Dust entrained by low flying helicopters leads to the degraded visual environment, brownout. Particle inception is a critical stage in the development of the dust cloud. Here, near-wall Lagrangian particle forces are considered through analyzing an approximate time-averaged full-scale rotor flow.This simplified flow does not attempt to predict brownout, instead it provides scales and velocity data in the near-wall region, compares the role of particle-fluid forces, and provides a foundation for Lagrangian entrainment models.The analysis shows that three characteristic particle sizes are exposed to different physics in different boundary layer zones, a function of the distance from the helicopter. Drag is the dominant aerodynamic force, cohesion is large for small particles, but wall-bounded lift is sufficient to entrainmedium-sized particles. A complementary analytical prediction of tip vortices found that both large-scale inviscid features and small-scale viscous features of the boundary layer are significant.
展开▼
