Hydrodynamics of metachronal paddling: effects of varying Reynolds number and phase lag
Hydrodynamics of metachronal paddling: effects of varying Reynolds number and phase lag
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DOI：
10.1098/rsos.191387
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发表时间：
2019-10-01
影响因子：
3.5
通讯作者：
Santhanakrishnan, Arvind
中科院分区：
文献类型：
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作者：
Ford, Mitchell P.;Lai, Hong Kuan;Santhanakrishnan, Arvind
负浮力自由游动的甲壳类动物，如磷虾，必须产生向下的动量，以保持它们在水柱中的位置。这些动物使用基于阻力的推进策略，其中成对的紧密间隔的游泳肢从尾部到头部有节奏地摆动。每一对相对于相邻对以相位延迟振荡，导致在动物运动方向上行进的异时波。目前还不清楚在水平面上的肢体振荡如何产生垂直动量。使用粒子图像测速测量的机器人模型，我们观察到，异时划桨与非零相位滞后创建的几何形状的相邻桨，促进形成反向旋转的涡流。这些涡流的相互作用导致产生大规模的倾斜向下射流。增加相位滞后导致更多的垂直方向的射流，和相位滞后的范围内使用的南极磷虾产生的总动量。同步划水产生较低的总动量时，与异时划水。将雷诺数降低一个数量级，低于成年磷虾的范围（250-1000），表明射流的向下传播减少，垂直动量降低。我们的研究结果表明，异时划桨能够产生流动，可以产生快速向前游泳和悬停所需的升力（垂直）和推力（水平）。
Negatively buoyant freely swimming crustaceans such as krill must generate downward momentum in order to maintain their position in the water column. These animals use a drag-based propulsion strategy, where pairs of closely spaced swimming limbs are oscillated rhythmically from the tail to head. Each pair is oscillated with a phase delay relative to the neighbouring pair, resulting in a metachronal wave travelling in the direction of animal motion. It remains unclear how oscillations of limbs in the horizontal plane can generate vertical momentum. Using particle image velocimetry measurements on a robotic model, we observed that metachronal paddling with non-zero phase lag created geometries of adjacent paddles that promote the formation of counter-rotating vortices. The interaction of these vortices resulted in generating large-scale angled downward jets. Increasing phase lag resulted in more vertical orientation of the jet, and phase lags in the range used by Antarctic krill produced the most total momentum. Synchronous paddling produced lower total momentum when compared with metachronal paddling. Lowering Reynolds number by an order of magnitude below the range of adult krill (250-1000) showed diminished downward propagation of the jet and lower vertical momentum. Our findings show that metachronal paddling is capable of producing flows that can generate both lift (vertical) and thrust (horizontal) forces needed for fast forward swimming and hovering.