander, Miklos Vincze, Anthony Randriamampianina. Instabilities and small−scale waves within the Stewartson layers of the thermally driven rotating annulus
. Journal of Fluid Mechanics, In press. ⟨hal-01670784⟩
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
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⟩
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
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
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
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
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⟩
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, 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
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
Héctor Barrios-Pina, Stéphane Viazzo, Claude Rey. A numerical study of laminar and transitional mixed convection flow over a backward-facing step. Computers and Fluids, 2012, 56 (1-2), pp.77-91. ⟨10.1016/j.compfluid.2011.11.016⟩. ⟨hal-01299345⟩ Plus de détails...
This work focuses on the study of the transition from steady to chaotic behavior in mixed convection flow over a backward-facing step. Direct numerical simulations are performed in a two-dimensional horizontal channel of expansion ratio ER = 2 at step level. The effects of the temperature difference between the heated bottom wall and the inflow temperature are investigated by keeping constant the Richardson number at 1. The covered range of Grashof and Reynolds numbers is respectively 3.31 × 104 ⩽ Gr ⩽ 2.72 × 105 and 182.03 ⩽ Re ⩽ 521.34. The thermal and dynamical instabilities which cause the onset of unsteady flow are described in detail. A spectral and phase portrait analysis of the temperature time series allows us to observe that the transition from steady to chaotic flow occurs by period-doubling bifurcations.
Héctor Barrios-Pina, Stéphane Viazzo, Claude Rey. A numerical study of laminar and transitional mixed convection flow over a backward-facing step. Computers and Fluids, 2012, 56 (1-2), pp.77-91. ⟨10.1016/j.compfluid.2011.11.016⟩. ⟨hal-01299345⟩
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⟩
