A safe separation distance (SSD) needs to be considered during firefighting activities (fire suppression or people evacuation) against wildfires. The SSD is of critical interest for both humans and assets located in the wildland-urban interfaces (WUI). In most cases, the safety zone models and guidelines assume a flat terrain and only radiant heating. Nevertheless, injuries or damage do not result exclusively from radiant heating. Indeed, convection must be also considered as a significant contribution of heat transfer, particularly in the presence of the combined effects of sloping terrain and a high wind velocity. In this work, a critical case study is considered for the village of Sari-Solenzara in Corsica (France). This site location was selected by the operational staff since highintensity fire spread is likely to occur in the WUI during wind-blown conditions. This study was carried out for 4 m high shrubland, a sloping terrain of 12° and a wind speed of 16.6 m/s. The numerical simulations were performed using a fully physical fire model, namely, FireStar2D, to investigate a case of fire spreading, which is thought to be representative of most high wildfire risk situations in Corsica. This study is based on the evaluation of the total (radiative and convective) heat flux received by two types of targets (human bodies and buildings) located ahead of the fire front. The results obtained revealed that the radiation was the dominant heat transfer mode in the evaluation of the SSD. In addition, the predictions were consistent with the criterion established by the operational experts, which assumes that in Corsica, a minimum SSD of 50 m is required to keep an equipped firefighter without injury in a fuelbreak named ZAL. This numerical work also provides correlations relating the total heat flux to the SSD.
Jacky Fayad, Gilbert Accary, Frédéric Morandini, François-Joseph Chatelon, Lucile Rossi, et al.. Numerical Assessment of Safe Separation Distance in the Wildland-Urban Interfaces. Fire, 2023, 6 (209), ⟨10.3390/fire6050209⟩. ⟨hal-04101026⟩
Jacky Fayad, Morandini Frédéric, Gilbert Accary, François-Joseph Chatelon, Clément Wandon, et al.. A Study of Two High Intensity Fires across Corsican Shrubland. Atmosphere, 2023, ⟨10.3390/atmos14030473⟩. ⟨hal-04007587⟩ Plus de détails...
This paper reports two experimental fires conducted at field-scale in Corsica, across a particular mountain shrubland. The orientation of the experimental plots was chosen in such a way that the wind was aligned along the main slope direction in order to obtain a high intensity fire. The first objective was to study the high intensity fire behavior by evaluating the propagation conditions related to its speed and intensity, as well as the geometry of the fire front and its impact on different targets. Therefore, an experimental protocol was designed to determine the properties of the fire spread using UAV cameras and its impact using heat flux gauges. Another objective was to study these experiments numerically using a fully physical fire model, namely FireStar3D. Numerical results concerning the fire dynamics, particularly the ROS, were also compared to other predictions of the FireStar2D model. The comparison with experimental measurements showed the robustness of the 3D approach with a maximum difference of 5.2% for the head fire ROS. The fire intensities obtained revealed that these experiments are representative of high intensity fires, which are very difficult to control in the case of real wildfires. Other parameters investigated numerically (flame geometry and heat fluxes) were also in fairly good agreement with the experimental measurements and confirm the capacity of FireStar3D to predict surface fires of high intensity.
Jacky Fayad, Morandini Frédéric, Gilbert Accary, François-Joseph Chatelon, Clément Wandon, et al.. A Study of Two High Intensity Fires across Corsican Shrubland. Atmosphere, 2023, ⟨10.3390/atmos14030473⟩. ⟨hal-04007587⟩
François Joseph Chatelon, Jacques Henri Balbi, Miguel Cruz, Dominique Morvan, Jean Louis Rossi, et al.. Extending the Balbi fire spread Model for field scale conditions: the case of shrubland fires. International Journal of Wildland Fire, 2022, 31 (2), pp.176-192. ⟨10.1071/WF21082⟩. ⟨hal-04064057⟩ Plus de détails...
The 'Balbi model' is a simplified rate of fire spread model aimed at providing fast and accurate simulations for fire spread that can be used by fire managers under operational conditions. This model describes the steady-state spread rate of surface fires by accounting for both radiation and convection heat transfer processes. In the present work the original Balbi model developed for laboratory conditions is improved with changes that address specificities of outdoor fires, such as fuel complexes with a mix of live and dead materials, a larger scale and an open environment. The model is calibrated against a small training dataset (n=25) of shrubland fires conducted in Turkey. A sensitivity analysis of model output is presented and its predictive capacity against a larger independent dataset of experimental fires in shrubland fuels
François Joseph Chatelon, Jacques Henri Balbi, Miguel Cruz, Dominique Morvan, Jean Louis Rossi, et al.. Extending the Balbi fire spread Model for field scale conditions: the case of shrubland fires. International Journal of Wildland Fire, 2022, 31 (2), pp.176-192. ⟨10.1071/WF21082⟩. ⟨hal-04064057⟩
François Joseph Chatelon, Jacques-Henri Balbi, Jacky Fayad, Jean-Louis Rossi, Dominique Morvan, et al.. Physical modelling of fires spreading upslope, involved in fire eruption triggering. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1740-1746, 2022, ⟨10.14195/978-989-26-2298-9_268⟩. ⟨hal-03875354⟩ Plus de détails...
Eruptive fires are one category of extreme fire behaviour. They are characterized by a sudden and unpredictable change in the fire behaviour which represents an extreme danger for people involved in firefighting. The major point is about the mechanism that turns a usual fire behaviour into an eruptive fire behaviour. Among the different explanations found in the literature, the pioneering interpretation consisting in a feedback effect caused by the convective flow induced by the fire under wind and/or slope conditions, has never been disproved with an example of fire accident. The main goal of this work lies in proposing a physical modelling of this fire induced wind. This modelling attempt is derived from the brand-new version of the Balbi model, which is a simplified physical model for surface fires at the field scale that explicitly depends on the triangle of fire (fuel bed, wind and slope). This work is a first step to the modelling of fire eruption. The model tries to represent accurately the acceleration of the fire rate of spread propagating on different sloped terrain under no-wind or weak wind conditions. It is tested against three sets of experiments carried out at the laboratory scale without external wind and against a high intensity experimental fire spreading on a steep sloped terrain and conducted under weak wind conditions in the north-western of Corsica. Some statistical tools are used to compare predicted and observed rate of spread (NMSE, Normalized Mean Square Error and MAPE, Mean Absolute Percentage Error) and to understand the model’s under-predictions or over-predictions trends (FB, Fractional Bias).
François Joseph Chatelon, Jacques-Henri Balbi, Jacky Fayad, Jean-Louis Rossi, Dominique Morvan, et al.. Physical modelling of fires spreading upslope, involved in fire eruption triggering. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1740-1746, 2022, ⟨10.14195/978-989-26-2298-9_268⟩. ⟨hal-03875354⟩
Gilbert Accary, Jacky Fayad, François-Joseph Chatelon, Nicolas Frangieh, Carmen Awad, et al.. Simulation of induced-wind-dominated fire on sloping terrain. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.375-380, 2022, ⟨10.14195/978-989-26-2298-9_59⟩. ⟨hal-03875345⟩ Plus de détails...
Using the fully physical model FireStar3D, a numerical simulation of an eruptive fire was carried out for a grassland on a slopping terrain (30° inclination) and a 10 m-open wind speed of 2 m/s. To reproduce the behaviour of a quasi-infinite fire front, periodic conditions were considered in the fireline direction. The simulation highlights the role played by the additional wind induced by the fire (that reaches about 5.8 m/s at 10 m above ground) and its feedback action on fire behaviour. This interaction results in the transition of the fire behaviour from a plume-dominated fire to a wind-dominated fire, and this goes along with a substantial increase of the rate of spread (from 0.454 m/s to 0.714 m/s) and of the fireline heat release rate (from 4.8 MW/m to 14 MW/m). The fire regime was characterized by Byram’s convection number, based on the effective crosswind speed, that drops from 46.8 to about 3.8 once fire-induced wind takes effect on fire behaviour.
