A piv study of baseline and controlled flow over a highly deflected flap of a generic trapezoidal wing

The present study was conducted to improve the understanding of flow physics behind the highly deflected flap of a low aspect ratio, highly tapered, trapezoidal wing for baseline and actively controlled conditions. A semi-span model, based on a NACA0012 profile, was equipped with a flap hinged parallel to the trailing edge. Fluidic oscillators were installed at the trailing edge of the main element, just upstream of the flap shoulder, to increase the lift while maintaining longitudinal stability for high-lift conditions (i.e., large flap deflections). The Reynolds number in all experiments based on the root chord was 1,700,000. The flow over the flap, deflected at 55°, was analyzed for model incidences of 0° and 8° respectively using particle image velocimetry. Various planes parallel to the flap surface were measured in order to create a volumetric flow field. The baseline and controlled cases were analyzed and compared to surface flow visualization data, including tuft images and pressure sensitive paint. A strong flap leading edge vortex was detected at 0° incidence and active flow control limits the influence of this structure. Nevertheless, full attachment of the flow was not possible for this condition. For higher incidence (i.e., 8°), the actuators had a larger impact and attached the otherwise separated flow. This study shows that an array of fluidic oscillators is well suited to reattach massively separated flow over the flap of a low aspect ratio, highly tapered, trapezoidal wing. The control is less effective when the flow is partially attached due to the influence of the flap leading edge vortex.