Data from: The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body-size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning PIV technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.

带中心体的旋转机翼中，前缘涡（leading-edge vortex，LEV）的稳定附着对高升力的生成发挥着关键作用。中心体尺寸主要通过两种途径对前缘涡结构产生显著影响：其一，中心体尺寸的整体变化会改变雷诺数（Reynolds number），而雷诺数对前缘涡结构的影响已被广泛证实；其二，中心体尺寸会根据机翼相对于旋转轴的偏移量，改变作用于机翼的科里奥利加速度（Coriolis acceleration）。为探究该问题，本研究针对旋转机翼，分别开展了雷诺数与机翼偏移量（wing-offset）的影响实验。研究采用扫描式粒子图像测速（scanning PIV）技术对三维前缘涡结构进行了流场测绘，并对图像的快速采集流程及其相关性分析进行了严格的验证。本文呈现的实验结果表明，前缘涡结构主要随雷诺数发生变化。研究发现，在小偏移量范围内（该范围恰好覆盖多数昆虫的飞行工况），改变中心体半径对前缘涡分裂（LEV-split）的影响极小；但当偏移量超出该小范围时，前缘涡分裂现象会发生显著改变。