Reduction of a multiphase formulation to include a simplified flow in a semi-physical model of fire spread across a fuel bed

The aim of our ongoing research is to propose a forest fire simulator. To this end, we have developed a semi-physical model of fire spread that has been validated experimentally thanks to laboratory-scale pine needle bed fires under both slope and low wind conditions. This model described the physical phenomena in a simple manner while providing the main characteristics of spread. However, it did not allow to describe accurately the experimental tendency of an increasing spread rate with increasing wind velocity, particularly because of the strong assumption of considering a constant wind over the entire spreading zone. In the present study, we propose a simplified description of the flow that is coupled to our model. To proceed, we carry out the reduction of a multiphase model of reference. This reduction of the complete equations that describe the flow allows us to develop a simplified flow by considering mainly the buoyancy effect induced by combustion in the flaming zone. The results are subsequently compared to laboratory experiments under varying wind and slope conditions. A substantial improvement of the predicted rates of spread is provided. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.