Physics-based modelling of wind-driven junction fires

Abstract

Numerical simulations of laboratory-scale junction fires were performed for a shrub fuel bed, using the fully-physical model FIRESTAR3D under various unidirectional wind conditions on different terrain slopes and junction angles. Simulations were carried out for a junction angle ranging from 15° to 90°, for a slope angle varying between 0 and 40°, and for low to intermediate driving wind speed, ranging from 0 to 4 m/s. Simulations show surge-and-stall-like behaviour of fire spread that is irregularly enhanced by the action of wind. Results of fire spread show that the effect of the junction angle on fire behaviour is non-linear, becoming stronger as the angle decreases. Both wind and slope effects are concealed by the junction effect for small angles, while wind has a significant impact at intermediate values of the junction angle. The driving heat transfer mode in junction fires varies based on the slope condition: on sloping terrain, convection is dominant for any wind speed, while on non-sloping terrain, radiation is the driving mode in no-wind condition but convection plays the greater role as the wind speed increases.