变翼展的仿生扑翼尾迹特征

Wake of a bio-inspired flapping wing with morphing wingspan

本文基于仿生扑翼流动的数值模拟研究变形翼展对尾迹结构的影响.所采用的扑翼模型为一个在均匀来流中上下扑动的平板.翼展随着扑动而变化,最大翼展在下扑行程的中间,最小翼展在上挥行程的中间.其尾迹的特征表现为两条相互连接的倾斜涡链.虽然变形翼展对尾流拓扑结构的影响不大,但它显著影响了扑翼附近涡结构,导致尾流中涡环链的分布不对称.下扑过程中,位于扑翼下表面的前缘涡收缩,与上挥中翼尖涡相互作用,通过分析升力系数,发现上述涡的相互作用是由翼展长度的变化引起的.

This work uses a bio-inspired flapping wing model to numerically investigate the effect of morphing wingspan on wake structures.The model consists of a rectangular flat-plate wing heaving harmonically in a uniform incoming flow at the Reynolds number of 300 and Strouhal number of 0.3.The wingspan changes during heaving,with a maximum wingspan at the middle of downstroke and minimum wingspan at the middle of upstroke.The wake is characterized by two oblique chains of interconnected vortex loops.Although the morphing wingspan has little effect on the wake topology,it significantly affects the magnitude and size of the vortices near the wing surface,which leads to an asymmetric distribution of vortex loop chains in the wake.The shrinking of leading-edge vortex under the lower surface of the wing in downstroke and the destructive interaction of tip vortices in upstroke are identified as the two vortex dynamics corresponding to the asymmetric wake structures.The analysis on the lift coefficients shows that the above vortex interactions are mainly caused by the change of span length instead of spanwise velocity.