Research

Physics-based Simulation of Extreme Wildfire Behavior on Sloping Terrain

Project Details

Abstract

This work delves into the complexities of wildfire behavior on sloping terrain, where the combined effect of crosswind and slope acting in the same direction substantially influence fire behavior, rate of spread, and fire intensity. Fire regime depends on Byram’s convective number that was modified to account for slope effect (Morvan and Accary 2024), For steep slopes, this correction results in a convective number that is significantly different from the formulation proposed by Nelson (2015). To test the effectiveness of the proposed Byram’s number expression, Large Eddy Simulations of shrubland fires were carried out using a 3D fully-physical CFD fire simulator (FireStar3D) under various terrain slopes and prevailing crosswind speeds, covering both wind-dominated fire regime and plume-dominated one. Results showed that the proposed modification of Byram’s convective number allows a better description of the obtained fire regime. The heat transfer mechanisms governing fire propagation were described, highlighting in particular the role played by the convective cooling of unburnt vegetation in the case of a plume-dominated fire as the fire draws an adverse air flow in the opposite direction of fire propagation.

Temperature field and streamlines
Temperature field and streamlines obtained in the vertical median plane of a plume-dominated fire, 90 s after ignition, in the case of 10° slope, an initial crosswind speed of 0.5 m/s, and quasi-infinite fire front. Earth-gravity direction is indicated by an arrow.