Experimental Study of Aerodynamics and Wingtip Vortex of a Rectangular Wing in Flat Ground Effect

Abstract

The ground effect on the aerodynamics and tip vortex flow of a rectangular wing is investigated experimentally at Re = 2.71 × 105. The results show that there is a large lift increase with reducing ground distance. By contrast, only a small drag increase is observed in ground effect except in close ground proximity for which a great drag increase appears. The tip vortex also moves further outboard and upward with reducing ground distance. Near the ground, there is the presence of a corotating ground vortex (produced by the rolling up of the boundary layer developed on the ground surface), leading to an increased vortex strength. In extreme ground proximity, a counterrotating secondary vortex (SV) (induced by the crossflow of the tip vortex), relative to the tip vortex, appears which causes a reduced vortex strength and a lowered lift-induced drag, as well as a vortex rebound. The impact of ground effect on the vortex flow properties is also discussed. The lift-induced drag, computed based on the crossflow measurements via the Maskell wake integral method, in ground effect is also compared against the inviscid-flow predictions and wind tunnel total drag force measurements.