Gilbert Accary, Jacky Fayad, François-Joseph Chatelon, Nicolas Frangieh, Carmen Awad, et al.. Simulation of induced-wind-dominated fire on sloping terrain. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.375-380, 2022, ⟨10.14195/978-989-26-2298-9_59⟩. ⟨hal-03875345⟩
Carmen Awad, Jacky Fayad, Nicolas Frangieh, Frédéric Morandini, Jean Louis Rossi, et al.. Impact of the bulk density on fire spread through a homogenous vegetation layer. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1657-1664, 2022, ⟨10.14195/978-989-26-2298-9_254⟩. ⟨hal-03875325⟩ Plus de détails...
The bulk density as definition represents the ratio between the packing ratio and the density of the vegetation. Therefore, it is directly related to the fuel load, the height and to the porosity of the vegetation. In fact, the bulk density plays an important role in fire propagation and behavior. Due to its dependence on the fuel porosity, the bulk density influences heat transfers inside the fuel bed, so, it can affect directly the rate of spread. Or, the bulk density influences also the fire intensity and flame characteristics (residence time, height and depth) due to its dependence of the fuel load and fuel bed height. However, despite the important influence of the bulk density on fire propagation, the literature does not clarify its impact on fire behavior, different points of view can be exanimated. So, the aim of this study is to investigate the role played by the bulk density upon both propagation parameters and heat transfer of a surface fire through a homogeneous vegetation layer. Investigations were conducted numerically using “FireStar2Dâ€, a complete physical model based on multiphase formulation. Also, experimentally, tests were constructed at the university of Corsica at laboratory scale under no wind and no slope condition. In order to study the elementary effect of the bulk density on fire behavior, three different cases were evaluated: (a) variable fuel load with a constant bulk density, (b) variable fuel load and variable bulk density, (c) variable bulk density with a constant fuel load. Case (a) was only studied numerically, the obtained results are in agreement with the literature: the rate of spread increases with the fuel load until a specific value where the ROS becomes independent of it. Case (b) was evaluated numerically and experimentally using a fix fuel bed height. The numerical and the experimental results showed that the ROS is barely affected by both fuel load and bulk density. Finally, the results of the last case, with a constant fuel load, showed numerically the same tendency proposed by Rothermel: the rate of spread reaches a maximum value at an optimal packing ratio that depends of the surface-volume ratio of the vegetation. Or, experimentally the ROS decreases with the increase of the bulk density. Different variables such as the optical thickness, the fire intensity, the residence time, the radiation and convection heat fluxes have been analyzed.
Carmen Awad, Jacky Fayad, Nicolas Frangieh, Frédéric Morandini, Jean Louis Rossi, et al.. Impact of the bulk density on fire spread through a homogenous vegetation layer. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1657-1664, 2022, ⟨10.14195/978-989-26-2298-9_254⟩. ⟨hal-03875325⟩
François Joseph Chatelon, Miguel Cruz, Jacques-Henri Balbi, Jean-Louis Rossi, Jacky Fayad, et al.. A simplified physical propagation model for surface fires designed for an implementation into fire decision making tools. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.67-73, 2022, ⟨10.14195/978-989-26-2298-9_9⟩. ⟨hal-03875331⟩ Plus de détails...
Nowadays, the needs for decision making tools useful for people involved in firefighting and/or in landscape management becomes more and more crucial, especially with the dramatic increase of the fire dangerousness and fire severity. These tools have to be accurate enough and faster than real time. Up to now, simulators and other tools are mainly based on empirical or semi-empirical models but the lack of physics in their formulation is a major flaw. The Balbi model is a simplified physical propagation model for surface fires which explicitly depends on the topography, the wind velocity and several fuel characteristics. It is a set of algebraic equations built from usual physical conservation laws (mass, momentum etc.) with some strong assumptions. This work aims at providing a new version of the Balbi model in which the resolution of the rate of spread (ROS) does not need any iterative method any more. This simplification is helpful in implementing the equations set into a fire propagation simulator or a coupled fire-atmosphere simulator. It needs a complete change in the structure of the model and the predicted ROS was tested at the field scale against 179 shrubland fires (burnt in Australia, South Africa, Turkey, Portugal, Spain, New Zealand) and 178 Australian grassland fires with a very good agreement with the observed ROS. Two statistical tools are used to check this agreement (Normalized Mean Square Error, NMSE and Mean Absolute Percentage Error, MAPE) and the Fractional Bias (FB) aims at understanding when the model over-predicts or under-predicts the ROS. The proposed model is accurate and its model parameters are calibrated against a small training dataset which makes it fully predictive whatever the environmental and topographic conditions and the fuel bed characteristics. Its more simple structure allows it to be a good candidate for the heart of a simulation or land management decision making tool.
François Joseph Chatelon, Miguel Cruz, Jacques-Henri Balbi, Jean-Louis Rossi, Jacky Fayad, et al.. A simplified physical propagation model for surface fires designed for an implementation into fire decision making tools. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.67-73, 2022, ⟨10.14195/978-989-26-2298-9_9⟩. ⟨hal-03875331⟩
Jacky Fayad, Lucile Rossi, Nicolas Frangieh, Carmen Awad, Gilbert Accary, et al.. Numerical study of an experimental high-intensity prescribed fire across Corsican Genista salzmannii vegetation. Fire Safety Journal, 2022, 131, pp.103600. ⟨10.1016/j.firesaf.2022.103600⟩. ⟨hal-04063905⟩ Plus de détails...
This paper reported a high intensity experimental fire conducted during a field-scale experiment on a steep sloped terrain (28°) as part of a winter prescribed burns campaign managed by the local firefighter service in the northwestern region of Corsica. The rate of spread (ROS) of fire, measured using UAV cameras (thermal and visible), was evaluated at 0.45 m/s. The experiment was numerically reproduced using a completely physical 2D model, namely FireStar2D, and the comparison with the experimental measurements mainly concerned the fire ROS and the heat fluxes received by three distant targets placed at the end of the plot. The results analysis shows that the considered fire has a wind-driven regime of propagation with a fire intensity higher than 7 MW/m. The numerical results are in fairly good agreement with the experimental measurements, within 11% difference for the ROS and 5% for the heat fluxes, validating consequently the relevance of the numerical approach to tackle such high-intensity wildfires. Despite the unfavorable wind and humidity conditions for fire propagation (U = 1.67 m/s and RH = 82%), this experiment confirms that such fire can exhibit a dangerous behavior due to the steep slope of the terrain.
Jacky Fayad, Lucile Rossi, Nicolas Frangieh, Carmen Awad, Gilbert Accary, et al.. Numerical study of an experimental high-intensity prescribed fire across Corsican Genista salzmannii vegetation. Fire Safety Journal, 2022, 131, pp.103600. ⟨10.1016/j.firesaf.2022.103600⟩. ⟨hal-04063905⟩
Dominique Morvan, Gilbert Accary, Sofiane Meradji, Nicolas Frangieh. Fifty years of progress in wildland fire modelling: from empirical to fully physical CFD models. Comptes Rendus. Mécanique, 2022, 350 (S1), pp.1-9. ⟨10.5802/crmeca.133⟩. ⟨hal-04063901⟩ Plus de détails...
The aim of this short review is to present the progress made in wildland fire modelling during the last 50 years and the intellectual track followed by wildland fires models, from fully empirical models in the 60s, to semi-empirical ones in the 70s, to fully physical models at the end of the 90s. During the last period, the large diffusion of HPC methods substantially contributed to the development of multiphase formulations applied to wildland fire modelling. Many studies have particularly focused on the effects of various parameters (vegetation, topography, atmosphere) affecting the behaviour of a fire front propagating through a forest fuel layer.
Dominique Morvan, Gilbert Accary, Sofiane Meradji, Nicolas Frangieh. Fifty years of progress in wildland fire modelling: from empirical to fully physical CFD models. Comptes Rendus. Mécanique, 2022, 350 (S1), pp.1-9. ⟨10.5802/crmeca.133⟩. ⟨hal-04063901⟩
Jacky Fayad, Lucile Rossi, Nicolas Frangieh, Carmen Awad, Gilbert Accary, et al.. Numerical study of high intensity experimental field fires across Corsican shrubland vegetation. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1725-1732, 2022, ⟨10.14195/978-989-26-2298-9_266⟩. ⟨hal-03875178⟩ Plus de détails...
