Forest fire propagation has been studied intensively during the past several decades. The driving mechanism for fire propagation is the transfer of the heat released from the fuel combustion, through a combination of diffusion, convection and radiation. Convection is highly dependent on the forced and buoyancy-driven turbulent transport. It is a self-determined process due to the coupling of chemical reactions, fluid flow and heat transfer. Atmospheric and geographic conditions, fuel structure, and fuel type are all among the important factors affecting the fire spread behavior.

In this talk, we examine the effects of vegetation drag and fuel type on fire spread using a physics-based model for a 160m×160m×615m domain. A thin layer of solid fuel is distributed uniformly on the bottom surface. One solid-phase reaction is considered, for which the rate is determined by the temperature and by the availability of fuel and oxygen. The gas phase is described by the equations for fully compressible flow, and turbulence is represented by a two-equation model for turbulent kinetic energy and dissipation based on the renormalization group method (so-called RNG k - E model). A drag force is applied in the fuel layer to represent the effect of drag due to vegetation. In an attempt to represent different fuel types, the amount of heat released from unit fuel combustion is varied. The current model may be considered somewhat crude given the simplified models for combustion and turbulence, and the neglect of radiation; nevertheless, the goal of this study is to examine the dependence of the spread rate and combustion intensity on the vegetation drag and fuel type. Results will be shown from simulations in which the drag and fuel type are varied systematically. Additional simulations using laminar diffusion also will be shown that assess the importance of the turbulence model on the spread rate.