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How dorsal fin sharpness affects swimming speed and economy

  • Qiang Zhong (a1), Haibo Dong (a1) and Daniel B. Quinn (a1) (a2)

Abstract

Multi-fin systems, like fish or fish-inspired vehicles, are governed by unsteady three-dimensional interactions between their multiple fins. In particular, dorsal/anal fins have received much attention because they are just upstream of the main thrust-producing fin: the caudal (tail) fin. We used a tuna-inspired fish model with variable fin sharpness to study the interaction between elongated dorsal/anal fins and caudal fins. We found that the performance enhancement is stronger than previously thought (15 % increase in swimming speed and 50 % increase in swimming economy) and is governed by a three-dimensional dorsal-fin-induced cross-flow that lowers the angle of attack on the caudal fin and promotes spanwise flow. Both simulations and multi-layer particle image velocimetry reveal that the cross-flow stabilizes the leading edge vortex on the caudal fin, similar to how wing strakes prevent stall during fixed-wing aircraft manoeuvres. Unlike other fin–fin interactions, this mechanism is phase-insensitive and offers a simple, passive solution for flow control over oscillating propulsors. Our results therefore improve our understanding of multi-fin flow interactions and suggest new insights into dorsal/anal fin shape and placement in fish and fish-inspired vehicles.

Copyright

Corresponding author

Email address for correspondence: qz4te@virginia.edu

References

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JFM classification

Type Description Title
VIDEO
Movie

Zhong Supplementary Movie
3D PIV reveals that dorsal fin stabilizes the flow over caudal fin in M4 case compare to M1 case.

 Video (25.0 MB)
25.0 MB

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