Numerical investigation of the hydrodynamics of carangiform swimming in the transitional and inertial flow regimes
Numerical investigation of the hydrodynamics of carangiform swimming in the transitional and inertial flow regimes
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DOI：
10.1242/jeb.015644
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发表时间：
2008-05-15
影响因子：
2.8
通讯作者：
Sotiropoulos, Fotis
中科院分区：
文献类型：
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作者：
Borazjani, Iman;Sotiropoulos, Fotis
我们采用数值模拟来研究carangiform运动的流体动力学的粘性和惯性力的相对大小，即雷诺数（Re），和尾拍频率，即斯特劳哈尔数（St），是系统地变化。该模型鱼是一个三维（3D）鲭鱼一样的灵活的身体波动规定的实验运动学carangiform类型。模拟进行了三个Re跨越过渡和惯性流制度，Re=300和4000（粘性流），和无穷大（无粘流）。对于每一个Re，都有一个临界的斯特劳哈尔数St*，在这个数下，净平均力变为零，使得恒速自推进成为可能。St* 是Re的递减函数，只有当Re接近无穷大时，St才接近大多数Carangiform游泳者在自然界游泳时的St范围（St类似于0.25）。在St* 处的推进效率是Re的递增函数，而游泳所需的功率随着Re而减小。然而，对于所有的Re，游泳的力量被证明是显着大于所需的拖曳刚体以相同的速度。我们还表明，总阻力的变化，其粘性和形状组件与St依赖于Re。当Re=300时，物体起伏使阻力增加，而当Re=4000时，阻力显著减小。这种差异被证明是由于这样的事实，即在足够高的Re的阻力与St的变化是由它的形状组成部分的变化，这是减少了波动游泳的St>0.2。最后，我们的模拟澄清了实验中观察到的各种尾流模式的三维结构-单排和双排涡-并表明尾流结构主要取决于St。我们的数值研究结果有助于阐明以前的活鱼实验结果，强调尺度（Re）对Carangiform游泳水动力性能的重要性，并有助于解释为什么在自然界中这种游泳模式通常是快速游泳者的首选。
We employ numerical simulation to investigate the hydrodynamics of carangiform locomotion as the relative magnitude of viscous and inertial forces, i.e. the Reynolds number (Re), and the tail-beat frequency, i.e. the Strouhal number (St), are systematically varied. The model fish is a three-dimensional (3D) mackerel-like flexible body undulating with prescribed experimental kinematics of carangiform type. Simulations are carried out for three Re spanning the transitional and inertial flow regimes, Re=300 and 4000 (viscous flow), and infinity (inviscid flow). For each Re there is a critical Strouhal number, St*, at which the net mean force becomes zero, making constant-speed self-propulsion possible. St* is a decreasing function of Re and approaches the range of St at which most carangiform swimmers swim in nature (St similar to 0.25) only as Re approaches infinity. The propulsive efficiency at St* is an increasing function of Re while the power required for swimming is decreasing with Re. For all Re, however, the swimming power is shown to be significantly greater than that required to tow the rigid body at the same speed. We also show that the variation of the total drag and its viscous and form components with St depend on the Re. For Re=300, body undulations increase the drag over the rigid body level, while significant drag reduction is observed for Re=4000. This difference is shown to be due to the fact that at sufficiently high Re the drag force variation with St is dominated by its form component variation, which is reduced by undulatory swimming for St>0.2. Finally, our simulations clarify the 3D structure of various wake patterns observed in experiments - single and double row vortices - and suggest that the wake structure depends primarily on the St. Our numerical findings help elucidate the results of previous experiments with live fish, underscore the importance of scale (Re) effects on the hydrodynamic performance of carangiform swimming, and help explain why in nature this mode of swimming is typically preferred by fast swimmers.