Arrangement and Dynamic Behavior of Vortices from a Pitching Airfoil

Abstract

Most of experimental visualization and numerical results on the flow field separated from a leading edge around a moving airfoil show a continuous streakline from the leading edge and big reverse flow between the streakline and the suction surface. However, they have not exactly clarified yet the dynamic behavior of vortices separated from the leading edge because unsteady separation around a moving airfoil is very complicated phenomenon due to many parameters. In the present study the flow fields around pitching airfoils have been visualized by using a schlieren method with a high speed camera in a wind tunnel at low Reynolds number region. It has been observed that small vortices are shed discretely from the leading and trailing edge and that they stand in line on the integrated streakline of separation shear layer. By counting vortices in the VTR frames it was clarified that the number of vortex shedding from the leading and trailing edge during one pitching cycle strongly depends on the non-dimensional pitching rate. Furthermore, the vortices moving up to the leading edge on the suction surface of the pitching airfoil are visualized. They play an important role to balance the number of vortex shedding from both edges.