Insight into laboratory-scale junction-fire dynamics using 3-D physics-based numerical simulations

Abstract

Junction fires exhibit complex behaviour and are characterised by unique physical processes, which have attracted considerable interest in the wildfire community. This paper provides an in-depth analysis of junction-fire dynamics, leveraging numerical simulations to understand the mechanisms responsible for fire-spread deceleration observed experimentally and to provide insights about the characteristics of fire-induced wind. Using the FIRESTAR3D model, a fully physical, CFD, wildfire simulator, junction fire simulations were conducted at laboratory scale under various junction angles, terrain slopes, and prescribed wind speeds. An analysis of the interaction between the flow field and the flames’ structure was carried out. Results show that the deceleration phase of junction fire propagation, observed experimentally at small junction angles on a horizontal terrain with no imposed wind, is due to a change in the flame direction preceding the fire-spread deceleration, resulting in a decrease in the interaction between the arms of the junction fire. The study also provides a better understanding of the action of fire-induced wind and competition with the prevailing wind in shaping the junction fire flames. This study offers new insights into the complex dynamics of junction fires, and the analysis of induced wind supports the development of comprehensive scaling laws for their behaviour.