A Multidimensional Model for Simulating Vegetation Fire Spread using a Porous Media Sub-model

摘要

An unsteady multidimensional model is reported with the objective of studying wildfires. The present work aims to validate the modelling assumptions against rcported experiments of a lab-scale line fire through a vegetation fuel bed. In this model the foel bed is assumed to be a porous medium with a raudomly orientated discrete solid matrix. A set of time dependent equations of mass, momentum, species and energy are obtained for the gas and solid phase. The hydrodynamic turbulence model is based on a k-εeddy viscosity model extended to buoyancy effects and to flow through vegetation. The effects of devolatilization of cellulose material, comhustion of gas and heat transfer between gas and solid matrix are simulated. The radiative heat transfer equation in the foel bed is solved using the discrete ordinates method developed for a porous medium. Soot formation and its impact on radiation are accounted for. The solution is performed numerically by a finite volume method. This model has been applied for the prediction of fire spreading through a litter of pine needles. The predicted rates of fire spread and fuel mass consumption for two cross wind velocities are presented and compared with measurements showing a satisfactory agreement.