Abstract
Flying and aquatic animals release a vortex by pitching a wing or a fin. It is well known that vortex motion plays an important role in generation of unsteady fluid force. However, studies on unsteady propulsion system of birds, insects, and fish are few and inconclusive. The purpose of this study investigates the effect of 3-dimensional airfoil shape on three-dimensional vortex structure in the case of the high reduced frequency. In the present study, pitch-oscillating motion was carried out as a basic unsteady motion. The vortex structure and its behaviour for a discoid airfoil and the NACA0015 airfoil are investigated. The vortical flow fields were measured by a stereo PIV technique. Two significant vortices are released during one cycle of pitching oscillating. For the NACA0015, the strong vortex is generated.
