关键词: 旋翼, 地面效应, 流场显示, 下洗流, 流速测量

Abstract:

Results of an experimental study of the aerodynamics of a helicopter rotor in ground effect at low speeds are presented in this paper. Experiments of rotor wake flow visualization and induced velocity measurement near the rotor disc were conducted. At some advance rotio, the forward part of the rotor wake, after impinging on the ground, rolls up and recirculates near the rotor leading edge and large increase in induced velocity appears near the rotor leading edge. When the advance ratio increases, the rolled-up wake develops into concentrated vortex, ground vortex, under the rotor and the induced velocity near the rotor leading edge becomes much smaller.The ground vortex diminishes as the advance ratio further increases. Recirculation and ground vortex occur in a very nerrow region of the advance ratio. These results explain the irregular variations of rotor forces and moments with advance ratio reported in previous works.

Key words: rotors, ground effects, flow visualization, down wash flow, flow velocity measurement