Functional morphology and virtual models: Physical constraints on the design of oscillating wings, fins, legs, and feet at intermediate Reynolds numbers
Functional morphology and virtual models: Physical constraints on the design of oscillating wings, fins, legs, and feet at intermediate Reynolds numbers
复制标题
DOI：
10.1093/icb/42.2.232
复制
发表时间：
2002-04-01
影响因子：
2.6
通讯作者：
Walker, JA
中科院分区：
文献类型：
--
作者：
Walker, JA
为什么有些动物通过前后摆动附肢来游泳，而另一些动物则通过上下拍打附肢来飞行？一种假说认为，答案与小而慢的动物和大而快的动物所遇到的截然不同的物理环境有关。拍打的附肢使大型动物能够快速有效地在流体环境中移动。然而，随着尺寸和速度的减小，粘性阻力越来越占主导地位的力量平衡，与划船和扑翼附肢的负面影响。然而，比较数据表明，拍动不会发生在动物在雷诺数（Re）小于约15.1使用计算机模拟实验来解决这个问题，“低于什么Re划船比拍动更有效？“模拟采用了虚拟振荡附件的简单准定常叶片单元模型，有几个重要结果。首先，划船和扑翼的机械效率随着规模的增加而急剧下降。第二，划船的性能可以通过利用几个动态形状修改，包括在恢复冲程期间的面积和跨度减小而显著增加。最后，划船和扑翼的相对性能取决于前进比，前进比是相对于振荡频率的行进速度的函数。该模型预测，对于在通常观察到的前进比范围内移动的动物，在Re < 20时划船比拍打更有效。
Why do some animals swim by rowing appendages back and forth while others fly by flapping them up and down? One hypothesis suggests the answer ties in the sharply divergent physical environments encountered by small, slow animals, and large, fast animals. Flapping appendages allow large animals to move through a fluid environment quickly and efficiently. As size and speed decrease, however, viscous drag increasingly dominates the force balance, with negative consequences for both rowing and flapping appendages. Nevertheless, comparative data suggest that flapping does not occur in animals at Reynolds numbers (Re) less than about 15.1 used a computer simulation experiment to address the question, "Below what Re is rowing more effective than flapping?" The simulation, which employed a simple quasi-steady, blade-element model of virtual oscillating appendages, has several important results. First, the mechanical efficiency of both rowing and flapping decrease dramatically with scale. Second, the performance of rowing can increase substantially by taking advantage of several dynamic shape modifications, including area and span reduction during the recovery stroke. Finally, the relative performance of rowing and flapping is dependent on the advance ratio, which is a function of the travel speed relative to the oscillation frequency. The model predicts that rowing is more efficient than flapping at Re < 20 for animals moving throughout the range of typically observed advance ratios.