A quantitative study of the lift-enhancing flow field generated by an airfoil with a Gurney flap.

Abstract

Although it is well known that a Gurney flap affects the lift, drag, and pressure distribution along an airfoil, the mechanisms behind the changes are still not well understood. The following research seeks to understand what is causing the effects of a Gurney flap through quantitative measurements of the spatial and temporal flow details, including force balance measurements, hotwire anemometry (HWA), high resolution particle image velocimetry (HRPIV), and time resolved particle image velocimetry (TRPIV). TRPIV is used to broaden the understanding of the interaction between the various vortex shedding modes which are elicited from the regions upstream and downstream of the flap. The HWA technique is useful for its very high frequency response, and is used in the wake of the airfoil in order to gain valuable insight into the nature of the vortex shedding frequencies. Vortices generated both upstream and downstream of the Gurney flap have been observed, and the vortex interactions, which occur due to the non-phase-locked nature of the shedding modes, are analyzed. The results are interpreted in terms of the known lift increment.