Jacky Fayad, Lucile Rossi, Nicolas Frangieh, Carmen Awad, Gilbert Accary, et al.. Numerical study of high intensity experimental field fires across Corsican shrubland vegetation. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.1725-1732, 2022, ⟨10.14195/978-989-26-2298-9_266⟩. ⟨hal-03875178⟩
Thierry Marcelli, Lucile Rossi, Gilbert Accary, Carmen Awad, Antoine Burglin, et al.. GOLIAT, a project to develop tools for firefighting and land use planning. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.234-239, 2022, ⟨10.14195/978-989-26-2298-9_38⟩. ⟨hal-03875377⟩ Plus de détails...
The GOLIAT project is a consortium of academics and firefighting operators and land-use planning professionals of Corsica. One goal of GOLIAT project is to provide four operational decision support tools. To reach this goal, a survey of past fires occurred in Corsica since the twentieth century beginning is made. This inventory contributes to build up a database with a web display interface easy to use as fire patterns history. A fire behavior and impact simulator prototype for vegetation fires, a geolocation tool for hot spots using UAV images, and a guide of good practices of prescribed fires in the undergrowth are building. At the same time, experimental fires are carried out to improve knowledge about high intensity fire and the experimental results were compared to the predictions provided by a complete physical 3D model, namely FireStar3D.
Thierry Marcelli, Lucile Rossi, Gilbert Accary, Carmen Awad, Antoine Burglin, et al.. GOLIAT, a project to develop tools for firefighting and land use planning. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.234-239, 2022, ⟨10.14195/978-989-26-2298-9_38⟩. ⟨hal-03875377⟩
Nicolas Frangieh, Gilbert Accary, Jean-Louis Rossi, Dominique Morvan, François-Joseph Chatelon, et al.. Fuelbreaks design: from CFD modelling to operational tools. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.222-226, 2022, ⟨10.14195/978-989-26-2298-9_36⟩. ⟨hal-03875340⟩ Plus de détails...
Dimensioning a fuelbreak remains always a challenging problem. For a long time, this problem was tackled using an empirical approach from the experience of operational users such as the fire fighters and the foresters. During the last decades, new approaches coming from fire safety engineering have completed the set of tools adapted to study this problem. These tools are all based on physical considerations, more or- less sophisticated. The simplest ones, consist in assimilating the flame as a radiant panel, calculating the distribution of radiant heat flux as a function of the distance separating the flame to a potential target and defining at what distance this heat flux reached a critical threshold level susceptible to produce damages on this target (pain for people or ignition for materials). The most complex ones, consist in solving the conservation equations (mass, momentum, energy ...) governing the behaviour of complex coupled problem formed by the vegetation, the flame front and the surrounding atmosphere. This new generation of engineering tool, based on CFD approach allows to directly predict the behaviour of a fire front propagating toward a fuelbreak, in order to evaluate its efficiency as a function of the amount of surface fuel (grass, shrubs) removed to reduce locally the fuel load and therefore the intensity of an incoming fire. These two approaches are fully complementary, only the first one has the potentiality to be spread operationally on the field, whereas the second one can contribute to improve the first one and to study with more detail some very sensitive situations such as those encountered in the wildland urban interface (WUI). The main part of this study concerns numerical simulations of the propagation of a fire front through a homogeneous vegetation layer (a grassland) in the vicinity of a fuelbreak represented by a band more or less wide inside which all the fuel was removed. The simulations were performed using a fully physical wildfire model (FIRESTAR3D), three variable parameters were considered in this study: the 1m open wind speed (U1 ranged between 3 and 10 m/s), the fuel height (HFuel ranged between 0.25 and 1m) and the fuelbreak width (LFB). With these conditions, the simulations covered a large range of values of the Byram’s convective number NC (0.3 < NC < 60) in order to explore wind as well driven fires (NC < 2) and plume dominated fires (NC > 10). The 72 simulations carried out in this study have been classified in three categories: 1/ Propagation (if the fire has crossed the fuelbreak with a propagation after); 2/ Overshooting or Marginal (if the fire has crossed the fuelbreak without a propagation after); 3/ No-propagation (if the fuelbreak has stopped the fire). The main objective of this study was to determine the optimal fuelbreak width LFBx separating between the Propagation and the No-propagation regimes, in order to generalize the conclusion, the results have been presented in dimensionless form (similitude theory) in representing as an example the ratio LFBx/HFuel versus the Byram’s convective number NC.
Nicolas Frangieh, Gilbert Accary, Jean-Louis Rossi, Dominique Morvan, François-Joseph Chatelon, et al.. Fuelbreaks design: from CFD modelling to operational tools. Advances in Forest Fire Research 2022, 1.ª Edição, Imprensa da Universidade de Coimbra, pp.222-226, 2022, ⟨10.14195/978-989-26-2298-9_36⟩. ⟨hal-03875340⟩
Nicolas Frangieh, Gilbert Accary, Jean-Louis Rossi, Dominique Morvan, Sofiane Meradji, et al.. Fuelbreak effectiveness against wind-driven and plume-dominated fires: a 3D numerical study. Fire Safety Journal, 2021, pp.103383. ⟨10.1016/j.firesaf.2021.103383⟩. ⟨hal-03597349⟩ Plus de détails...
The effectiveness of a fuelbreak, created in a homogeneous grassland on a flat terrain, was studied numerically. The analysis relies on 3D numerical simulations that were performed using a detailed physical-fire-model (FIRESTAR3D) based on a multiphase formulation. To avoid border effects, calculations were carried out by imposing periodic boundary conditions along the two lateral sides of the computational domain, reproducing that way a quasi-infinitely long fire front. A total of 72 simulations were carried out for various wind speeds, fuel heights, and fuelbreak widths, which allowed to cover a large spectrum of fire behaviour, ranging from plume-dominated fires to wind-driven fires. The results were classified in three main categories: 1- “Propagation” if fire crossed the fuelbreak with a continuous fire front, 2- “Overshooting” and “Marginal” if fire marginally crosses the fuelbreak with the formation of burning pockets, and 3- “No propagation” if fire does not cross at all the fuelbreak. The ratio of fuelbreak width to fuel height, marking the “Propagation”/“No propagation” transition, was found to be scaled with Byram's convection number Nc as 75.07 × Nc−0.46. The numerical results were also compared to an operational wildfire engineering tool (DIMZAL) dedicated to fuelbreaks dimensioning.
Nicolas Frangieh, Gilbert Accary, Jean-Louis Rossi, Dominique Morvan, Sofiane Meradji, et al.. Fuelbreak effectiveness against wind-driven and plume-dominated fires: a 3D numerical study. Fire Safety Journal, 2021, pp.103383. ⟨10.1016/j.firesaf.2021.103383⟩. ⟨hal-03597349⟩
Carmen Awad, Nicolas Frangieh, Thierry Marcelli, Gilbert Accary, Dominique Morvan, et al.. Numerical study of the moisture content threshold under prescribed burning conditions. Fire Safety Journal, 2021, pp.103324. ⟨10.1016/j.firesaf.2021.103324⟩. ⟨hal-03595964⟩ Plus de détails...
The safety during prescribed burnings could be achieved by conducting these operations under marginal conditions of fire propagation. This type of fire can or cannot propagate on account of small deviations of the burning conditions, mainly the wind speed, the fuel load, and the fuel moisture-content. In this context, numerical simulations of grassland fires were conducted under marginal conditions in order to relate the moisturecontent threshold of propagation success to the wind speed and the fuel load. The simulations were conducted using FireStar2D, a complete physical 2D fire simulator based on a multiphase modelling approach. The 10 mopen wind speed ranged from 0 to 10 m/s and the fuel load varied from 0.1 kg/m 2 to 0.7 kg/m 2. The effects of wind speed and fuel moisture-content on the fire behaviour and on the flame parameters are discussed. The results show that the moisture threshold increases with the fuel load until it reaches a value beyond which there is no dependence. A similar dependence of the moisture threshold on the wind speed is also observed. Finally, empirical formulae were constructed to relate the fuel moisture content threshold to the wind speed and the fuel loading implicitly through Byram's convective number.
