Modeling the propagation of a wildfire through a Mediterranean shrub using a multiphase formulation

The propagation of wildfire through a Mediterranean shrub has been numerically simulated using a multiphase formulation. This approach was based on a complete description of the physical phenomena contributing to the propagation of a surface fire through a solid fuel layer. The heterogeneous character of the vegetation (nature, foliage, twigs, trunk, etc.) was taken into account using families of solid particles, which are characterized by specific physical properties such as the surface area/volume ratio, the moisture content, the density, and the volume fraction. Using this approach, the interaction between dead and living fuel, which plays a significant role in the propagation of a wildfire, was taken into account. The evolution of the state of each solid fuel family was computed by solving the mass and energy balances, including the effects of thermal degradation of the vegetation (drying, pyrolysis, and glowing combustion) and the exchanges of mass, momentum, and energy with the surrounding gas. The calculations were performed for a surface fire propagating through Mediterranean vegetation composed of shrubs (Quercus coccifera) and grasses (Brachypodium ramosum). The results show the effects of wind on heat transfer between the fire front and the vegetation. Two modes of fire propagation are identified: plume-dominated fires and wind-driven fires, respectively dominated by radiation and convection heat transfer.