The role of the terrain-modified wind on driving the fire behaviour over hills: an Experimental and Numerical Analysis

Abstract

This paper analyses the fire behaviour over two hills placed in series in the direction of the wind. Laboratory-scale experiments under various slope and wind velocity conditions with changing the distance between the hills revealed two sorts of extreme fire behaviour that might take place. One is a lateral fire spread over the lee slopes (fire channelling), and the other is an eruptive fire behaviour (blow-up) happens over the windward face of the secondly ordered hill in the direction of the wind. The changes in the blowing wind velocity and the distance between the hills were found to have a significant effect on fire behaviours, where increasing the wind speed or the distance resulted in a faster rate of spread of the fire. Also, the change of the ignition point, or spreading direction of the fire relatively to the wind direction has a significant effect on the fire channelling behaviour where it was found that the fire channelling is more extreme if the fire is spreading against the main wind direction. Numerical analysis of the adiabatic flow field showed that the change the presence of these extreme fire behaviour is related directly to the terrain-modified flow topology. The interactions between the terrain-modified wind mechanisms and the fire result in accelerated flows that drive the indicated extreme fire behaviours.