关键词: 沙盲, 直升机, 旋翼近地干扰, 数值模拟, 机理

Abstract: When helicopters fly near loose surfaces such as deserts and Gobi terrain, the complex interference flow field formed between the rotor and the ground induces the movement of sand bed particles, easily leading to the brownout phenomenon that obscures the pilot's vision and threatens flight safety. Based on a CFD/DEM coupled numerical analysis method for helicopter brownout, this paper deeply investigates the formation mechanism of brownout driven by the rotor/ground interference flow field from the perspective of “flow structure-particle transport”. The research results indicate that the brownout phenomenon is essentially a continuous process of particle initiation, outward migration, lifting, and suspension under the combined action of the rotor downwash, ground wall jet, and tip vortices. The rotor downwash provides the initial kinetic energy for particle initiation, the ground wall jet dominates the near-ground radial transport of particles, and the tip vortices control the lifting and spatial diffusion of outer particles. The spatiotemporal asynchronous evolution of successive tip vortices creates a significant cumulative effect, enhancing localized particle transport and suspension. Particle diameter has a distinct impact on brownout evolution; larger particles are prone to settling and deposition due to gravity, while smaller particles maintain suspension more easily. Rotor flow field structures, such as the downwash, all have clearly defined dominant interaction zones: 0.8~1.4R is the downwash impingement zone, where the average particle concentration decreases by 99.10% within the flow interaction time; 1.4~2.0R is the ground wall jet displacement zone, where the average particle concentration decreases by 99.03% within the flow interaction time; and the area beyond 2.0R is the zone dominated by tip vortex entrainment.

Key words: brownout, helicopter, rotor in-ground interference, numerical simulation, mechanism