Wake Dynamics of Finite Aspect Ratio Wings. Part I: An Experimental Study

Abstract

The wake dynamics behind a finite span, cantilevered NACA0015 airfoil was explored experimentally using flow visualization and Stereo Particle Image Velocimetry (SPIV). Two aspect ratio wings (AR = 2 and 6) were tested at a chord-based Reynolds number of 600, angles of attacks of 12 • and 22 • , and sweep angles of 0 • and 30 •. The experiments were conducted at Rensselaer Polytechnic Institute's low speed closed return water tunnel. From the flow visualization studies it was observed that the spanwise velocity component plays a major role in the flow field as dye lines were seen to be pulled along the span for both sweep cases. The effect of the interaction of the wall boundary layer with the airfoil (resulting in a neckless vortex at the airfoil's root) and the presence of the wing tip vortex is pronounced across the span, especially for aspect ratio of 2. In the swept case, vortex shedding, due to flow separation, was significantly reduced due to the presence of sweep. The reduction in separation severity was also quantified using wake measurements via SPIV. It was also observed that for the swept wings, the strength of the tip vortex was reduced substantially due to the pronounced outboard spanwise velocity component. Preliminary comparison with numerical simulations showed very good agreement with more to follow. Future studies will involve changes in boundary conditions, sweep angles, aspect ratios, as well as higher Reynolds numbers.