Span-distributed Coverts-inspired Flow Control Devices

The coverts are contour feathers that cover the upper and lower surfaces of bird wings. Studies in biology suggest that upper wing coverts act as aeroelastic flow control devices to control flow separation and mitigate stall. Previous studies by the authors show that torsionally hinged coverts-inspired flaps mounted at different chord-wise locations on the suction side of a 2D airfoil and a 3D finite wing can enhance lift post-stall by up to 20% in both cases at a Reynolds number of 200,000. In these studies, the flaps covered the entire span of the wing, neglecting the span-wise spatial distribution of the flap. In this study, we investigate the effect of the span-wise length and distribution of covert-inspired flaps on the post-stall aerodynamics of a finite wing with an aspect ratio AR = 4.6 at a Re of 200,000. This aspect ratio was chosen due to its biological relevance, especially for birds of prey that fly at a similar Reynolds number range. More specifically, using wind tunnel experiments and time-resolved PIV, we will examine the fluid-structure interaction mechanisms of a rectangular wing with suction side span-distributed flaps. Results will show the effects of changing the hinge stiffness, flap inertia, and flap location of multiple span-distributed flaps on the aerodynamic performance of the wing post-stall and tall propagation. Moreover, we will examine the effect of the 3D flow field (i.e. spanwise flow and wingtip vortices) on the deployment dynamics of the flaps, especially how the flap behavior changes as a function of its location along both the chord and span.