Simulations of surface fire propagating under a canopy: flame angle and intermittency

Abstract

We conduct physics-based simulations of a wind driven surface fire entering, propagating through, and leaving a region of aerodynamic drag. This is an idealised model of a real-world grassfire propagating through a short canopy such as a stand of trees. The study is motivated by the need to understand how fires entering forested regions adjust to the lower wind speed inside the forest. This will lead to more informed operational modelling practices and predictions of fire spread. In these simulations the driving open (10 m) wind speed is varied from 1 ms-1 to 10 ms-1. For lower driving wind speeds the rate-of-spread of the fire is largely unaffected by the canopy, however, for the higher driving wind speeds the fire appears to transition from a wind-driven mode, characterised by a low flame angle to a buoyancy-driven mode, characterised by a nearly vertical flame.