Leading-edge vortex development on a pitching flat plate with multiple leading edge geometries

Abstract

This article investigates the dynamic stall of a pitching flat plate in order to facilitate lift control in applications such as flapping wings and micro-aerial vehicles. Constant-pitch-rate rotation, similar to ramp-and-hold, of a flat plate was investigated in an open-jet wind tunnel using embedded surface pressure sensors to assess vortex formation and its impact on aerodynamic characteristics. Three leading edge and trailing edge geometries were investigated, with all demonstrating minor effects on the overall aerodynamic performance for the angles of attack presented. For all leading and trailing edge combinations, increasing the rotation rate increased the magnitude of the localised low pressure on the upper surface the flat plate resulting in increased lift. Separation of the leading-edge vortex was characterised by the motion of a half-saddle flow feature on the upper surface of the flat plate, which in turn was linked to the rotation rate. A critical angle of attack was found whereby further increases in the angle of attack provided no benefit to overall force generation. The surface pressures shown in the current investigation can be utilised for the development of adaptive boundary layer control devices to either limit or promote the dynamic stall process on a flat plates. This study confirms that vortex lift, which is critical for flight of micro-aerial vehicles and flapping wing devices, is limited by the maximum angle of attack and rotation rate. This is significant for high-lift devices where limited power is available for lift generation.