Flow Separation on Finite Span, Cantilevered Wings at Low Reynolds Number

Vortical structures and the associated flowfield on finite-span, cantilevered NACA 0015 wings were observed experimentally. The effects of semi-aspect ratios of 1, 2, and 4, sweep angles of 0, 15, 30, and 45 deg, at angles of attack of 12, 18, and 22 deg were explored at a Reynolds number of 600. On each wing, there are three regions along the span: a wall region, a tip region, and wake region between the two. At low semi-aspect ratios, end effects played a significant role by mitigating the shedding, resulting in a small separated region. At higher semi-aspect ratios, the wings ends had less of an influence on the overall flowfield, allowing the developments of separation and shedding in the wake. For the unswept wings, secondary structures of alternating rotation developed as a result of the interaction between the separated flow and the end regions. In the swept cases, an outboard spanwise velocity component developed, which interacted with the separated region forming secondary structures and a large dominant swirl vortex along the span. Both time-averaged and instantaneous flowfields were used to understand the formation of the structures. The present study shows the complexity of three-dimensional flow separation even on simple geometries.