Aerodynamics of Gurney flaps on a single-element high-lift wing

The trailing-edge region of a single-element wing fitted with Gurney flaps has been studied. Measurements include surface pressure, force, and velocity by laser Doppler anemometry (LDA). The mean-velocity vectors and streamlines suggest a twin vortex structure downstream of the Gurney flap. Spectral analysis of the LDA data indicates that the wake consists of a von Karman vortex street of alternately shed vortices, and this flow structure is confirmed by smoke visualization of the flow downstream of the Gurney flap. The vortex shedding increases the trailing-edge suction of the aerofoil, whereas the upstream face of the device decelerates the flow at the trailing edge of the pressure surface. These two changes result in a pressure difference acting across the trailing edge, and it is this that generates the increase in circulation.