Vortex capture by a two-dimensional airfoil with a small oscillatingleading-edge flap

Abstract

In order to exploro the possibility of capturing a vortex an the upper surface of an airfoil at high angle of attack by unsteady excitations, a sharp-leading~edge airfoil with ascil- lating leading edge flap was testcd in a low speed wind tunncl and simulated by numerical compulation. The most important experimental result is that a 60%-70% of lift increment was achicved with little or even no penalty on drag at post stall condition, when the excitation changed the massively sepa- rated flow to a closed separation bubble in the mean sense, and thus held a strong vortex on the upper surface of the airfoil. As a complement to this experimentally obtained time-averagcd picture, preliminary numerical compulation revealed tlic cor- responding instantaneous process. The result shows that, with excitation, vortices are still shedding, but the probability of a wcll-organized lifting vortex staying above the airfoil is much larger than that without excitation. This finding suggests a potential of designing innovative higli~lift airfoils and wings.