Numerical study on helicopter brownout with crosswind

In previous studies, helicopter brownout was investigated using various numerical methods, but the influence of a crosswind on the evolution of the dust cloud was not considered. In the present study, a method for analyzing helicopter brownout is developed that includes the effects of a crosswind on the unsteady flow field and the dynamics of the sand particles. The evolution of the dust cloud is simulated and compared with flight-test data obtained with no crosswind, and the differences in the dust clouds with and without a crosswind are investigated. Also, the influences of crosswind direction and velocity on the behavior of the dust cloud are analyzed. The results show that a crosswind has significant influence on the behavior of the dust cloud. A crosswind from the port side strengthens the dust cloud greatly, whereas a headwind weakens it. Compared with that when the crosswind is from the starboard side, the density of the dust cloud when the crosswind is from the port side is greater because the interaction between the crosswind and the rolled-up vortex on the retreating side is stronger than that on the advancing side. When the crosswind is from the port side, the density of the dust cloud increases initially and then decreases with increasing crosswind velocity.