Vortex Structure and Scale on an Unsteady Airfoil(<Special Issue>Jets, Wakes and Separated Flows)

In order to clarify vortex structures and vortex scales on an unsteady airfoil in a low Reynolds number region, we have visualized the flow around unsteady airfoils, such as a pitching airfoil and a heaving airfoil, at Re=4000 using two visualization techniques, dye flow and schlieren visualizations. In particular, we focus on dynamic behaviors of vortices shed from a leading edge, the number of vortex sheddings and their scales. At a low nondimensional pitching rate in a pitching airfoil, a number of discrete vortices were shed from the leading edge and their scale was markedly small. At a high nondimensional pitching rate in a pitching airfoil, on the other hand, the number of vortex sheddings from the leading edge in one cycle was low. However, their scale was approximately one-fourth the chord length.