Carmen Awad, Nicolas Frangieh, Thierry Marcelli, Gilbert Accary, Dominique Morvan, et al.. Numerical study of the moisture content threshold under prescribed burning conditions. Fire Safety Journal, 2021, pp.103324. ⟨10.1016/j.firesaf.2021.103324⟩. ⟨hal-03595964⟩
Gilbert Accary, Duncan Sutherland, Nicolas Frangieh, Khalid Moinuddin, Ibrahim Shamseddine, et al.. Physics-Based Simulations of Flow and Fire Development Downstream of a Canopy. Atmosphere, 2020, 11 (7), pp.683. ⟨10.3390/atmos11070683⟩. ⟨hal-02957445⟩ Plus de détails...
The behavior of a grassland fire propagating downstream of a forest canopy has been simulated numerically using the fully physics-based wildfire model FIRESTAR3D. This configuration reproduces quite accurately the situation encountered when a wildfire spreads from a forest to an open grassland, as can be the case in a fuel break or a clearing, or during a prescribed burning operation. One of the objectives of this study was to evaluate the impact of the presence of a canopy upstream of a grassfire, especially the modifications of the local wind conditions before and inside a clearing or a fuel break. The knowledge of this kind of information constitutes a major element in improving the safety conditions of forest managers and firefighters in charge of firefighting or prescribed burning operations in such configurations. Another objective was to study the behavior of the fire under realistic turbulent flow conditions, i.e., flow resulting from the interaction between an atmospheric boundary layer (ABL) with a surrounding canopy. Therefore, the study was divided into two phases. The first phase consisted of generating an ABL/canopy turbulent flow above a pine forest (10 m high, 200 m long) using periodic boundary conditions along the streamwise direction. Large Eddy Simulations (LES) were carried out for a sufficiently long time to achieve a quasi-fully developed turbulence. The second phase consisted of simulating the propagation of a surface fire through a grassland, bordered upstream by a forest section (having the same characteristics used for the first step), while imposing the turbulent flow obtained from the first step as a dynamic inlet condition to the domain. The simulations were carried out for a wind speed that ranged between 1 and 12 m/s; these values have allowed the simulations to cover the two regimes of propagation of surfaces fires, namely plume-dominated and wind-driven fires.
Gilbert Accary, Duncan Sutherland, Nicolas Frangieh, Khalid Moinuddin, Ibrahim Shamseddine, et al.. Physics-Based Simulations of Flow and Fire Development Downstream of a Canopy. Atmosphere, 2020, 11 (7), pp.683. ⟨10.3390/atmos11070683⟩. ⟨hal-02957445⟩
Nicolas Frangieh, Gilbert Accary, Dominique Morvan, Sofiane Meradji, Oleg Bessonov. Wildfires front dynamics: 3D structures and intensity at small and large scales. Combustion and Flame, 2020, 211, pp.54-67. ⟨10.1016/j.combustflame.2019.09.017⟩. ⟨hal-02892557⟩ Plus de détails...
The 3D structure of a fire front propagating through a homogeneous porous solid-fuel layer was studied numerically at laboratory and field scales. At laboratory scale, wind-tunnel fires propagating through laser-cut cardboard fuel were numerically reproduced, while at field scale, simulations of grassland fires with quasi-infinite fire front were carried out for different wind speeds. These simulations were performed using FIRESTAR3D, based on a multiphase formulation that includes the main physical phenomena governing fire behavior. An unsteady RANS approach and a Large Eddy Simulation (LES) approach were used to simulate the reactive turbulent flow, whereas turbulent combustion was modeled using Eddy Dissipation Concept (EDC). Unlike other 3D wildfire tools available in the community, such as FIRETEC and WFDS, the model is based on an implicit, low-Mach number resolution of the governing equations, and makes no empirical assumptions in the resolution of the radiative transfer equation. The comparison with the experimental data concerned mainly the Rate of Spread (ROS) of fire, the fireline intensity, the flame-zone depth, and the wavelength characterizing the crest-and-trough structure of the fire front along the transverse direction. Particular attention was drawn to the similitude in the fire front dynamics between small and large scales. In order to highlight the physical mechanisms responsible for this dynamics, a dimensional analysis was carried out by introducing Byram's convection number N-C based on the fireline intensity and Froude's numbers Fr based on the characteristic wavelength of the fire-front structure. The analysis shows that all the results (wind-tunnel fires and grassland fires, experimental and numerical) collapsed on a single scaling law in the form Fr = N-C(-)2/3.
Nicolas Frangieh, Gilbert Accary, Dominique Morvan, Sofiane Meradji, Oleg Bessonov. Wildfires front dynamics: 3D structures and intensity at small and large scales. Combustion and Flame, 2020, 211, pp.54-67. ⟨10.1016/j.combustflame.2019.09.017⟩. ⟨hal-02892557⟩
Jacques Henri Balbi, François Joseph Chatelon, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli, et al.. A convective–radiative propagation model for wildland fires. International Journal of Wildland Fire, 2020, ⟨10.1071/WF19103⟩. ⟨hal-02570863⟩ Plus de détails...
Jacques Henri Balbi, François Joseph Chatelon, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli, et al.. A convective–radiative propagation model for wildland fires. International Journal of Wildland Fire, 2020, ⟨10.1071/WF19103⟩. ⟨hal-02570863⟩
Jacques Henri Balbi, François Joseph Chatelon, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli, et al.. A convective–radiative propagation model for wildland fires. International Journal of Wildland Fire, 2020, ⟨10.1071/WF19103⟩. ⟨hal-03251626⟩ Plus de détails...
The 'Balbi model' is a simplified steady-state physical propagation model for surface fires that considers radiative heat transfer from the surface area of burning fuel particles as well as from the flame body. In this work, a completely new version of this propagation model for wildand fires is proposed. Even if, in the present work, this model is confined to laboratory experiments, its purpose is to be used at a larger scale in the field under operational conditions. This model was constructed from a radiative propagation model with the addition of a convective heat transfer term resulting from the impingement of packets of hot reacting gases on unburnt fuel elements located at the base of the flame. The flame inside the fuel bed is seen as the 'fingers of fire' described in the literature. The proposed model is physics-based, faster than real time and fully predictive, which means that model parameters do not change from one experiment to another. The predicted rate of spread is applied to a large set of laboratory experiments (through homogeneous pine needles and excelsior fuel beds) and is compared with the predictions of both a very simple empirical model (Catchpole) and a detailed physical model (FireStar2D).
Jacques Henri Balbi, François Joseph Chatelon, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli, et al.. A convective–radiative propagation model for wildland fires. International Journal of Wildland Fire, 2020, ⟨10.1071/WF19103⟩. ⟨hal-03251626⟩
Nicolas Frangieh, Dominique Morvan, Sofiane Meradji, Gilbert Accary, Oleg Bessonov. Numerical simulation of grassland fires behavior using an implicit physical multiphase model. Fire Safety Journal, 2018, 102, pp.37-47. ⟨10.1016/j.firesaf.2018.06.004⟩. ⟨hal-02114073⟩ Plus de détails...
12 This study reports 3D numerical simulations of the ignition and the propagation of 13 grassland fires. The mathematical model is based on a multiphase formulation and on a 14 homogenization approach that consists in averaging the conservation equations (mass, 15 momentum, energy …) governing the evolution of variables representing the state of the 16 vegetation/atmosphere system, inside a control volume containing both the solid-17 vegetation phase and the surrounding gaseous phase. This preliminary operation results 18 in the introduction of source/sink additional terms representing the interaction between 19 the gaseous phase and the solid-fuel particles. This study was conducted at large scale in 20 grassland because it represents the scale at which the behavior of the fire front presents 21 most similarities with full scale wildfires and also because of the existence of a large 22 number of relatively well controlled experiments performed in Australia and in the 23 United States. The simulations were performed for a tall grass, on a flat terrain, and for 24 six values of the 10-m open wind speed ranged between 1 and 12 m/s. The results are in 25 fairly good agreement with experimental data, with the predictions of operational 26 empirical and semi-empirical models, such as the McArthur model (MK5) in Australia and 27 the Rothermel model (BEHAVE) in USA, as well as with the predictions of other fully 3D 28 physical fire models (FIRETEC and WFDS). The comparison with the literature was 29 mainly based on the estimation of the rate of fire spread (ROS) and of the fire intensity, 30 as well as on the analysis of the fire-front shape. 31 32
Nicolas Frangieh, Dominique Morvan, Sofiane Meradji, Gilbert Accary, Oleg Bessonov. Numerical simulation of grassland fires behavior using an implicit physical multiphase model. Fire Safety Journal, 2018, 102, pp.37-47. ⟨10.1016/j.firesaf.2018.06.004⟩. ⟨hal-02114073⟩
Dominique Morvan, Gilbert Accary, Sofiane Meradji, Nicolas Frangieh, Oleg Bessonov. A 3D physical model to study the behavior of vegetation fires at laboratory scale. Fire Safety Journal, 2018, 101, pp.39-52. ⟨10.1016/j.firesaf.2018.08.011⟩. ⟨hal-02114685⟩ Plus de détails...
