Abstract We experimentally investigated the fluid-structure interaction (FSI) and energy extraction performance of a novel flapping-foil based flow-energy harvester. Different from most of existing concepts, this device can extract energy from flows through a foil's fully passive flapping motion, i.e., the foil's heaving and pitching motions are induced by the flow without using any actuator. The foil's dynamics and energy extraction performance were studied under various flow and operating conditions. It was found that, when operating at the Reynolds number near 105, the device has a cut-in speed of 0.45 m/s and can generate a mean power of about 1 W in a water flow of 0.55 m/s, leading to a power conversion efficiency of 32.5%. Detailed FSI studies revealed that both the heaving and pitching motions can make positive contributions to energy harvesting. The heaving velocity reaches its extremes at the end of each pure heaving phase, whereas the heaving force reaches its extremes at around the end of each stroke reversal, leading a phase difference of nearly 90°. As such, the heaving power is positive in the pure heaving phases but negative in the stroke reversal phases. Both the pitching velocity and pitching moment peak at the end of stroke reversals, hence generating a significant peak in the pitching power. It was also found that, compared to the foil's effective angle of attack, the leading-edge vortices produced during flapping have a very limited impact on the foil's dynamics. A parametric study revealed that, as the foil's pivot axis is moved towards the trailing edge, both the mean heaving power and the mean pitching power increase. As a result, the total power increases significantly. The same trend was also observed when the foil's pitching amplitude increases from 30° to 60°. On the contrary, it seems that there exists an optimal water speed between 0.46 and 0.69 m/s, at which the power conversion efficiency is maximum.

中文翻译：

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用于流动能量提取的全被动拍打箔的流固耦合

摘要 我们通过实验研究了一种新型基于扑翼的流动能量收集器的流固耦合 (FSI) 和能量提取性能。与大多数现有概念不同，该装置可以通过水翼完全被动的拍动运动从流动中提取能量，即水翼的起伏和俯仰运动是由流动引起的，而无需使用任何致动器。在各种流动和操作条件下研究了箔的动力学和能量提取性能。发现当雷诺数接近 105 时，该装置的切入速度为 0.45 m/s，在 0.55 m/s 的水流中可产生约 1 W 的平均功率，导致32.5%的电源转换效率。详细的 FSI 研究表明，升沉和俯仰运动都可以对能量收集做出积极贡献。升沉速度在每个纯升沉阶段结束时达到极限，而升沉力在每个冲程反转结束时达到极限，导致接近 90°的相位差。因此，升沉功率在纯升沉阶段为正，而在冲程反转阶段为负。俯仰速度和俯仰力矩都在冲程反转结束时达到峰值，因此在俯仰功率中产生了显着的峰值。还发现，与翼的有效攻角相比，在拍打过程中产生的前缘涡流对翼的动力学影响非常有限。一项参数研究表明，作为箔' s 枢轴向后缘移动，平均升沉功率和平均俯仰功率均增加。结果，总功率显着增加。当箔片的俯仰幅度从 30° 增加到 60° 时，也观察到相同的趋势。相反，似乎在 0.46 到 0.69 m/s 之间存在一个最佳水速，在该处功率转换效率最大。