The flow field around a freely swimming copepod in steady motion. Part I: Theoretical analysis
The flow field around a freely swimming copepod in steady motion. Part I: Theoretical analysis
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DOI：
10.1093/plankt/24.3.167
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发表时间：
2002-03-01
影响因子：
2.1
通讯作者：
Meneveau, C
中科院分区：
文献类型：
--
作者：
Jiang, HS;Osborn, TR;Meneveau, C
对自由游动的桡足类在定常运动时的三维流场进行了理论研究。本研究是基于耦合的Navier-Stokes方程与动力学方程的理想身体的桡足类。为了使流场得到解析解，进行了三个简化：（a）为了模拟头部附肢的跳动运动的影响，将力场添加到Navier-Stokes方程中;（B）为了使问题线性化，使用Stokes流;以及（c）为了简化桡足类的形态，假设球形身体形状。推导了五种定常运动的解析解：（1）悬停，（2）下沉，（3）向上游动，（4）向后游动和（5）向前游动。结果表明，自由游动的桡足类绕流场的几何形状随游动行为的不同而有显著的变化。当桡足类在水中盘旋或缓慢游动时，它会产生一个宽的锥形流场。相反，当桡足类下沉或快速游泳时，流动几何形状不是圆锥形，而是圆柱形，窄而长。这些结果是一致的发表意见活桡足类。结果表明，不同的游泳行为的流动几何形状的差异是由于在产生流场的两个因素之间的相对重要性：桡足类的游泳运动和要求，以抵消桡足类多余的重量。研究结果还强调了将自由游动的桡足类视为自推进而不是拖曳体的重要性。“自推进”意味着一个自由的，游泳的桡足类必须从周围的水获得推力，以抵消水的阻力和它多余的重量。无论游泳行为和速度，远场速度场衰减到由一个点力的大小等于桡足类的多余重量在一个无限域中产生的速度场。另一方面，使用拖曳体模型产生具有非常不同的远场和近场流特性的流场。因此，拖曳体模型本质上无法再现自由游动的桡足类周围流场的基本特征。
The three-dimensional flow field around a free-swimming copepod in steady motion was studied theoretically. This study was based on coupling the Navier-Stokes equations with the dynamic equations for an idealized body of a copepod. To allow analytical solutions to the flow field, three simplifications were made: (a) to simulate the effect of the beating movement of the cephalic appendages, a force-field was added to the Navier-Stokes equations, (b) to linearize the problem, Stokes flow was the used, and (c) to simplify morphologies of the copepods, a spherical body shape teas assumed. Analytical solutions were derived for five steady motions: (1) hovering, (2) sinking, (3) upwards swimming, (4) backwards swimming and (5) forwards swimming. The results show that the, geometry of the flow field around a freely, swimming copepod varies significantly with the different swimming behaviours. When a copepod hovers in the water or swims very slowly it generates a wide, cone-shaped flow field. In contrast, when a copepod sinks, or swims fast, the flow geometry is not cone-shaped, but cylindrical, narrow and long. These results are consistent with published observations on live copepods. It is shown that the differences in the flow geometry with the different swimming behaviours are due to the relative importance between the the two factors in generating the flow field: the copepod's swimming motion and the requirement to counterbalance the copepods excess weight. The results also highlight the importance of considering freely swimming copepods as self-propelled rather than as towed bodies. 'Self-propelled' means a freely, swimming copepod must gain thrust from the surrounding water in order to counterbalance the drag force by water and its excess weight. Regardless of swimming behaviours and velocities, the far-field velocity field decays to that of the velocity field generated by a point force of magnitude equal to the copepod's excess weight in an infinite domain. On the other hand, using the towed body model yields a flow field with much different far- and near-field-flow characteristics. Hence, the towed body model is inherently unable to reproduce fundamental characteristics of the flow field around a freely swimming copepod.