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. We intend to elucidate the relationship between unsteady fluid forces and three-dimensional vortex structure in the case of the greater reduced frequency. In the present study, pitch-oscillating motion was carried out as a basic unsteady motion. The vortex structure and its behaviour of a discoid airfoil are investigated during pitch-oscillating. The vertical flow fields were measured using a stereo PIV technique. The vortex growth is observed during pitch-oscillating motion, and large scale vortex is released into the wake close to the airfoil. It was confirmed that two significant vortices are released during one cycle of pitching oscillating and the fluid force shows a peak value at the instant of the vortex shedding.
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