Vortex Shedding from a Pitch-Oscillating Discoid Airfoil

概要

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Flying and aquatic animals release a vortex by pitching a wing or a fin. The behavior of this vortex affects unsteady fluid forces, and the propulsive force of these animals relates to unsteady forces accompanied with the movement of vortices. It is well known that vortex motion plays an important role in the generation of unsteady fluid force and enhancement of the force. In general, the force associated with unsteady flow is greater than that of steady flow. Accordingly, conventional quasi-steady theory cannot give the correct assessment of the generating mechanism of the propulsive force. In the present study, generation of the propulsive force in swimming is investigated. The vortex structure and its behavior owing to flow around a discoid airfoil simulating a swimmers hand are investigated during pitch-oscillating motion. In particular, wind tunnel tests were conducted to investigate the relationship between three-dimensional vortex structure and unsteady fluid forces acting on a discoid airfoil. The vortical flow fields were measured using a scanning particle image velocimetry technique. Under stationary conditions, the vortex ring is successively shed downstream, and the vortex ring inclines as the angle of attack α of the airfoil changes. On the contrary, vortex growth is observed during pitch-oscillating motion, and a large scale vortex is released into the wake close to the airfoil.
日本実験力学会の論文