AML, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, People's Republic of China.
Department of Mechanical Engineering, KAIST, Daejeon 34141, Republic of Korea.
Bioinspir Biomim. 2022 Sep 16;17(6). doi: 10.1088/1748-3190/ac84b8.
Tuna, which are known for high-performance swimming, possess a large crescent dorsal fin (DF) and a caudal fin (CF) that differ from those of other fishes. The hydrodynamic interaction between the DF and CF in tuna, which are represented by two tandem 3D flapping plates, is numerically explored in the present study. Hydrodynamic properties and wake structures of the models with and without a DF are compared to investigate the effects of the DF. The thrust on the CF is substantially enhanced by the DF, whereas the force on the DF is not affected by the CF. The constructive interaction between the leading-edge vortex (LEV) on the CF and the vortices shed from the dorsal fin (DFVs) is identified from 3D wake topology and 2D vorticity distributions. The circulation of spanwise vorticity quantitatively reveals that the LEV on the CF is strengthened by the same-signed DFV. The effect of the flapping phase of the CF is examined. The DF-CF interaction is sensitive to the flapping phase at a short spacing, whereas a long spacing between the two fins enables a robust constructive interaction in tuna swimming. A systematic study is carried out to explore the effects of the Strouhal number (St) and the Reynolds number (Re) on the interaction of the fins. The enhancement of thrust due to the DF is diminished at St = 0.63, whereas the Re does not substantially influence the constructive DF-CF interaction.
金枪鱼以其出色的游泳能力而闻名，它们拥有一个大的新月形背鳍（DF）和一个尾鳍（CF），与其他鱼类的鳍不同。本研究通过数值方法探讨了金枪鱼中 DF 和 CF 之间的水动力相互作用，DF 和 CF 由两个串联的 3D 扑翼板代表。比较了有无 DF 的模型的水动力特性和尾流结构，以研究 DF 的影响。DF 显著增强了 CF 的推力，而 CF 对 DF 的力没有影响。从 3D 尾流拓扑和 2D 涡度分布中识别出 CF 上的前缘涡（LEV）和来自背鳍的涡（DFVs）之间的建设性相互作用。螺旋涡度的循环定量揭示了 CF 上的 LEV 被相同符号的 DFV 加强。还检查了 CF 扑动相位的影响。在短间距下，DF-CF 相互作用对 CF 的扑动相位敏感，而两个鳍之间的长间距使金枪鱼游泳中的这种相互作用更加稳健。进行了系统研究以探讨 Strouhal 数（St）和雷诺数（Re）对鳍相互作用的影响。由于 DF 导致的推力增强在 St = 0.63 时减小，而 Re 对建设性的 DF-CF 相互作用没有显著影响。
