Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA.
Bioinspir Biomim. 2013 Sep;8(3):036001. doi: 10.1088/1748-3182/8/3/036001. Epub 2013 May 17.
Direct numerical simulations are used to explore the hovering performance and efficiency for hawkmoth-inspired flapping and revolving wings at Reynolds (Re) numbers varying from 50 to 4800. This range covers the gamut from small (fruit fly size) to large (hawkmoth size) flying insects and is also relevant to the design of micro- and nano-aerial vehicles. The flapping wing configuration chosen here corresponds to a hovering hawkmoth and the model is derived from high-speed videogrammetry of this insect. The revolving wing configuration also employs the wings of the hawkmoth but these are arranged in a dual-blade configuration typical of helicopters. Flow for both of these configurations is simulated over the range of Reynolds numbers of interest and the aerodynamic performance of the two compared. The comparison of these two seemingly different configurations raises issues regarding the appropriateness of various performance metrics and even characteristic scales; these are also addressed in the current study. Finally, the difference in the performance between the two is correlated with the flow physics of the two configurations. The study indicates that viscous forces dominate the aerodynamic power expenditure of the revolving wing to a degree not observed for the flapping wing. Consequently, the lift-to-power metric of the revolving wing declines rapidly with decreasing Reynolds numbers resulting in a hovering performance that is at least a factor of 2 lower than the flapping wing at Reynolds numbers less than about 100.
直接数值模拟用于研究模仿飞蛾的扑翼和旋转翼在雷诺数（Re）从 50 到 4800 变化范围内的悬停性能和效率。这个范围涵盖了从小型（果蝇大小）到大型（飞蛾大小）飞行昆虫的范围，也与微型和纳米飞行器的设计有关。这里选择的扑翼配置对应于悬停飞蛾，模型是从这种昆虫的高速运动图像测量法中得出的。旋转翼配置也采用了飞蛾的翅膀，但这些翅膀以直升机典型的双叶片配置排列。对这两种配置的流动在感兴趣的雷诺数范围内进行了模拟，并比较了两种配置的空气动力学性能。这两种看似不同的配置的比较提出了关于各种性能指标甚至特征尺度的适当性的问题；当前的研究也解决了这些问题。最后，两种配置之间的性能差异与两种配置的流动物理有关。研究表明，旋转翼的空气动力功率消耗主要由粘性力支配，而扑翼则不然。因此，旋转翼的升力功率比随着雷诺数的降低而迅速下降，导致在雷诺数小于约 100 的情况下，悬停性能至少比扑翼低 2 倍。
