Cfd study of effect of water drop by aerial firefighting to protect forest fire growth

Abstract

Wildfires destroy the natural environment, cause property damages and cause victims, therefore great research effort is dedicated to improve protection against wildfires. As fire growth depends on many parameters to examine behavior relevant to fire protection methods systematically, we used CFD simulations to analyze the role of aerial fire-fighting. CFD simulations of the fire spread in relation to the water drop effect in aerial fire-fighting were done using the (15 x 15) fuel array in windy conditions. A single fuel cell is 8m x 8m x 2m, varying the space distance between the adjacent fuel cells. The water drop effect is examined as a function of the heat release rate, varying the wind speed. The results of our previous studies showed that it is difficult to extinguish the burning area in wildfires by directly dropping water over the flames and also it is less effective to drop water in the fringe areas of burning fires parallel to the wind direction. Therefore, the way selected in this study is to drop water in the downwind area slightly away from the fire front, making a water belt to reduce the radiative heat transfer. However, if the fuel distributes densely, even the water belt dropped in the area of 20m x 60m may not sufficient to stop the fire spread, since the fires may detour both sides of the water belt or the fires jump over the water belt. However, water dropped belts are very effective to delay the fire spreading speed. If the space distance between adjacent fuel cells is larger than 2m, the water belt can protect or highly delay the fire spread. One problem is the amount of water to realize such a water belt to stop the fire spread, since helicopters carry too few water and it is dangerous for helicopters to fly in the hot and smoky air. Large aircrafts carrying large amount of water are needed to make such a large water belt.