Propulsion efficiency and imposed flow fields of a copepod jump
Propulsion efficiency and imposed flow fields of a copepod jump
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DOI：
10.1242/jeb.049288
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发表时间：
2011-02-01
影响因子：
2.8
通讯作者：
Kiorboe, Thomas
中科院分区：
文献类型：
--
作者：
Jiang, Houshuo;Kiorboe, Thomas
浮游桡足类跳跃以重新定位，攻击猎物和逃避捕食者。然而，这些跳跃在能量消耗和它们向趋流性捕食者产生的水动力信号方面是要付出代价的。使用所观察到的运动学的各种类型的跳跃，我们计算了强加的流场和相关的能量学的跳跃通过计算流体动力学模拟模拟的桡足类动物作为一个自我推进的机构。粒子图像测速数据验证了计算流体力学模拟的正确性。由重新定位跳跃产生的流场迅速演变成两个反向旋转的粘性涡环，它们几乎是彼此的镜像，一个在尾流中，一个在桡足类动物的身体周围;这种近似对称的流可以提供流体动力学伪装，因为它不包含关于流结构内桡足类动物猎物的位置的信息。与逃逸跳跃序列相关的流场还包括两个主要的涡结构：一个是由于第一次跳跃而产生的尾涡，另一个是围绕身体产生的，但在这两个涡结构之间是一个细长的，持久的流径，其流速矢量指向桡足类动物;这样的流场可以告知捕食者逃逸的桡足类动物猎物的下落。高弗劳德推进效率（0.94-0.98），获得了所有模拟跳跃的个人动力冲程持续时间。这对小型水生生物来说是不寻常的，但这是由于跳跃的快速和冲动造成的，只允许低成本的粘性尾涡向后移动。
Pelagic copepods jump to relocate, to attack prey and to escape predators. However, there is a price to be paid for these jumps in terms of their energy costs and the hydrodynamic signals they generate to rheotactic predators. Using observed kinematics of various types of jumps, we computed the imposed flow fields and associated energetics of jumps by means of computational fluid dynamics simulations by modeling the copepod as a self-propelled body. The computational fluid dynamics simulation was validated by particle image velocimetry data. The flow field generated by a repositioning jump quickly evolves into two counter-rotating viscous vortex rings that are near mirror image of one another, one in the wake and one around the body of the copepod; this near symmetrical flow may provide hydrodynamic camouflage because it contains no information about the position of the copepod prey within the flow structure. The flow field associated with an escape jump sequence also includes two dominant vortex structures: one leading wake vortex generated as a result of the first jump and one around the body, but between these two vortex structures is an elongated, long-lasting flow trail with flow velocity vectors pointing towards the copepod; such a flow field may inform the predator of the whereabouts of the escaping copepod prey. High Froude propulsion efficiency (0.94-0.98) was obtained for individual power stroke durations of all simulated jumps. This is unusual for small aquatic organisms but is caused by the rapidity and impulsiveness of the jump that allows only a low-cost viscous wake vortex to travel backwards.