Arrangement and Dynamic Behavior of Vortices from a Pitching Airfoil

Dynamic behavior of vortices generated behind the leading and trailing edges of pitching airfoils such as two kinds of flat plates, NACA0010, 0020, 65-0910 and an airfoil with a blunt trailing edge has been visualized using a schlieren technique with a high-speed camera in a wind tunnel. It was observed that small vortices were shed discretely from the leading and trailing edges. The frequency of vortex shedding was strongly dependent on the nondimensional pitching rate and was independent of the airfoil configuration as well as the Reynolds number. The frequecy of vortex shedding from the respective edge during one pitching cycle was the same and this result was observed similarly among all the test airfoils. Vortices existed which moved up from the trailing edge toward the leading edge on the suction surface and they played an important role in balancing the frequency of vortex shedding from the respective edge.