Abstract
Much effort has been undertaken to elucidate unsteadiness in propulsion in swimming, because a quasi-steady-state approach has led to errors in predicting the fluid forces acting on a hand. It has been noted that the unsteady fluid force plays an important role in an S-shaped pull or a sculling motion of swimmer. In the present study, the vortex structure and its behavior of a discoid airfoil simulating a swimmer's hand are investigated during pitch-oscillating motion in a wind tunnel test. The vortical flow fields were measured by the scanning PIV technique. The vortex ring is successively shed downstream under stationary conditions. Furthermore, the vortex ring inclines as the angle of attack of the airfoil changes, and the inclined angle becomes smaller as the vortex ring travels downstream. On the contrary, the vortex growth is observed during pitch-oscillating motion, and large scale vortex releases into the wake close to the airfoil. The vortex becomes larger as increasing the reduced frequency.