A 3D multi-physical model referred to as “FireStar3D” has been developed in order to predict the behavior of wildfires at a local scale (<500 m). In the continuity of a previous work limited to 2D configurations, this model consists of solving the conservation equations of the coupled system composed of the vegetation and the surrounding gaseous medium. In particular, the model is able to account explicitly for all the mechanisms of degradation of the vegetation (by drying, pyrolysis, and heterogeneous combustion) and the various interactions between the gas mixture (ambient air + pyrolysis and combustion products) and the vegetation cover such as drag force, heat transfer by convection and radiation, and mass transfer. Compared to previous works, some new features were introduced in the modeling of the surface combustion of charcoal, the calculation of the heat transfer coefficient between the solid fuel particles and the surrounding atmosphere, and many improvements were brought to the numerical method to enable affordable 3D simulations. The partial validation of the model was based on some comparisons with experimental data collected at small scale fires carried out in the Missoula Fire Sciences Lab's wind tunnel, through various solid-fuel layers and in well controlled conditions. A relative good agreement was obtained for most of the simulations that were conducted. A parametric study of the dependence of the rate of spread on the wind speed and on the fuelbed characteristics is presented.
Dominique Morvan, Gilbert Accary, Sofiane Meradji, Nicolas Frangieh, Oleg Bessonov. A 3D physical model to study the behavior of vegetation fires at laboratory scale. Fire Safety Journal, 2018, 101, pp.39-52. ⟨10.1016/j.firesaf.2018.08.011⟩. ⟨hal-02114685⟩
Mohamad El Houssami, Aymeric Lamorlette, Dominique Morvan, Rory M Hadden, Albert Simeoni. Framework for submodel improvement in wildfire modeling. Combustion and Flame, 2018, 190, pp.12-24. ⟨10.1016/j.combustflame.2017.09.038⟩. ⟨hal-02114000⟩ Plus de détails...
An experimental and numerical study was carried out to assess the performance of the different sub-models and parameters used to describe the burning dynamics of wildfires. A multiphase formulation was used and compared to static fires of dried pitch pine needles of different bulk densities. The samples were exposed to an external heat flux of 50 kW/m 2 in the FM Global Fire Propagation Apparatus and subjected to different airflows, providing a controlled environment and repeatable conditions. Sub-models for convective heat transfer, drag forces, and char combustion were investigated to provide mass loss rate, flaming duration, and gas emissions. Good agreement of predicted mass loss rates and heat release rates was achieved, where all these submodels were selected to suit the tested conditions. Simulated flaming times for different flow conditions and different fuel bulk densities compared favorably against experimental measurements. The calculation of the drag forces and the heat transfer coefficient was demonstrated to influence greatly the heating/cooling rate, the degradation rate, and the flaming time. The simulated CO and CO 2 values compared well with experimental data, especially for reproducing the transition between flaming and smoldering. This study complements a previous study made with no flow to propose a systematic approach that can be used to assess the performance of the submodels and to better understand how specific physical phenomena contribute to the wildfire dynamics. Furthermore, this study underlined the importance of selecting relevant submodels and the necessity of introducing relevant subgrid-scale modelling for larger scale simulations.
Mohamad El Houssami, Aymeric Lamorlette, Dominique Morvan, Rory M Hadden, Albert Simeoni. Framework for submodel improvement in wildfire modeling. Combustion and Flame, 2018, 190, pp.12-24. ⟨10.1016/j.combustflame.2017.09.038⟩. ⟨hal-02114000⟩
Dominique Morvan, Nicolas Frangieh. Wildland fires behaviour: wind effect versus Byram’s convective number and consequences upon the regime of propagation. International Journal of Wildland Fire, 2018, 27 (9), pp.636. ⟨10.1071/Wf18014⟩. ⟨hal-02114689⟩ Plus de détails...
With fuel moisture content and slope, wind velocity (U W) is one of the major physical parameters that most affects the behaviour of wildland fires. The aim of this short paper was to revisit the relationship between the rate of spread (ROS) and the wind velocity, through the role played by the two forces governing the trajectory of the flame front and the plume, i.e. the buoyancy of the plume and the inertia due to wind. A large set of experimental data (at field and laboratory scale) from the literature was analysed, by introducing the ratio between these two forces, namely Byram's convective number N C and considering the relationship between the fire ROS/wind speed ratio and Byram's number. This short note was also an opportunity to make a point on particular issues, such as the existence of two regimes of propagation of surface fires (wind-driven fire vs plume-dominated fire), the relative importance of the two modes of heat transfer (by convection and radiation) on the propagation of a fire front, and others scientific debates animating the wildland fire community.
Dominique Morvan, Nicolas Frangieh. Wildland fires behaviour: wind effect versus Byram’s convective number and consequences upon the regime of propagation. International Journal of Wildland Fire, 2018, 27 (9), pp.636. ⟨10.1071/Wf18014⟩. ⟨hal-02114689⟩
Aymeric Lamorlette, Mohamad El Houssami, Dominique Morvan. An improved non-equilibrium model for the ignition of living fuel. International Journal of Wildland Fire, 2018, 27 (1), pp.29-41. ⟨10.1071/Wf17020⟩. ⟨hal-02114417⟩ Plus de détails...
This paper deals with the modelling of living fuel ignition, suggesting that an accurate description using a multiphase formulation requires consideration of a thermal disequilibrium within the vegetation particle, between the solid (wood) and the liquid (sap). A simple model at particle scale is studied to evaluate the flux distribution between phases in order to split the net flux on the particles into the two sub-phases. An analytical solution for the split function is obtained from this model and is implemented in ForestFireFOAM, a computational fluid dynamics (CFD) solver dedicated to vegetation fire simulations, based on FireFOAM. Using this multiphase formulation, simulations are run and compared with existing data on living fuel flammability. The following aspects were considered: fuel surface temperature, ignition, flaming combustion time, mean and peak heat release rate (HRR). Acceptable results were obtained, suggesting that the thermal equilibrium might not be an acceptable assumption to properly model ignition of living fuel.
Aymeric Lamorlette, Mohamad El Houssami, Dominique Morvan. An improved non-equilibrium model for the ignition of living fuel. International Journal of Wildland Fire, 2018, 27 (1), pp.29-41. ⟨10.1071/Wf17020⟩. ⟨hal-02114417⟩
William Mell, Albert Simeoni, Dominique Morvan, J. Kevin Kevin Hiers, Nicholas Skowronski, et al.. Clarifying the meaning of mantras in wildland fire behaviour modelling: reply to Cruz et al. (2017). International Journal of Wildland Fire, 2018, 27 (11), pp.770. ⟨10.1071/Wf18106⟩. ⟨hal-02114662⟩ Plus de détails...
In a recent communication, Cruz et al. (2017) called attention to several recurring statements (mantras) in the wildland fire literature regarding empirical and physical fire behaviour models. Motivated by concern that these mantras have not been fully vetted and are repeated blindly, Cruz et al. (2017) sought to verify five mantras they identify. This is a worthy goal and here we seek to extend the discussion and provide clarification to several confusing aspects of the Cruz et al. (2017) communication. In particular, their treatment of what they call physical models is inconsistent, neglects to reference current research activity focussed on combined experimentation and model development, and misses an opportunity to discuss the potential use of physical models to fire behaviour outside the scope of empirical approaches.
