Mechanical and Aerospace Engineering Department, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.
J Exp Biol. 2012 Feb 15;215(Pt 4):671-84. doi: 10.1242/jeb.063016.
In this work we study the hydrodynamics of a bluegill sunfish performing a C-start maneuver in unprecedented detail using 3-D numerical simulations guided by previous laboratory experiments with live fish. The 3-D fish body geometry and kinematics are reconstructed from the experiments using high-speed video and prescribed as input to the numerical simulation. The calculated instantaneous flow fields at various stages of the C-start maneuver are compared with the two-dimensional particle image velocimetry measurements, and are shown to capture essentially all flow features observed in the measurements with good quantitative accuracy; the simulations reveal the experimentally observed three primary jet flow patterns whose momentum time series are in very good agreement with the measured flow field. The simulations elucidate for the first time the complex 3-D structure of the wake during C-starts, revealing an intricate vortical structure consisting of multiple connected vortex loops at the end of the C-start. We also find that the force calculated based on the 3-D flow field has higher magnitudes than that implied by the jet momentum on the midplane, and it exhibits large and rapid fluctuations during the two stages of the C-start. These fluctuations are physical and are related to the change in the direction of the acceleration of the fish body, which changes the location of the high and low pressure pockets around the fish.
在这项工作中，我们使用三维数值模拟，以前期带有活鱼的实验室实验为指导，以前所未有的细节研究蓝鳃太阳鱼在 C 型起动机动中的流体动力学。使用高速视频从实验中重建 3-D 鱼体几何形状和运动学，并将其规定为数值模拟的输入。将 C 型起动机动各个阶段的计算瞬时流场与二维粒子图像测速测量结果进行比较，结果表明模拟能够很好地捕捉到测量中观察到的所有流动特征，具有良好的定量准确性；模拟揭示了实验中观察到的三个主要射流流动模式，其动量时间序列与测量的流场非常吻合。模拟首次阐明了 C 型起动过程中尾部的复杂 3-D 结构，揭示了在 C 型起动结束时由多个连接的涡环组成的错综复杂的涡结构。我们还发现，基于 3-D 流场计算的力比中平面射流动量所暗示的力大得多，并且在 C 型起动的两个阶段都表现出大而快速的波动。这些波动是物理性的，与鱼体加速度方向的变化有关，这会改变鱼体周围高低压口袋的位置。
