Physique et modélisation du comportement des feux de forêt (thèse 2015 - 2019)
Publications scientifiques au M2P2
Nicolas Frangieh, Dominique Morvan, Sofiane Meradji, G. Accary, O. Bessonov. Numerical simulation of grassland fires behavior using an implicit physical multiphase model. Fire Safety Journal, Elsevier, 2018, 102, pp.37-47. 〈hal-01978037〉 Plus de détails...
This study reports 3D numerical simulations of the ignition and the propagation of grassland fires. The mathematical model is based on a multiphase formulation and on a homogenization approach that consists in averaging the conservation equations (mass, momentum, energy …) governing the evolution of variables representing the state of the vegetation/atmosphere system, inside a control volume containing both the solid-vegetation phase and the surrounding gaseous phase. This preliminary operation results in the introduction of source/sink additional terms representing the interaction between the gaseous phase and the solid-fuel particles. This study was conducted at large scale in grassland because it represents the scale at which the behavior of the fire front presents most similarities with full scale wildfires and also because of the existence of a large number of relatively well controlled experiments performed in Australia and in the United States. The simulations were performed for a tall grass, on a flat terrain, and for six values of the 10-m open wind speed ranged between 1 and 12 m/s. The results are in fairly good agreement with experimental data, with the predictions of operational empirical and semi-empirical models, such as the McArthur model (MK5) in Australia and the Rothermel model (BEHAVE) in USA, as well as with the predictions of other fully 3D physical fire models (FIRETEC and WFDS). The comparison with the literature was mainly based on the estimation of the rate of fire spread (ROS) and of the fire intensity, as well as on the analysis of the fire-front shape.
Nicolas Frangieh, Dominique Morvan, Sofiane Meradji, G. Accary, O. Bessonov. Numerical simulation of grassland fires behavior using an implicit physical multiphase model. Fire Safety Journal, Elsevier, 2018, 102, pp.37-47. 〈hal-01978037〉
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, Elsevier, 2018, 101, pp.39-52. 〈hal-01946956〉 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, Elsevier, 2018, 101, pp.39-52. 〈hal-01946956〉
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, CSIRO Publishing, 2018, 27 (9), pp.636-641. 〈hal-01947197〉 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, CSIRO Publishing, 2018, 27 (9), pp.636-641. 〈hal-01947197〉