Effect of torsional spring and shape on the performance of bioinspired caudal fin

Abstract

The swimming ability of fish is greatly influenced by the hydrodynamics of their caudal fins. In this paper, the effects of flexibility and shape on the performance of a bioinspired panel are numerically studied. The flexibility is simplified as a torsional spring, and three typical shapes (i.e., square, convex, and concave shapes) are considered. The results are obtained based on three-dimensional numerical simulations of flapping panels at Re = 1000 and St = 0.5. It is shown that the flexibility can significantly affect the performance of pitching panels, by changing the phase lag between the motions of the fore and hind parts. When the phase lag is in the range of 0.1π–0.6π, the performance improvement can be obtained by the flexible panels, as compared with the rigid panel. Moreover, the maximum thrust (or efficiency) can be achieved by a flexible panel when the phase lag is approximately 0.35π (or 0.24π). On the other hand, it is found that the convex shape is optimal for thrust generation, but the square shape is optimal for propulsive efficiency. Moreover, the mechanism by which flexibility and shape can influence the performance of the pitching panel is analyzed. The results obtained here may provide some light on designing the efficient propulsor for microunderwater robots.