Advances on helicopter brownout

The interference of the helicopter rotor and the ground causes the lifting of dust, which leads to the phenomenon of brownout. The phenomenon threatens the flight safety of helicopter seriously, and therefore, it is necessary to carry out relevant researches on the aerodynamic basis for the brownout. In this paper, the research progress of helicopter brownout is deeply analyzed from four aspects: numerical methods, experimental techniques, formation mechanism, and suppression methods. Investigations demonstrate that the coupled vortex method or CFD method and the Lagrange sand tracking method can realize simulations of the sand cloud profile and the phenomenon of brownout, but the key factors such as the complex sand bed surface, fluctuating turbulence, migration of sand particles, aggregation, and lifting of sand particles need to be concentrated on. The brownout experimental system built with high-speed PIV techniques and high-speed camera can obtain the morphology data of the sand cloud, but it is still necessary to study the simulation methods of the complex sand bed and the measurement techniques of dust spatial concentration, to explore the driving mechanism of sand particles and the evolution mechanism of brownout, and to develop the design methods and technical approaches to effectively weaken brownout.