Fire against Fire: Computational Modelling of Wildfire In-Draft Flows for Suppression by Counter Firing

Devastating wildfires are reported every year all over the globe and their safety impact can be substantial. Efficient firefighting techniques are therefore desired as one way to limit the damage they can cause. Sometimes, a wildfire is too big to be fought directly and one of the few solutions available is to deprive it of fuel. This is done by using fire-breaks: strip of land without any fuel to burn. This paper focuses on a fire suppression method called counter-firing which uses fire to fight fire. The method consists in creating a fire-break by igniting a second fire ahead of the wildfire. This technique, despite being hazardous, can be very effective. Unfortunately, its mechanisms are not understood as very little research has been done on the subject. The aim of this paper is to use Computational Fluid Dynamics (CFD) and a 2D model to simulate the velocity field around a wildfire, putting emphasis on the in-draft flow. The in-draft is a buoyancy driven flow that pulls fresh air from the surroundings towards the wildfire. It can be very helpful to handle the counterfiring process as it can move against the main wind direction and therefore drive the counter-fire towards the wildfire. The problem considered is a wildfire in an open land subject to a cross wind. The domain is 2D, the equations are solved using the Unsteady Reynolds Averages Navier-Stokes Equations (URANS) with the k-e turbulence model. The simulations gave a general shape of the in-draft flow with distance to the wildfire as well as the influence of the wind velocity and the intensity of the fire. The model was able to predict some general results in agreement with previous studies. It also showed some non-physical flow behavior that can be explained by the dimensionnality of the domain. This is the main conclusion of the present study: a wildfire in the cross wind cannot be modeled in 2D but 3D is required