Passive locomotion of a simple articulated fish-like system in the wake of an obstacle
Passive locomotion of a simple articulated fish-like system in the wake of an obstacle
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DOI：
10.1017/s0022112008002218
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发表时间：
2008-07-25
影响因子：
3.7
通讯作者：
Pisani, David
中科院分区：
文献类型：
--
作者：
Eldredge, Jeff D.;Pisani, David
本文计算研究了Re = 100时圆柱尾迹中二维刚体连接被动系统的行为。三个刚体由两个无摩擦铰链连接，系统（“鱼”）最初与圆柱体后三个直径的流向轴对齐。一旦流动对称性被打破，尾流卷起成为卡门涡街中的鱼被稳定地捕获，和通过的大尺度涡引起的波动形状变化的铰接系统。据发现，对于某些鱼的长度相对于圆柱体直径，鱼被推向上游的圆柱体。此外，当铰链被锁定时，鱼被同样有效地推进，这证实了所引起的身体波动对于实现净推力是不必要的。对各组成部分的力的分析表明，鱼前部的前缘吸力和负表面摩擦力与后部的正表面摩擦力相互竞争;当前体的贡献占后体的主导地位时，就实现了推进。结果表明，所谓的“吸力区”后面的缸，使这种被动推进是没有鱼存在的长度的两倍。
The behaviour of a passive system of two-dimensional linked rigid bodies in the wake of a circular cylinder at Re = 100 is studied computation ally. The three rigid bodies are connected by two frictionless hinges, and the system ('fish') is initially aligned with a streamwise axis three diameters behind the cylinder. Once flow symmetry is broken, the wake rolls up into a Karman vortex street in which the fish is stably trapped, and the passing large-scale vortices induce an undulatory shape change in the articulated system. It is found that, for certain fish lengths relative to cylinder diameter, the fish is propelled upstream toward the cylinder. Furthermore, the fish is propelled equally effectively when the hinges are locked, confirming that induced body undulation is not necessary for achieving a net thrust. An analysis of the forces on constituent bodies shows that leading-edge suction and negative skin friction on the forward portion of the fish are in competition with positive skin friction on the aft portion; propulsion is achieved when the forebody contributions dominate those on the aftbody. It is shown that the so-called 'suction zone' behind the cylinder that enables this passive propulsion is double the length of that without a fish present.