Swimming fishes exhibit remarkable diversities of the caudal fin geometries. In this work, a computational study is conducted to investigate the effects of the caudal fin shape on the hydrodynamic performance and wake patterns in flapping propulsion. We construct the propulsor models in different shapes by digitizing the real caudal fins of fish across a wide range of species spanning homocercal tails with low aspect ratio (square shape used by bluegill sunfish, rainbow trout, etc.) or high aspect ratio (lunate shape adopted by tuna, swordfish, etc.), and even heterocercal caudal fin adopted by sharks. Those fin models perform the same flapping motion in a uniform flow to mimic fish’s forward swimming. We then simulate the flow around the flapping fins by an in-house immersed-boundary-method based flow solver. According to the analysis of the hydrodynamic performance, we have found that the lunate shape model (high aspect-ratio) always generates a larger thrust compared to other models. The comparison of the propulsive efficiency shows that the large aspect ratio fins (tuna and shark) have a higher efficiency when the Strouhal number (St) is in the range of steady swimming (0.2<St<0.4), while the lower aspect ratio caudal fins (catfish, trout, etc.) are more efficient when St>0.4, in which the fish is accelerating or maneuvering. Finally, the 3D wake patterns of those propulsors are analyzed in detail.
- Fluids Engineering Division
Effects of Tail Geometries on the Performance and Wake Pattern in Flapping Propulsion
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Liu, G, & Dong, H. "Effects of Tail Geometries on the Performance and Wake Pattern in Flapping Propulsion." Proceedings of the ASME 2016 Fluids Engineering Division Summer Meeting collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels. Volume 1B, Symposia: Fluid Mechanics (Fundamental Issues and Perspectives; Industrial and Environmental Applications); Multiphase Flow and Systems (Multiscale Methods; Noninvasive Measurements; Numerical Methods; Heat Transfer; Performance); Transport Phenomena (Clean Energy; Mixing; Manufacturing and Materials Processing); Turbulent Flows — Issues and Perspectives; Algorithms and Applications for High Performance CFD Computation; Fluid Power; Fluid Dynamics of Wind Energy; Marine Hydrodynamics. Washington, DC, USA. July 10–14, 2016. V01BT30A002. ASME. https://doi.org/10.1115/FEDSM2016-7691
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