Numerical study of a crown fire spreading toward a fuel break using a multiphase physical model.

摘要

The propagation of a wildfire through a Mediterranean pine stand was simulated using a multiphase physical model of fire behaviour. The understorey was composed of a mixture of shrub (Quercus coccifera, Brachypodium ramosum) and the canopy was composed of pine crowns (Pinus halepensis). The heterogeneous character of the vegetation was taken into account using families of solid particles, i.e. the solid phases (foliage, twigs, grass). The thermal decomposition of the solid fuel by drying and pyrolysis, and the combustion of chars were considered, as well as the radiative and convective heat transfer between the gas and the vegetation. In the gaseous phase, turbulence was modelled using a two transport equations model (RNG k- epsilon ) and the rate of combustion, which was assumed to be controlled by the turbulent mixing of fuel and oxygen, was calculated using an eddy dissipation concept. The radiation transfer equation, which includes absorption and emission of both the gas-soot mixture and the vegetation, was solved to calculate the contribution of radiation to the energy balance equations. Numerical solutions were calculated in a two-dimensional domain (vertical plane). Results showed the ability of this approach to simulate the propagation of a crown fire and to test the efficiency of a fuel break with success. The effects of the terrain slope were also tested. Some effects on fire behaviour of vortices resulting from the interaction of the wind flow with the canopy layer are shown..