William Mell, Albert Simeoni, Dominique Morvan, J. Kevin Kevin Hiers, Nicholas Skowronski, et al.. Clarifying the meaning of mantras in wildland fire behaviour modelling: reply to Cruz et al. (2017). International Journal of Wildland Fire, 2018, 27 (11), pp.770. ⟨10.1071/Wf18106⟩. ⟨hal-02114662⟩
François Joseph Chatelon, Jacques Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, 2017, 90, pp.54-61. ⟨10.1016/j.firesaf.2017.04.022⟩. ⟨hal-01590266⟩ Plus de détails...
Several studies in the literature explore the connection between rate of spread (ROS) and wind in wildland fires. These studies show very different positions about the role of radiation and convection as heat transfer mechanisms. In the case when the fuel bed is well-ordered and vertically-oriented, there seems to be a consensus leading to suggest that convective heating is the dominant heat transfer mode in that case. The purpose of this work is to propose a convective semi-physical model for the behaviour of the rate of spread in wind, when the fuel bed is vertically-oriented. Due to a specific fuel bed arrangement, flame radiation -i.e. radiation from the part of the flame above the vegetal stratum is neglected. Only horizontal radiation from the fuel burning particles area and convective heating are taken into account. Convective heat transfer is assumed to be the primary heat transfer mechanism. The proposed model is confronted to 172 laboratory fires with a wide range of fuel characteristics. The predicted results are also compared with two simplified models from the literature. Statistical tools are used to check the agreement between the predicted ROS and the observed one where a strong agreement is generally observed, irrespective of fuel bed characteristics.
François Joseph Chatelon, Jacques Henri Balbi, Dominique Morvan, Jean Louis Rossi, Thierry Marcelli. A convective model for laboratory fires with well-ordered vertically-oriented fuel beds. Fire Safety Journal, 2017, 90, pp.54-61. ⟨10.1016/j.firesaf.2017.04.022⟩. ⟨hal-01590266⟩
Rachael Aganetti, Aymeric Lamorlette, Guilbert Emilie, Dominique Morvan, G.R. Thorpe. Advection and the self-heating of organic porous media. International Journal of Heat and Mass Transfer, 2016, ⟨10.1016/j.ijheatmasstransfer.2015.11.023⟩. ⟨hal-01345737⟩ Plus de détails...
Self-heating is commonly observed when organic materials such as biosolids, coal, food grains and compost are stockpiled. A convection–diffusion model is presented that accounts for the roles of advection and the transport of oxygen in the self-heating process, as well as the development of an empirical correlation between dimensionless Darcy number, Frank–Kamenetskii parameter and pile aspect ratio, to predict the critical permeability above which thermal runaway can be avoided. It is apparent that the permeability of the stockpile determines the likelihood of the thermal runaway. However, the solids that form a stockpile are poly-disperse and it is essential to determine an effective permeability. This has been achieved using experimental data on biosolids obtained from a wastewater treatment plant in Australia. With this method the model is used to demonstrate how the permeability of a stockpile might be adjusted to reduce the incidence of thermal runaway.
Rachael Aganetti, Aymeric Lamorlette, Guilbert Emilie, Dominique Morvan, G.R. Thorpe. Advection and the self-heating of organic porous media. International Journal of Heat and Mass Transfer, 2016, ⟨10.1016/j.ijheatmasstransfer.2015.11.023⟩. ⟨hal-01345737⟩
Journal: International Journal of Heat and Mass Transfer
Mohamad El Houssami, J.C. Thomas, Aymeric Lamorlette, Dominique Morvan, M. Chaos, et al.. Experimental and numerical studies characterizing the burning dynamics of wildland fuels. Combustion and Flame, 2016, 168, pp.113-126. ⟨10.1016/j.combustflame.2016.04.004⟩. ⟨hal-01345741⟩ Plus de détails...
A method to accurately understand the processes controlling the burning behavior of porous wildland fuels is presented using numerical simulations and laboratory experiments. A multiphase approach has been implemented in OpenFOAM, which is based on the FireFOAM solver for large eddy simulations (LES). Conservation equations are averaged in a control volume containing a gas and a solid phase. Drying, pyrolysis, and char oxidation are described by interaction between the two phases. Numerical simulations are compared to laboratory experiments carried out with porous pine needle beds in the FM Global Fire Propagation Apparatus (FPA). These experiments are used to support the use and the development of submodels that represent heat transfer, pyrolysis, gas-phase combustion, and smoldering processes. The model is tested for different bulk densities, two distinct species and two different radiative heat fluxes used to heat up the samples. It has been possible to reproduce mass loss rates, heat release rates, and temperatures that agree with experimental observations, and to highlight the current limitations of the model.
Mohamad El Houssami, J.C. Thomas, Aymeric Lamorlette, Dominique Morvan, M. Chaos, et al.. Experimental and numerical studies characterizing the burning dynamics of wildland fuels. Combustion and Flame, 2016, 168, pp.113-126. ⟨10.1016/j.combustflame.2016.04.004⟩. ⟨hal-01345741⟩
Aymeric Lamorlette, Mohamad El Houssami, Jan C. Thomas, Albert Simeoni, Dominique Morvan. A dimensional analysis of forest fuel layer ignition model: Application to the ignition of pine needle litters. Journal of Fire Sciences, 2015, pp.NC. ⟨10.1177/ToBeAssigned⟩. ⟨hal-01157866⟩ Plus de détails...
This paper deals with the physical modelling of forest fuel layer ignition. A model based on momentum, fluid and solid phase energy equations is written for a fuel layer and a dimensional analysis is performed. This analysis allows to enlighten two relevant dimensionless groups regarding the dimensionless time to ignition of a fuel layer and also provides a suited scaling for the fluid velocity inside the fuel layer during ignition. A correlation for the time to ignition is then fitted on experimental data obtained using a FM-Global Fire Propagation Apparatus (FPA) for different pine species with a closed basket. A good agreement is found, emphasizing the relevance of the dimensionless groups and the thermally thick behaviour of the solid particles during the ignition process under incident radiant heat flux as low as 8 − 12kW.m −2 .
Aymeric Lamorlette, Mohamad El Houssami, Jan C. Thomas, Albert Simeoni, Dominique Morvan. A dimensional analysis of forest fuel layer ignition model: Application to the ignition of pine needle litters. Journal of Fire Sciences, 2015, pp.NC. ⟨10.1177/ToBeAssigned⟩. ⟨hal-01157866⟩
Dominique Morvan. Numerical study of the behaviour of a surface fire propagating through a firebreak built in a Mediterranean shrub layer. Fire Safety Journal, 2015, 71 (7), pp.34-48. ⟨10.1016/j.firesaf.2014.11.012⟩. ⟨hal-01297711⟩ Plus de détails...
The efficiency of a firebreak, built in a shrubland has been studied numerically using a multiphase physical model. The physical mechanisms governing the propagation of the surface fire and the consequences upon the temperature signal and the radiative heat flux received by a target located at 1 m above the ground level, have been firstly studied before positioning the firebreak. The role played by the flame and the recirculation of hot gases to the ignition of unburned fuel (especially the dry grass) ahead of the fire front have been clearly identified. Four values of the firebreak width LC (ranged between 5 and 20 m) and 3 values of wind velocities (ranged between 1 and 8 m/s) have been tested. The simulations show that above a threshold value of this parameter, even if a small amount of the fuel located on the opposite side of the firebreak was ignited, the released energy was not sufficient to sustain the propagation of the surface fire after crossing the firebreak.
Dominique Morvan. Numerical study of the behaviour of a surface fire propagating through a firebreak built in a Mediterranean shrub layer. Fire Safety Journal, 2015, 71 (7), pp.34-48. ⟨10.1016/j.firesaf.2014.11.012⟩. ⟨hal-01297711⟩
Dominique Morvan. Wind effects, unsteady behaviors, and regimes of propagation of surface fires in open field. Combustion Science and Technology, 2014, 186 (7), pp.869-888. ⟨10.1080/00102202.2014.885961⟩. ⟨hal-01049769⟩ Plus de détails...
