The Karman gait: novel body kinematics of rainbow trout swimming in a vortex street
The Karman gait: novel body kinematics of rainbow trout swimming in a vortex street
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DOI：
10.1242/jeb.00209
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发表时间：
2003-03-01
影响因子：
2.8
通讯作者：
Triantafyllou, MS
中科院分区：
文献类型：
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作者：
Liao, JC;Beal, DN;Triantafyllou, MS
大多数鱼类在其一生中通常经历不稳定的流动和水动力扰动。在这项研究中，我们提供了虹鲑鱼与环境中不是自己产生的漩涡相互作用时自愿改变其身体运动学的证据。为了证明这一点，我们测量了轴向游泳运动学，以响应已知的水动力尾迹特征的变化。我们比较了两种流速(L S(-1)为2.5和4.5时)在卡门大街不同直径柱体(2.5和5 cm)下的鲑鱼与在自由流和圆柱首尾迹中游泳的鲑鱼。鲑鱼在圆柱体后面游泳时，为了保持站位，采用了一种独特的、以前没有描述过的运动模式，我们称之为卡曼步态。在这种步态中，身体的幅度和曲率比没有圆柱体的情况下以相同的流速游泳的鲑鱼要大得多。尾拍频率不仅低于鲑鱼在圆柱体后减少的流动中游泳的预期频率，而且与圆柱体的涡旋脱落频率相匹配。因此，除了选择在圆柱体后面提供较慢的流动速度(吃水)外，鲑鱼还改变了它们的身体运动学，以与脱落的漩涡同步(调整)，使用的机制可能不涉及推进运动。当圆柱体直径相对于鱼的长度较大时，这种行为最为明显。在调谐时，鲑鱼的身体波长比规定的尾流波长更长，这表明只有身体的某些区域可能需要以一致的方式定向到迎面而来的漩涡。我们的结果表明，鱼类可以从环境产生的漩涡中捕获能量，以维持下游流动的状态。有趣的是，鲑鱼在圆柱体前游泳时，尾部跳动的幅度和体波速度比其他任何处理组的鲑鱼都要低，这意味着船头尾迹可能是鱼在圆柱体附近停留的最有利能量区域。
Most fishes commonly experience unsteady flows and hydrodynamic perturbations during their lifetime. In this study, we provide evidence that rainbow trout Oncorhynchus mykiss voluntarily alter their body kinematics when interacting with vortices present in the environment that are not self-generated. To demonstrate this, we measured axial swimming kinematics in response to changes in known hydrodynamic wake characteristics. We compared trout swimming in the Karman street behind different diameter cylinders (2.5 and 5 cm) at two flow speeds (2.5 and 4.5 L s(-1), where L is total body length) to trout swimming in the free stream and in the cylinder bow wake. Trout swimming behind cylinders adopt a distinctive, previously undescribed pattern of movement in order to hold station, which we term the Karman gait. During this gait, body amplitudes and curvatures are much larger than those of trout swimming at an equivalent flow velocity in the absence of a cylinder. Tail-beat frequency is not only lower than might be expected for a trout swimming in the reduced flow behind a cylinder, but also matches the vortex shedding frequency of the cylinder. Therefore, in addition to choosing to be in the slower flow velocity offered behind a cylinder (drafting), trout are also altering their body kinematics to synchronize with the shed vortices (tuning), using a mechanism that may not involve propulsive locomotion. This behavior is most distinctive when cylinder diameter is large relative to fish length. While tuning, trout have a longer body wavelength than the prescribed wake wavelength, indicating that only certain regions of the body may need to be oriented in a consistent manner to the oncoming vortices. Our results suggest that fish can capture energy from vortices generated by the environment to maintain station in downstream flow. Interestingly, trout swimming in front of a cylinder display lower tail-beat amplitudes and body wave speeds than trout subjected to any of the other treatments, implying that the bow wake may be the most energetically favorable region for a fish to hold station near a cylinder.