Aerodynamics of an aerofoil in transonic ground effect: Methods for blowdown windtunnel scale testing

Abstract

Abstract Experimental aerodynamic testing of objects in close ground proximity at high subsonic Mach numbers is difficult due to the construction of a transonic moving ground being largely unfeasible. Two simple, passive methods have been evaluated for their suitability for such testing in a small blowdown wind tunnel: an elevated ground plane, and a symmetry (or mirror-image) approach. The methods were examined using an unswept wing of RAE2822 section, with experiments and Reynolds-Averaged Navier Stokes CFD used synergistically to determine the relative merits of the techniques. The symmetry method was found to be a superior approximation of a moving ground in all cases, with mild discrepancies observed only at the lowest ground clearance. The elevated ground plane was generally found to influence the oncoming flow and distort the flowfield between the wing and ground, such that the method provided a less-satisfactory match to moving ground simulations compared to the symmetry technique.