The roles of two physical effects in wildfire are explored through simulations in this study. They are the spatial variation of the bulk density of crown fuel and the thermophoresis forces acting on the produced soot particles. The spatial variation of crown fuel bulk density is modeled as a function of shrub height. This function is available from experimental measurements carried out on Chamise, as crown fuel, in a previous study. In the current study, it is shown that flame spread rate and crown fire initiation are two global parameters considerably affected when the spatial variation of the bulk density is taken into account. Also, it is indicated that thermophoresis forces on soot particles have a significant impact on the evolution of solid- and gas-phase temperature in the upper region of crown fuel; however, other fire propagation characteristics are not considerably affected by these forces. In the simulations, turbulence is modeled with the large eddy simulation and radiation is modeled with the discrete ordinate method. Mass, momentum, and energy transfer between gas and solid-fuel phases are modeled through coupling terms.

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