Measurements of Rotor/Airframe Interactions in Ground Effect Over a Sediment Bed

摘要

Time-resolved particle image velocimetry and particle tracking velocimetry measurements were madernin the flow below a rotor that was hovering over a ground plane covered with a mobile sediment bed.rnThe experiments were performed with an isolated rotor and with three different bodies placed in thernrotor wake near the ground. The goal was to better understand of the interactions of the rotor wakernwith the body, and to examine how such interactions may influence the mobilization and uplift ofrnparticles from the bed. Single-phase and dual-phase flow measurements were taken over vertical andrnhorizontal planes near the nose and tail regions of the body, as well as near to the ground plane.rnThe results showed that the flow over the nose of the bodies was similar to the isolated rotor, thoughrnsome mild interactions occurred between the blade tip vortices and the surface boundary layers onrnthe bodies. The wake interacted strongly with the tail of each body, the resulting flow at the groundrnalso being significantly affected. In the cases where there was direct impingement of the tip vorticesrnon the body, the vortex developed into a loop, followed by stretching and thinning of the core, andrnfinally bursting as the flow detached from the surface. The dual-phase results showed that with thernbodies present, sediment particles were suspended radially closer to the rotor. The three-dimensionalrnvariations in the flow below the tail of each body also resulted in significantly different distributions ofrnparticles being suspended.