INFLUENCE OF WATER BARRIER ON DYNAMICS OF THE FOREST FIRE DEPENDING ON TERRAIN

This work deals with modeling fire extinguishing based on physical model. The water barrier can be formed by wetting forest materials. Unlike the moisture present in the wood there is free water have. Its boiling point is considered a constant in this study. During the practical calculation it is assumed that in each cell having a temperature above 373 K and a nonzero fraction of free water, boiling takes place. Its rate is determined by minimum between the amount of free water that exists in the cell and the amount of energy which is sufficient to boil water. To determine the critical value of the fraction of the water needed to prevent further spread of the fire, we used the method of dichotomy. It was assumed that there exists a critical value wb cr ,such that the fire overcomes the barrier for any value wb < wb cr and extinguishes at wb > wb cr . wb cr = 0 means that fire can't propagate under present conditions even in the absence of the barrier. To check whether the fire was successfully extinguished by the barrier uses two key criteria: the maximum temperature inside the canopy and the mass fraction of dry organic substance near the right boundary of the computational domain. Executed calculations have shown that the required fraction of water in the barrier is minimal at suppression a fire on the plain (wb cr = 0.785). When extinguishing a fire on the plateau of the hill — it takes much more water due to greater intensity of the fire (wb cr = 1.235). Fire extinguishing at the bottom of the ravine requires even much more water (wb cr = 3.485) due to the formation of vortices and the large tilt angle of the flame.