The subject of this article concerns the unsteady effects (fire intensity, wind) upon the propagation and, more generally, the behavior of surface fires in open fields. The study focused on two sources of unsteadiness: the first one resulting from the regime of propagation (wind driven or plume dominated), which can affect greatly the behavior of the flame front and consequently the fire intensity, the second one resulting from the wind gusts associated with the conditions of flow of wind in real conditions. The study was based on numerical simulations, using a multiphase formulation, and on spectral analysis of the time evolution of the fire line intensity. The calculations were performed in 2D for a homogeneous vegetation layer (grassland) and for a large interval of wind conditions (10 m open wind velocity U10 ranged between 1 m/s and 25 m/s). The results have highlighted the link between the unsteady character of flame front behavior and the regime of propagation (plume dominated, wind driven). A particular interest was focused on the role played by two potential sources of instabilities, namely the Kelvin-Helmholtz instability (wind effects) and the thermo-convective instability (plume effects), upon the behavior of fires. A second set of simulations has been carried out using unsteady wind conditions, reproduced using sinusoidal boundary conditions for the streamwise velocity, with a frequency ranging between 0.5 Hz and 3 Hz.
Dominique Morvan. Wind effects, unsteady behaviors, and regimes of propagation of surface fires in open field. Combustion Science and Technology, 2014, 186 (7), pp.869-888. ⟨10.1080/00102202.2014.885961⟩. ⟨hal-01049769⟩
K. Gavrilov, Dominique Morvan, Gilbert Accary, Dimitry Lyubimov, Sofiane Meradji. Numerical simulation of coherent turbulent structures and of passive scalar dispersion in a canopy sub-layer. Computers and Fluids, 2013, LES of turbulence aeroacoustics and combustion, 78, pp.54-62. ⟨10.1016/j.compfluid.2012.08.021⟩. ⟨hal-01030794⟩ Plus de détails...
This study deals with the problem of turbulent atmospheric boundary-layer flow over a forest canopy. Numerous previous works showed that this flow presents more similarities with a mixing-layer flow than with the standard boundary-layer flow. In this paper, this problem was studied for homogeneous canopies, using large eddy simulation (LES). The numerical results reproduced correctly the various steps of development of this flow: the appearance of a first generation of coherent structures resulting from the development of a primary Kelvin-Helmholtz instability, the reorganization of these structures, by vortex pairing and kinking, the development of a secondary instability and the formation of horseshoe vortices. Then, the process of transport of a passive scalar from a forest canopy into a clear atmosphere was studied in two cases, i.e., when the passive scalar concentration at the surface foliage is either constant or time-varying. Even though this small difference has little influence on the concentration patterns, the results showed that it can significantly affect the concentration magnitude as well as the dynamics of the total concentration in the atmosphere.
K. Gavrilov, Dominique Morvan, Gilbert Accary, Dimitry Lyubimov, Sofiane Meradji. Numerical simulation of coherent turbulent structures and of passive scalar dispersion in a canopy sub-layer. Computers and Fluids, 2013, LES of turbulence aeroacoustics and combustion, 78, pp.54-62. ⟨10.1016/j.compfluid.2012.08.021⟩. ⟨hal-01030794⟩
Dominique Morvan. Numerical study of the effect of fuel moisture content (FMC) upon the propagation of a surface fire on a flat terrain. Fire Safety Journal, 2013, 58, pp.121-131. ⟨10.1016/j.firesaf.2013.01.010⟩. ⟨hal-01030813⟩ Plus de détails...
This paper was devoted to clarify and evaluate how fuel moisture content (FMC) characterising a homogeneous vegetation layer (grass or shrubs), can affect the behaviour of surface fire. The approach used in this study was based on numerical simulations performed using a detailed fire physical model. The numerical results were analysed in terms of fire residence time, fire front depth, mass loss rate and rate of spread (ROS). Two windy conditions (calm and weak) were studied to evaluate the decay of the rate of spread (ROS) resulting from an increase of the fuel moisture content. The effect of wind velocity upon marginal burning conditions was also analysed. The numerical results were compared with empirical data of the literature.
Dominique Morvan. Numerical study of the effect of fuel moisture content (FMC) upon the propagation of a surface fire on a flat terrain. Fire Safety Journal, 2013, 58, pp.121-131. ⟨10.1016/j.firesaf.2013.01.010⟩. ⟨hal-01030813⟩
Konstantin Gavrilov, Dmitri Lyubimov, Dominique Morvan, Gilbert Accary, Sofiane Meradji. Admixture transport model for atmospheric boundary layer flow over forest canopy. N. I. Lobachevsky Bulletin de l'Université de Ninji-Novgorod, 1 (3), pp.244-252, 2013, La Modélisation Mathématique: Contôle Optimal. ⟨hal-01313312⟩ Plus de détails...
Konstantin Gavrilov, Dmitri Lyubimov, Dominique Morvan, Gilbert Accary, Sofiane Meradji. Admixture transport model for atmospheric boundary layer flow over forest canopy. N. I. Lobachevsky Bulletin de l'Université de Ninji-Novgorod, 1 (3), pp.244-252, 2013, La Modélisation Mathématique: Contôle Optimal. ⟨hal-01313312⟩
Dominique Morvan, Sofiane Meradji, William Mell. Interaction between head fire and backfire in grasslands. Fire Safety Journal, 2013, 58, pp.195-203. ⟨10.1016/j.firesaf.2013.01.027⟩. ⟨hal-01030810⟩ Plus de détails...
This paper deals with 3D numerical simulations of two fires fronts (head and backfire) propagating simultaneously through a grassland fuel. The simulations were carried out using a "fully" physical and three-dimensional fire model (namely WFDS). One of the objectives of this work, was to evaluate the potential for fully physical fire model to simulate the interactions between two fire fronts (a head fire and a backfire), in conditions similar to those encountered during suppression fire operations. A set of numerical simulations was first carried out for standalone head fires propagating through grasslands on a flat terrain and for various wind conditions ranging between 1 and 10 m/s. These results were compared with experimental data and numerical results from the literature. The same calculations were then repeated, with a backfire ignited at the downwind side of the plot. The numerical results highlighted that, for these particular conditions, head fire and backfire can interact, mainly, via two mechanisms: - at relatively large distances (greater than 10 m) the head fire acts on backfire as a screen and reduces the direct action of the wind flow on the backfire, - at relative small distances (nearly equal to 10 m) the gas flow (entrainment) generated in the vicinity of the head fire promotes the aspiration of the backfire towards the main fire front.
Dominique Morvan, Sofiane Meradji, William Mell. Interaction between head fire and backfire in grasslands. Fire Safety Journal, 2013, 58, pp.195-203. ⟨10.1016/j.firesaf.2013.01.027⟩. ⟨hal-01030810⟩
Dominique Morvan. Physical phenomena and length scales governing the behaviour of wildfires: a case for physical modelling. Fire Technology, 2011, 47 (2), pp.437-460. ⟨10.1007/s10694-010-0160-2⟩. ⟨hal-01022589⟩ Plus de détails...
This paper is an overview of the physical mechanisms and length scales governing the propagation of wildfires. One of the objectives is to identify the physical and mathematical constraints in the modelling of wildfires when using a "fully" physical approach. The literature highlights two regimes in the propagation of surface fires, i.e. wind-driven fires and plume-dominated fires, which are governed by radiation and convective heat transfer, respectively. This division leads to the identification of two governing length scales: the extinction length characterising the absorption of radiation by vegetation, and the integral turbulent length scale characterising the interaction between wind and canopy. Some numerical results published during the last decade using a fully physical approach are presented and discussed with a focus on the models FIRESTAR, FIRELES, FIRETEC and WFDS. Numerical simulations were compared with experimental data obtained at various scales, from laboratory to field fires in grassland and in Mediterranean shrubland. Some perspectives are presented concerning the potential coupling between physical fire models with mesoscale atmospheric models to study the impacts of wildfires at larger scale. Some of the topics on wildfire physical modelling that need further research are identified in the conclusions.
Dominique Morvan. Physical phenomena and length scales governing the behaviour of wildfires: a case for physical modelling. Fire Technology, 2011, 47 (2), pp.437-460. ⟨10.1007/s10694-010-0160-2⟩. ⟨hal-01022589⟩
K. Gavrilov, Dominique Morvan, Gilbert Accary, D.V. Lyubimov, Sofiane Meradji, et al.. Numerical modeling of coherent structures attendant on impurity propagation in the atmospheric boundary layer over a forest canopy. Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza, 2011, 46 (1), pp.138-147. ⟨10.1134/S0015462811010169⟩. ⟨hal-01030826⟩ Plus de détails...
