Research Center for Fluid-Structure Interactions, Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, People's Republic of China.
Bioinspir Biomim. 2019 Oct 11;14(6):064002. doi: 10.1088/1748-3190/ab45d9.
This study investigates how dynamically adjusting the bending stiffness of a heaving foil affects its propulsion performance in a flow of Reynolds number 200. The foil is forced to oscillate sinusoidally at the leading edge, and its bending stiffness is tuned in a square-wave manner. Such a fluid-structure interaction (FSI) problem is explored using an immersed boundary lattice Boltzmann method (IBLBM) based numerical framework. The results reveal that when the lower and upper bounds of the foil's time-dependent bending stiffness are moderate, the net thrust can be evidently enhanced compared to those in the corresponding constant-bending-stiffness cases, while the propulsion efficiency is not apparently ameliorated. The most significant enhancement is observed when the bending stiffness has lower and upper bounds of the same duration (i.e. a duty cycle of 1/2) and also it remains at the lower bound during stroke reversals (corresponding to an actuation phase angle of [Formula: see text]). When the two bounds simultaneously increase or decrease, however, dynamically adjusting the bending stiffness fails to improve the net thrust. Through this study, competitions among various forces/moments, including the inertial force, tension force, bending moment and fluid loading, acting on the foil and their influences on the foil's dynamics are also unveiled.
本研究探讨了在雷诺数为 200 的流场中，动态调整升力翼的弯曲刚度如何影响其推进性能。翼片在前缘处强迫正弦振动，其弯曲刚度以方波方式进行调整。使用基于浸入边界格子玻尔兹曼方法（IBLBM）的数值框架探索了这种流固交互（FSI）问题。结果表明，当翼片的时变弯曲刚度的下限和上限适中时，与相应的恒弯曲刚度情况相比，净推力可以明显增强，而推进效率没有明显改善。当弯曲刚度的下限和上限具有相同的持续时间（即占空比为 1/2）并且在冲程反转期间保持在下限时，观察到最大的增强（对应于激励相位角为 [公式]）。然而，当两个边界同时增加或减少时，动态调整弯曲刚度无法提高净推力。通过这项研究，揭示了作用在翼片上的各种力/力矩（包括惯性力、张力、弯矩和流体载荷）之间的竞争及其对翼片动力学的影响。
