Wang Junshi, Wainwright Dylan K, Lindengren Royce E, Lauder George V, Dong Haibo
Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22904, USA.
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
J R Soc Interface. 2020 Apr;17(165):20190590. doi: 10.1098/rsif.2019.0590. Epub 2020 Apr 8.
Finlets are a series of small non-retractable fins common to scombrid fishes (mackerels, bonitos and tunas), which are known for their high swimming speed. It is hypothesized that these small fins could potentially affect propulsive performance. Here, we combine experimental and computational approaches to investigate the hydrodynamics of finlets in yellowfin tuna () during steady swimming. High-speed videos were obtained to provide kinematic data on the motion of finlets. High-fidelity simulations were then carried out to examine the hydrodynamic performance and vortex dynamics of a biologically realistic multiple-finlet model with reconstructed kinematics. It was found that finlets undergo both heaving and pitching motion and are delayed in phase from anterior to posterior along the body. Simulation results show that finlets were drag producing and did not produce thrust. The interactions among finlets helped reduce total finlet drag by 21.5%. Pitching motions of finlets helped reduce the power consumed by finlets during swimming by 20.8% compared with non-pitching finlets. Moreover, the pitching finlets created constructive forces to facilitate posterior body flapping. Wake dynamics analysis revealed a unique vortex tube matrix structure and cross-flow streams redirected by the pitching finlets, which supports their hydrodynamic function in scombrid fishes. Limitations on modelling and the generality of results are also discussed.
小鳍是鲭科鱼类（鲭鱼、鲣鱼和金枪鱼）所共有的一系列小型不可收缩的鳍，这些鱼类以其高游泳速度而闻名。据推测，这些小鳍可能会影响推进性能。在此，我们结合实验和计算方法来研究黄鳍金枪鱼在稳定游泳过程中小鳍的流体动力学。通过高速视频获取了小鳍运动的运动学数据。然后进行了高保真模拟，以研究具有重建运动学的生物逼真的多小鳍模型的流体动力学性能和涡旋动力学。研究发现，小鳍会进行升沉和俯仰运动，并且沿身体从前向后相位延迟。模拟结果表明，小鳍产生阻力而不产生推力。小鳍之间的相互作用使小鳍总阻力降低了21.5%。与不俯仰的小鳍相比，小鳍的俯仰运动使游泳过程中小鳍消耗的功率降低了20.8%。此外，俯仰的小鳍产生了建设性的力，以促进身体后部的摆动。尾流动力学分析揭示了一种独特的涡管矩阵结构以及由俯仰小鳍重新定向的横流，这支持了它们在鲭科鱼类中的流体动力学功能。还讨论了建模的局限性和结果的普遍性。
