The role of helicity and fire–atmosphere turbulent energy transport in potential wildfire behaviour

Abstract

Background. Understanding near-surface fire–atmosphere interactions at turbulence scale is fundamental for predicting fire spread behaviour. Aims. This study aims to investigate the fire–atmosphere interaction and the accompanying energy transport processes within the convective boundary layer. Methods. Three groups of large eddy simulations representing common ranges of convective boundary layer conditions and fire intensities were used to examine how ambient buoyancy-induced atmospheric turbulence impacts fire region energy transport. Key results. In a relatively weak convective boundary layer, the fire-induced buoyancy force could impose substantial changes to the near-surface atmospheric turbulence and cause an anticorrelation of the helicity between the ambient atmosphere and the fire-induced flow. Fire-induced impact became much smaller in a stronger convective environment, with ambient atmospheric flow maintaining coherent structures across the fire heating region. A highefficiency heat transport zone above the fire line was found in all fire cases. The work also found counter-gradient transport zones of both momentum and heat in fire cases in the weak convective boundary layer group. Conclusions. We conclude that fire region energy transport can be affected by convective boundary layer conditions. Implications. Ambient atmospheric turbulence can impact fire behaviour through the energy transport process. The counter-gradient transport might also indicate the existence of strong buoyancy-induced mixing processes.