Distributed flexibility in inertial swimmers
Distributed flexibility in inertial swimmers
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DOI：
10.1017/jfm.2020.49
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发表时间：
2020-04-10
影响因子：
3.7
通讯作者：
Rowley, Clarence W.
中科院分区：
文献类型：
--
作者：
Floryan, Daniel;Rowley, Clarence W.
我们研究了具有分布式灵活性的被动柔性游泳者的线性无粘模型，计算其推进性能和最佳的灵活性分布。我们考虑的驱动频率和平均刚度比范围很大，而质量比固定为代表游泳者的较低值。我们提供的结果显示了后缘偏转、推力系数、功率系数和效率如何随频率、平均刚度和刚度分布变化。具有分布式灵活性的游泳者与具有均匀灵活性的游泳者具有相同的质量特征。然而，通过调整刚度以触发共振响应，或者如果无法触发共振，则可以通过将刚度集中到前缘来获得推力的显着增益。为了最小化功率，反之亦然。通过将刚度集中在远离前缘的位置，可以在低频下显着提高效率，因为这样做会产生有效的行波运动学。我们还推测有限雷诺数对流向阻力的影响。阻力增加了游泳者产生的净推力的抵消，导致灵活性的效率最大化分布倾向于推力最大化分布，这代表了自然界中发现的情况。
We study a linear inviscid model of a passively flexible swimmer with distributed flexibility, calculating its propulsive performance and optimal distributions of flexibility. The frequencies of actuation and mean stiffness ratios we consider span a large range, while the mass ratio is fixed to a low value representative of swimmers. We present results showing how the trailing edge deflection, thrust coefficient, power coefficient and efficiency vary with frequency, mean stiffness and stiffness distribution. Swimmers with distributed flexibility have the same qualitative features as those with uniform flexibility. Significant gains in thrust can be made, however, by tuning the stiffness such that a resonant response is triggered, or by concentrating stiffness towards the leading edge if resonance cannot be triggered. To minimize power, the opposite is true. Meaningful gains in efficiency can be made at low frequencies by concentrating stiffness away from the leading edge, since doing so induces efficient travelling wave kinematics. We also speculate on the effects of a finite Reynolds number in the form of streamwise drag. The drag adds an offset to the net thrust produced by the swimmer, causing efficiency-maximizing distributions of flexibility to tend towards thrust-maximizing ones, representative of what is found in nature.