论文标题
在维护附带的前沿涡流中通过模型鸟alula
On the maintenance of an attached leading-edge vortex via model bird alula
论文作者
论文摘要
研究人员假设，鸟类羽毛或阿鲁拉的后台提升益处源于维持附着的前缘涡流（LEV），其薄薄的外翼。在这里，我们通过风隧道中的流量测量结果研究了尚拉拉和LEV附着之间的联系。我们表明，一个模型的蓝菌（Model Alula）的润湿面积是翼的1％，它稳定在稳定翻译的无扫描的无扫地机翼上，稳定了循环的尾倾斜LEV。附着的涡旋是尚拉拉（Alula）平稳合并其他单独的前沿和侧边涡流流的结果。我们确定了有助于合并的两个关键过程：i）在机翼的前缘回到机翼平面上产生的跨度涡度的转向，ii）高质量的根到尖端跨度流动的后置壁式隔离（> 80％的自由速度速度）。后一个功能引起了LEV的卷起，而前者的特征则倾斜了LEV涡旋，并通过舷外涡度通量将这种流向机翼尖端的流动。我们将蓝藻的流向位置（相对于薄机翼的前沿）确定对于涡流转向和蓝色的CANT角度对于高稳定的跨度流量的重要性很重要。这些发现提高了我们对Bird杠杆利用LEV的可能方式增强缓慢飞行的理解。
Researchers have hypothesized that the post-stall lift benefit of bird's alular feathers, or alula, stems from the maintenance of an attached leading-edge vortex (LEV) over their thin-profiled, outer hand-wing. Here, we investigate the connection between the alula and LEV attachment via flow measurements in a wind tunnel. We show that a model alula, whose wetted area is 1% that of the wing, stabilizes a recirculatory aft-tilted LEV on a steadily-translating unswept wing inclined at post-stall incidences. The attached vortex is the result of the alula's ability to smoothly merge otherwise separate leading- and side-edge vortical flows. We identify two key processes that facilitate this merging: i) the steering of spanwise vorticity generated at the wing's leading edge back to the wing plane and ii) an aft-located wall-jet of high-magnitude root-to-tip spanwise flow (>80% that of the freestream velocity). The latter feature induces LEV roll-up while the former feature tilts LEV vorticity aft and evacuates this flow toward the wing tip via an outboard vorticity flux. We identify the alula's streamwise position (relative to the leading-edge of the thin wing) as important for vortex steering and the alula's cant angle as important for high-magnitude spanwise flow generation. These findings advance our understanding of the likely ways bird's leverage LEVs to augment slow flight.