Three-dimensional large eddy simulation is used to solve the problem for a homogeneous forest canopy. The development of the Kelvin-Helmholtz instability above the canopy leads to the formation of coherent structures in the atmosphere flow, which are reproduced in the calculations. The statistical characteristics of the flow obtained from the numerical modeling are compared with experimental data. The passive admixture transfer from the canopy to the clean atmosphere is studied for two cases, namely, for constant and variable coupled concentration of the impurity in the canopy.
K. Gavrilov, Dominique Morvan, Gilbert Accary, D.V. Lyubimov, Sofiane Meradji, et al.. Numerical modeling of coherent structures attendant on impurity propagation in the atmospheric boundary layer over a forest canopy. Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza, 2011, 46 (1), pp.138-147. ⟨10.1134/S0015462811010169⟩. ⟨hal-01030826⟩
Journal: Fluid Dynamics / Izvestiya Akademii Nauk - Mekhanika Zhidkosti i Gaza
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Sofiane Meradji, et al.. Numerical simulation of coherent structures over plant canopy. Flow, Turbulence and Combustion, 2011, 86 (1), pp.89-111. ⟨10.1007/s10494-010-9294-z⟩. ⟨hal-01022574⟩ Plus de détails...
This paper reports large eddy simulations of the interaction between an atmospheric boundary layer and a canopy (representing a forest cover). The problem is studied for a homogeneous configuration representing the situation encountered above a continuous forest cover, as well as for a heterogeneous configuration representing the situation similar to an edge or a clearing in a forest. The numerical results reproduces correctly all the main characteristics of this flow as reported in the literature: the formation of a first generation of coherent structures aligned transversally with the wind flow direction, the reorganization and the deformation of these vortex tubes into horse-shoe structures. The results obtained when introducing a discontinuity in the canopy (reproducing a clearing or a fuel break in a forest), are compared with the experimental data collected in a wind tunnel; here, the results confirm the existence of a strong turbulence activity inside the canopy at a distance equal to 8 times the height of the canopy, referenced in the literature as the Enhance Gust Zone (EGZ) characterized by a local peak of the skewness factor.
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Sofiane Meradji, et al.. Numerical simulation of coherent structures over plant canopy. Flow, Turbulence and Combustion, 2011, 86 (1), pp.89-111. ⟨10.1007/s10494-010-9294-z⟩. ⟨hal-01022574⟩
Dominique Morvan, Chad Hoffman, Francisco Rega, William Mell. Numerical simulation of the interaction between two fire fronts in grassland and shrubland. Fire Safety Journal, 2011, 46 (8), pp.469-479. ⟨10.1016/j.firesaf.2011.07.008⟩. ⟨hal-01022562⟩ Plus de détails...
The objective of this paper was to evaluate the potential for fully physical fire models to simulate the interactions between two converging fire fronts (a head fire and a back fire), in conditions similar to those encountered during suppression fire operations. The simulations were carried out using two fully physical models: FIRESTAR, in two dimensions, and Wildland Fire Dynamics Simulator, in three dimensions. Each modelling approach numerically solves a set of balance equations (mass, momentum, energy, etc.) governing the behaviour of the coupled system formed by the vegetation and the surrounding atmosphere. Two fuel profiles were tested: homogeneous grassland similar to landscapes in Australia and a shrubland representative of Mediterranean landscape (garrigue). Results from the two-dimensional and three-dimensional simulations were used to investigate how the two fire fronts interact together and mutually modify, or not, their own behaviour before merging. The results of these simulations showed that the merging of two fire fronts can result in a quick increase in fire-line intensity or in flame height. We concluded that physics-based simulations do reproduce reasonable and expected head- and back-fire interactions, but more work is needed to further understand the accuracy of such predictions.
Dominique Morvan, Chad Hoffman, Francisco Rega, William Mell. Numerical simulation of the interaction between two fire fronts in grassland and shrubland. Fire Safety Journal, 2011, 46 (8), pp.469-479. ⟨10.1016/j.firesaf.2011.07.008⟩. ⟨hal-01022562⟩
Дмитрий Викторович Любимов, Константин Алексеевич Гаврилов, Dominique Morvan, Gilbert Accary, Sofiane Meradji, et al.. Численное моделирование когерентных структур при распростра-нении примеси в атмосферном пограничном слое над лесным пологом. Вычислительная механика сплошных сред, 2010, 3 (2), pp.34--45. ⟨hal-01291552⟩ Plus de détails...
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Oleg A Bessonov, et al.. Large eddy simulation of coherent structures over forest canopy. Deville M.; Lê T-H.; Sagaut P. Turbulence and Interactions: Proceedings the TI 2009 conference, Springer, pp.143-149, 2010, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 9783642141386. ⟨10.1007/978-3-642-14139-3_17⟩. ⟨hal-01024672⟩ Plus de détails...
This paper deals with the numerical simulation (using a LES approach) of the interaction between an atmospheric boundary layer (ABL) and a canopy, representing a forest cover. This problem was studied for a homogeneous configuration representing the situation encountered above a continuous forest cover, and a heterogeneous configuration representing the situation similar to an edge or a clearing in a forest. The numerical results, reproduced correctly all the main characteristics of this flow, as reported in the literature: the formation of a first generation of coherent structures aligned transversally from the wind flow direction, the reorganisation and the deformation of these vortex tubes to horse shoe structures. The results obtained, introducing a discontinuity in the canopy (reproducing a clearing or a fuel break in a forest), were compared with experimental data collected in a wind tunnel. The results confirmed the existence of a strong turbulence activity inside the canopy at a distance equal to 8 times the height of the canopy, referenced in the literature as an Enhance Gust Zone (EGZ) characterized by a local peak of the skewness factor.
Konstantin Gavrilov, Gilbert Accary, Dominique Morvan, Dimitry Lyubimov, Oleg A Bessonov, et al.. Large eddy simulation of coherent structures over forest canopy. Deville M.; Lê T-H.; Sagaut P. Turbulence and Interactions: Proceedings the TI 2009 conference, Springer, pp.143-149, 2010, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 9783642141386. ⟨10.1007/978-3-642-14139-3_17⟩. ⟨hal-01024672⟩
D Morvan, Sofiane Meradji, G Accary. Physical modelling of fire spread in grasslands. Fire Safety Journal, 2009, 44 (1), pp.50--61. ⟨hal-01291553⟩ Plus de détails...
D Morvan, Sofiane Meradji, G Accary. Wildfire behavior study in a Mediterranean pine stand using a physically based model. Combustion Science and Technology, 2007, 180 (2), pp.230--248. ⟨hal-01291554⟩ Plus de détails...
D Morvan, Sofiane Meradji, G Accary. Wildfire behavior study in a Mediterranean pine stand using a physically based model. Combustion Science and Technology, 2007, 180 (2), pp.230--248. ⟨hal-01291554⟩
E. Rigolot, D. Morvan. Evaluation de l'efficacité des coupures de combustible par deux approches : dires d'experts et modélisation. Forêt Méditerranéenne, 2003, XXIV (4), pp.403-418. ⟨hal-03564541⟩ Plus de détails...
Cette étude vise à identifier les principes de conception des coupures de combustible qui favorisent leur efficacité et à déterminer les seuils opérationnels pour les principaux paramètres retenus. Deux approches ont été utilisées : par modélisation et à dires d'experts. L'analyse statistique multivariée révèle que les critères les plus discriminants pour l'évaluation de l'efficacité d'une coupure de combustible sont : la largeur, le volume de broussaille et le recouvrement des arbres. Des modèles logistiques ont pu être ajustés pour prédire la probabilité d'arrêt du feu en fonction des caractéristiques des coupures.
E. Rigolot, D. Morvan. Evaluation de l'efficacité des coupures de combustible par deux approches : dires d'experts et modélisation. Forêt Méditerranéenne, 2003, XXIV (4), pp.403-418. ⟨hal-03564541⟩
