School of Mechanical Engineering, Purdue University, West Lafayette, IN 47906, USA.
Bioinspir Biomim. 2013 Sep;8(3):036010. doi: 10.1088/1748-3182/8/3/036010. Epub 2013 Aug 7.
The flapping wings of flying animals create complex vortex wake structure; understanding its spatial and temporal distribution is fundamental to animal flight theory. In this study, we applied the volumetric 3-component velocimetry to capture both the near- and far-field flow generated by a pair of mechanical flapping wings. For the first time, the complete three-dimensional wake structure and its evolution throughout a wing stroke were quantified and presented experimentally. The general vortex wake structure maintains a quite consistent form: vortex rings in the near field and two shear layers in the far field. Vortex rings shed periodically from the wings and are linked to each other in successive strokes. In the far field, the shed vortex rings evolve into two parallel shear layers with dominant vorticity convected from tip and root vortices. The shear layers are nearly stationary in space compared to the periodic vortex rings shed in the near field. In addition, downwash passes through the centers of the vortex rings and extends downward between the two shear layers.
飞行动物的拍打翅膀会产生复杂的涡旋尾流结构；理解其空间和时间分布对于动物飞行理论至关重要。在这项研究中，我们应用了体积式三分量速度测量法来捕捉一对机械拍动翅膀产生的近场和远场流动。首次通过实验定量描述和展示了整个三维尾流结构及其在整个翅膀挥动过程中的演化。一般的涡尾流结构保持着相当一致的形态：近场中的涡环和远场中的两个剪切层。涡环从翅膀上周期性地脱落，并在连续的挥动中相互连接。在远场中，脱落的涡环演变成两个平行的剪切层，主导的涡旋由翼尖和翼根涡旋的对流产生。与近场中周期性脱落的涡环相比，剪切层在空间上几乎是静止的。此外，下洗气流穿过涡环的中心，并在两个剪切层之间向下延伸。
