The velocity field over a two-dimensional wing at Reynolds number of 672,000 was investigated to characterize the three-dimensional topology and evolution of the separate flow with variation of the angle of attack. Planar particle image velocimetry over the full span of the wing demonstrated that with increasing angle of attack, isolated pockets of backflow, which appeared near the trailing edge, merged and formed an asymmetric stall cell at angle of attack of 9.7°. The asymmetry was mainly associated with the dissimilar boundary layers developed on the wind tunnel walls at the spanwise ends of the wing. Secondary structures were also observed between the stall cell and the spanwise end. The stall cell topology was characterized using large-scale three-dimensional particle tracking velocimetry measurements using helium-filled soap bubbles. The results showed that the separation bubble had a small wall-normal height with two wall-normal counter-rotating vortices extended up to the edge of the separation bubble. In addition, the investigations demonstrated that vortex generators can induce a symmetric stall cell by removing the secondary structures and isolating the stall cell from the flows at the spanwise ends.

研究了雷诺数为 672,000 的二维机翼上的速度场，以表征三维拓扑结构和独立流动随攻角变化的演变。机翼整个跨度上的平面粒子图像测速表明，随着迎角的增加，出现在后缘附近的孤立回流袋合并并形成了一个不对称的失速单元，迎角为 9.7°。这种不对称性主要与机翼展向端风洞壁上形成的不同边界层有关。在失速单元和展向端之间也观察到了二级结构。失速单元拓扑结构的特点是使用充满氦气的肥皂泡进行大规模三维粒子跟踪测速测量。结果表明，分离泡的壁法向高度较小，两个壁法向反向旋转涡旋延伸至分离泡的边缘。此外，研究表明涡流发生器可以通过去除二级结构并将失速单元与展向端的流动隔离来诱导对称失速单元。