Abstract
Flying and aquatic animals release a vortex by pitching a wing or a fin. The behavior of this vortex affects unsteady fluid forces. The role of unsteadiness is critical in the generation of momentum and therefore in the force generation. That is, the unsteady forces must also be considered when estimating the propulsive force of swimming doing the front crawl. 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 to elucidate the relationship between three- dimensional vortex structure and unsteady fluid forces. The vortex growth is observed during pitch-oscillating motion, and large scale vortex is released into the wake of the airfoil. Furthermore, the peak value of fluid force for the case of changing in speed during one pitch-oscillating motion becomes larger.
