Relationship between vortex ring in tail fin wake and propulsive force


Our aim was to investigate the three-dimensional (3D) vortex ring in the wake of a tail fin and to clarify the propulsion mechanism of dolphins and fish. In this study, we replaced a tail fin in pitching motion with an oscillating wing having a drive unit. The flow fields around the wing were measured by stereoscopic particle image velocimetry. To visualize the 3D structure of the vortex in the wake, we determined the flow fields in equally spaced cross-sectional planes. We reconstructed the 3D velocity fields from the velocity data with three components in two dimensions. We visualized the 3D vortex structure from these velocity data and plotted an iso-vorticity surface. As a result, we found that the vortex ring was generated by the kick-down and kick-up motions of the wing and that the wake structure was comparable with that obtained numerically. Moreover, we calculated the propulsive forces from the temporal variations in circulation and in the area surrounded by the vortex ring.

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This study was supported by a Grant-in-Aid for Challenging Exploratory Research (23650383) from the Japan Society for the Promotion of Science. The authors thank Professor Jun Sakakibara of the University of Tsukuba for providing many useful comments and the technical support for using the PIV measurement system. The authors also thank the reviewers for insightful comments and the editor for helpful guidance.

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Correspondence to Naoto Imamura.

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Imamura, N., Matsuuchi, K. Relationship between vortex ring in tail fin wake and propulsive force. Exp Fluids 54, 1605 (2013).

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  • Vortex
  • Vorticity
  • Particle Image Velocimetry
  • Vortex Ring
  • Strouhal Number