Ground Effect of a Rotor Hovering above a Confined Area

In this study, an experimental investigation of the effects of confined area geometry on the aerodynamic performance of a hovering rotor has been carried out from a standpoint of flight safety. The confined area is simulated by placing vertically a single plate or a couple of parallel plates on the ground effect plate. The aerodynamic performance of the rotor changes because a part of the rotor wake upward along the walls interferes with the flow field around the rotor. It is shown that the behavior of the steady and vibratory torque coefficients of the rotor remarkably depends on the combinations of the space between walls, the wall height, and the rotor height from the ground plate. The required torque coefficient in the presence of walls increases at all in-ground-effect rotor heights when compared with that without walls and can exceed the maximum usable out-of-ground-effect rotor power coefficient.