Compressible Dynamic Stall Performance of a Variable Droop Leading Edge Airfoil with a Gurney Flap

Abstract

Results of a study using a passive approach to recover the loss of lift that occurred when a variable droop leading edge (VDLE) airfoil was used to successfully control compressible dynamic stall by attach ing a small Gurney flap to it trailing edge are reported. Gurney flaps of' different heights were tested. The airfoil performance was evaluated by measuring the unsteady pressures while it executed a sinusoidal pitch -Up maneuver over a range of Mach numbers from 0.2 to 0.4 at different reduced frequencies, with both static and dynamic leading edge droops. Not only was the " lost" lift recovered completely with a 1 % chord-height Gurney flap, the drag and moment coefficients were also dramatically reduced and a lift-to-drag ratio greater than 10 was achieved, making it an acceptable choice for this purpose. The improved performance is explained through the basic fluid mechanics of the problem by discussing the various pressure distributions and the surface vorticity fluxes derived from these.