School cohesion, speed and efficiency are modulated by the swimmers flapping motion
School cohesion, speed and efficiency are modulated by the swimmers flapping motion
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DOI：
10.1017/jfm.2021.551
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发表时间：
2021-07-13
影响因子：
3.7
通讯作者：
Kanso, Eva
中科院分区：
文献类型：
--
作者：
Heydari, Sina;Kanso, Eva
鱼群在海洋生物中随处可见。尽管流动相互作用被认为有益于学习，但它们对群体的速度、能量和稳定性的确切影响仍然难以捉摸。最近的数值模拟和实验模型表明，流动相互作用稳定了扑翼的串联形成。在这里，我们使用了一个最小涡片模型，它捕捉了拍打游泳者之间流动相互作用的显著特征，并研究了两个直列式游泳者以相同的升降或俯仰运动驱动的自由游泳。我们发现，与拍打模式、起伏或俯仰无关，追随者在领先者之后的不同位置被动稳定，这与起伏花剑实验一致，但俯仰游泳者表现出更紧密和更有凝聚力的队形。此外，与单独游泳相比，俯仰运动提高了群体的能量效率，而上升运动导致游泳速度略有提高。对单个游泳者的尾流进行更深入的分析，可以揭示成对队形背后的水动力机制。这些结果概括了流动互动提供了一种促进学校凝聚力的被动机制，并对扑翼模式在控制学校涌现属性中的作用提供了新的见解。
Fish schools are ubiquitous in marine life. Although flow interactions are thought to be beneficial for schooling, their exact effects on the speed, energetics and stability of the group remain elusive. Recent numerical simulations and experimental models suggest that flow interactions stabilize in-tandem formations of flapping foils. Here, we employ a minimal vortex sheet model that captures salient features of the flow interactions among flapping swimmers, and we study the free swimming of a pair of in-line swimmers driven with identical heaving or pitching motions. We find that, independent of the flapping mode, heaving or pitching, the follower passively stabilizes at discrete locations in the wake of the leader, consistent with the heaving foil experiments, but pitching swimmers exhibit tighter and more cohesive formations. Further, in comparison to swimming alone, pitching motions increase the energetic efficiency of the group while heaving motions result in a slight increase in the swimming speed. A deeper analysis of the wake of a single swimmer sheds light on the hydrodynamic mechanisms underlying pairwise formations. These results recapitulate that flow interactions provide a passive mechanism that promotes school cohesion, and afford novel insights into the role of the flapping mode in controlling the emergent properties of the school.