An investigation into the aerodynamics of gurney flaps

Abstract

The Gurney flap is a simple device for increasing the normal force (lift or downforce) generated by a wing. This thesis presents results from different experimental and computational techniques, which are used to examine the aerodynamics of the Gurney flap.

Time-averaged off-surface velocities, obtained using Laser Doppler Anemometry, confirm the hypothesis that the dominant features directly downstream of the Gurney flap are two counter-rotating vortices. The instantaneous flow structure actually consists of a wake of alternatively shed vortices, which form a von Karman vortex street.

The vortex shedding and the deceleration of the flow caused by the upstream face of the Gurney flap centre a pressure difference acting across the trailing edge, and it is this that generates the increase in circulation. Arguments are put forward that explain the observed variations in shedding frequency, trailing-edge pressures and suctions, lift and drag in Gurney flap height, incidence and sectional properties.

The effect of the Gurney flap on chordwise pressures can be simulated in a three-dimensional panel method by extending the trailing edge of the aerofoil.

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