Abstract: Helicopter brownout blocks out pilots’ sight, leads to difficulty in landing and nap-of-the-earth flight, and induces flight accidents. A sand particle Discrete Element Method (DEM) model based on discrete dynamics and a sand particle-flow interaction model are established and coupled with the rotor viscous vortex particle model and viscous ground aerodynamic model to account for translation and collision of sand particles under the effect of the rotor flow field, and an analysis method of helicopter brownout is then proposed to analyze the characteristics of helicopter brownout. The flight test of EH-60L brownout in the US Army Yuma Proving Ground is used for comparison. It is shown that the predicted shape, position and height of uplift, process of the sand cloud are consistent with those of the flight test. Compared with the Lagrangian dust cloud simulation based on splash entrainment, process of bombardment, particle flux and threshold velocity with assumption, the predicted profile of the sand cloud is more accurate, and in better agreement with the flight test result. Then, the processes of helicopter brownout in hover and forward flight are investigated. Results show that the wall jet induced by the rotor tip-vortex and ground interaction yields translation and sediment trapping of sand, producing bombardment ejection and saltation. Uplift of sediment induced by the flowfield generates dust cloud, and covers the front view of the helicopter, thus forming brownout.

Key words: brownout, sand particles, DEM, viscous vortex particles, rotors