Li Ningyu, Liu Huanxing, Su Yumin
Science and Technology on Underwater Vehicle Laboratory, Harbin Engineering University, Harbin, China.
Beijing Institute of Specialized Machinery, Beijing, China.
PLoS One. 2017 Mar 31;12(3):e0174740. doi: 10.1371/journal.pone.0174740. eCollection 2017.
Numerical simulations are employed to study the hydrodynamics of self-propelled thunniform swimming. The swimmer is modeled as a tuna-like flexible body undulating with kinematics of thunniform type. The wake evolution follows the vortex structures arranged nearly vertical to the forward direction, vortex dipole formation resulting in the propulsion motion, and finally a reverse Kármán vortex street. We also carry out a systematic parametric study of various aspects of the fluid dynamics behind the freely swimming behavior, including the swimming speed, hydrodynamic forces, power requirement and wake vortices. The present results show that the fin thrust as well as swimming velocity is an increasing function of both tail undulating amplitude Ap and oscillating amplitude of the caudal fin θm. Whereas change on the propulsive performance with Ap is associated with the strength of wake vortices and the area of suction region on the fin, the swimming performance improves with θm due to the favorable tilting of the fin that make the pressure difference force more oriented toward the thrust direction. Moreover, the energy loss in the transverse direction and the power requirement increase with Ap but decrease with θm, and this indicates that for achieving a desired swimming speed increasing θm seems more efficiently than increasing Ap. Furthermore, we have compared the current simulations with the published experimental studies on undulatory swimming. Comparisons show that our work tackles the flow regime of natural thunniform swimmers and follows the principal scaling law of undulatory locomotion reported. Finally, this study enables a detailed quantitative analysis, which is difficult to obtain by experiments, of the force production of the thunniform mode as well as its connection to the self-propelled swimming kinematics and vortex wake structure. The current findings help provide insights into the swimming performance and mechanisms of self-propelled thunniform locomotion.
采用数值模拟方法研究自推进式金枪鱼状游动的流体动力学。游泳者被建模为具有金枪鱼状的柔性身体，以金枪鱼式的运动学方式波动。尾流演变遵循几乎垂直于前进方向排列的涡旋结构，涡旋偶极子的形成导致推进运动，最终形成反向卡门涡街。我们还对自由游动行为背后的流体动力学的各个方面进行了系统的参数研究，包括游泳速度、流体动力、功率需求和尾流涡旋。目前的结果表明，鳍推力以及游泳速度是尾鳍摆动幅度Ap和尾鳍振荡幅度θm的增函数。Ap对推进性能的影响与尾流涡旋的强度和鳍上吸力区域的面积有关，而游泳性能随θm的增加而提高，这是因为鳍的有利倾斜使压力差力更倾向于推力方向。此外，横向能量损失和功率需求随Ap增加而增加，但随θm减小而减小，这表明为了达到所需的游泳速度，增加θm似乎比增加Ap更有效。此外，我们将当前的模拟结果与已发表的关于波动游动的实验研究进行了比较。比较表明我们的工作处理了自然金枪鱼式游泳者的流动状态，并遵循了所报道的波动运动的主要比例定律。最后，这项研究能够对金枪鱼式模式的力产生及其与自推进游泳运动学和涡旋尾流结构的联系进行详细定量分析，而这很难通过实验获得。目前的研究结果有助于深入了解自推进式金枪鱼式运动的游泳性能和机制。
