WING TIP VORTEX DEVELOPMENT UNDER A GRID GENERATED TURBULENT FLOW

The interaction of a NACA 0012 wingtip vortex with a grid generated flow was investigated in this paper. The experiments were conducted in the near and mid-wakes regions at three free stream turbulence (FST) levels of 0.5% (empty wind tunnel), 3% and 6%, and at two Reynolds numbers, based on the wing chord length, of 2 x10(5) and 3 x10(5). Stereoscopic Particle Image Velocimetry (SPIV) and hot wire measurements were carried out at four downstream positions, namely x/c=0.5, 2.5, 5 and 7. Streamwise velocity contours showed that the wingtip vortex decayed with increased FST and downstream distance. In the vortex core region, the streamwise velocity decelerated while the vortex adopted a wake-like profile. FST was found to decrease the vortex circulation, to increase the vortex radius, and to increase the vortex meandering amplitude. By increasing the Reynolds number, the grid cases showed a small variation of the vortex radius and vorticity peak, particularly at downstream positions of 5 and 7. With meandering correction, the turbulence level within the vortex core were found to be reduced as the artificial turbulence induced by the vortex meandering was removed.