This paper addresses hydrodynamic performance of fins regarding their trailing edge convexity–concavity and flexibility distribution. The effects of trailing edge convexity–concavity on propulsive performance and vortex dynamics were investigated experimentally utilizing time-resolved particle image velocimetry and force sensors. It was found that the convex trailing edge shape always outperforms the concave shape. Wake contracting by the bent shape of the trailing edge vortex of a convex trapezoidal form resulted in higher thrust and efficiency. The results also showed that the rounded edges of fish fins did not provide additional hydrodynamic advantages. Furthermore, we found that a gradually flexible fin delivered better propulsive performance over a uniformly flexible fin. The hydrodynamic performance of the flexible fins depended on the strength and relative positions of the trailing edge vortexes shed by each fin, which were affected by the flexible deformations of the fins. In the lower Reynolds number operation (approaching, but below the first resonant mode), the fins with larger camber produced a stronger momentum footprint especially considering the far wake elements, while in the higher Reynolds number range due to resonant deformation the extent of trailing edge excursion became dominant in affecting the propulsive performance. The results showed that gradually flexible fins can improve the performance of future watercraft.

中文翻译：

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渐进柔性和后缘形状对俯仰尾翼推进性能的影响

本文讨论了鳍片后缘凸度-凹度和柔度分布的流体动力学性能。利用时间分辨粒子图像测速仪和力传感器，通过实验研究了后缘凸凹对推进性能和涡流动力学的影响。发现凸后缘形状总是优于凹形状。通过凸梯形后缘涡旋的弯曲形状收缩尾流导致更高的推力和效率。结果还表明，鱼鳍的圆形边缘没有提供额外的水动力优势。此外，我们发现逐渐柔性的鳍片比均匀柔性的鳍片提供更好的推进性能。柔性翅片的水动力性能取决于每个翅片脱落的后缘涡的强度和相对位置，这些涡流受翅片柔性变形的影响。在较低雷诺数操作中（接近但低于第一共振模式），具有较大弯度的翅片产生更强的动量足迹，特别是考虑到远尾流元素，而在较高雷诺数范围内，由于共振变形，后缘的程度偏移在影响推进性能方面占主导地位。结果表明，逐渐灵活的鳍可以提高未来船只的性能。在较低雷诺数操作中（接近但低于第一共振模式），具有较大弯度的翅片产生更强的动量足迹，特别是考虑到远尾流元素，而在较高雷诺数范围内，由于共振变形，后缘的程度偏移在影响推进性能方面占主导地位。结果表明，逐渐灵活的鳍可以提高未来船只的性能。在较低雷诺数操作中（接近但低于第一共振模式），具有较大弯度的翅片产生更强的动量足迹，特别是考虑到远尾流元素，而在较高雷诺数范围内，由于共振变形，后缘的程度偏移在影响推进性能方面占主导地位。结果表明，逐渐灵活的鳍可以提高未来船只的性能。