Abstract
Recently, much attention is paid to fin-swimming. Many researches have been conducted on the fin itself and swimming with fin, but many of them did not consider unsteady flow effect. Monofin moves intensively and hence the unsteady fluid force should be taken into account. The fluid force is closely related to the generation of vortices. It is widely known that the monofin itself has the thrust from the fluid by shedding vortices. However, the relation between the thrust and the generation of vortices has not been clarified in detail. In this study, we visualize the flow field around a monofin in pitching motion using the Particle Image Velocimetry (PIV) and also measure the thrust generated by the fin. We clarify the relation between the thrust and the generation of vortices in detail. When the propulsion is large, vortices of high intensity were generated in the wake of the monofin. It was found that the propulsion is larger for higher pitching frequency of mnofin and also the non-dimensional time at the peak of propulsion is delayed.
