A Numerical Study of Water Dump in Aerial Fire Fighting

In large forest fires over wide areas, aerial fire fighting with water dumping from helicopters and aircrafts has been widely employed in the world, but water dropped from helicopters is not always sufficient to control large fires, since the limited quantity of water that can be carried aloft is a critical issue and also, the duration of aerial fire fighting is necessarily limited to daytime operations. On the other hand, aircrafts can drop large amounts of water, but the aircrafts flying at high-speed and low altitudes are dangerous due to tall buildings, trees and electric power lines. Therefore, aircrafts tend to fly at high altitudes, where the dropping water spreads out as mists in the air. As a result, accurate engineering data on the water supply relative to given fires are critically needed to design the fire-fighting strategies. The objective of this study is to examine the optimum strategies to apply water by the aerial fire fighting. However, tests by real aircrafts to obtain such information would be too costly. Therefore, the patterns of water dumping from aircrafts as well as from helicopters were examined in a first-attempt CFD simulation, together with the investigation of the data in previous real aerial fire fighting tests. It has been found in the CFD simulations that the patterns of dropping water in the air and the corresponding water density on the ground give reasonable results compared to those from the real aerial tests.