A Numerical Study of Metachronal Propulsion at Low to Intermediate Reynolds Numbers
A Numerical Study of Metachronal Propulsion at Low to Intermediate Reynolds Numbers
复制标题
DOI：
10.3390/fluids5020086
复制
发表时间：
2020-06-01
期刊：
影响因子：
1.9
通讯作者：
Zhang-Molina, Calvin
中科院分区：
文献类型：
--
作者：
Granzier-Nakajima, Shawtaroh;Guy, Robert D.;Zhang-Molina, Calvin
受长尾甲壳类动物向前游泳的启发，我们研究了一种水下推进机制，该机制用于游泳体，该游泳体具有多个刚性桨，连接在下面，经历动力和返回冲程的循环，相邻桨之间具有恒定的相位差，这种现象称为异时推进。为了研究桨间相位差如何影响通量的产生，我们开发了一个计算流体动力学模型和基于浸没边界法的数值算法，这使我们能够模拟雷诺数（RE）范围从接近0到约100的异时推进。我们的主要发现是，最高的平均通量时，最近的邻居桨保持约20%-25%的相位差与更后桨领先的周期，这一结果是独立的中风频率在整个范围内的RE这里考虑。我们还发现，最佳桨间距和桨的数量取决于RE，我们看到一个质的转变，由异时推进所产生的流的动态RE上升到80以上。粗略地说，就平均通量产生而言，当RE小于10时，优选紧密的桨间距，但当RE接近或高于100时，较宽的间距变得明显有利。在通量产生效率方面，在RE 0.1时，最大效率出现在两个桨叶处，并且效率随着桨叶数量的增加而降低。在RE 100处，效率随着桨片数量的增加而增加，并且似乎通过八个桨片而饱和，而使用四个桨片对于低RE和中等RE两者都是良好的折衷。
Inspired by the forward swimming of long-tailed crustaceans, we study an underwater propulsion mechanism for a swimming body with multiple rigid paddles attached underneath undergoing cycles of power and return strokes with a constant phase-difference between neighboring paddles, a phenomenon known as metachronal propulsion. To study how inter-paddle phase-difference affects flux production, we develop a computational fluid dynamics model and a numerical algorithm based on the immersed boundary method, which allows us to simulate metachronal propulsion at Reynolds numbers (RE) ranging from close to 0 to about 100. Our main finding is that the highest average flux is generated when nearest-neighbor paddles maintain an approximate 20%-25% phase-difference with the more posterior paddle leading the cycle; this result is independent of stroke frequency across the full range of RE considered here. We also find that the optimal paddle spacing and the number of paddles depend on RE; we see a qualitative transition in the dynamics of flow generated by metachronal propulsion as RE rises above 80. Roughly speaking, in terms of average flux generation, a tight paddle spacing is preferred when RE is less than 10, but a wider spacing becomes clearly favored when RE is close to or above 100. In terms of efficiency of flux generation, at RE 0.1 the maximum efficiency occurs at two paddles, and the efficiency decreases as the number of paddles increases. At RE 100 the efficiency increases as the number of paddles increases, and it appears to saturate by eight paddles, whereas using four paddles is a good tradeoff for both low and intermediate RE.