Department of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL, United Kingdom.
Aerospace Engineering Department, Faculty of Engineering, Cairo University, Giza 12613, Egypt.
Bioinspir Biomim. 2022 Oct 27;17(6). doi: 10.1088/1748-3190/ac98e5.
A wing generating lift leaves behind a region of disturbed air in the form of a wake. For a hovering insect, the wings must return through the wake produced by the previous half-stroke and this can have significant effects on the aerodynamic performance. This paper numerically investigates 2D wings interacting with their own wake at Reynolds numbers of 10and 10, enabling an improved understanding of the underlying physics of the 'wake capture' aerodynamic mechanism of insect flight. We adopt a simple kinematic motion pattern comprised of a translational stroke motion followed by a complete stop to expose wake interaction effects. Representative stroke distance to chord ratios between 1.5 and 6.0 are considered, enabling different leading-edge vortex (LEV) attachment states. We also allow pitching rotation towards the end of stroke, leading to wake intercepting angles of 135°, 90°, and 45°, analogous to delayed, symmetric, and advanced pitching rotations of insect wings. It is shown that both vortex suction and jet flow impingement mechanisms can lead to either positive or negative effects depending on the LEV attachment state, and that stroke distances resulting in a detached/attached LEV lead to beneficial/detrimental wake interaction lift. Pitching rotation at the end of the stroke motion is found to induce a strong rotational trailing-edge vortex (RTEV). For advanced pitching, this RTEV serves to enable either a stronger flow impingement effect leading to positive wake interaction lift if the LEV is detached, or a less favourable vortex suction effect leading to negative wake interaction lift if the LEV is closely attached. The higher Reynolds number led to faster development of the wake vortices, but the primary wake interaction mechanisms remained the same for both Reynolds numbers.
一个产生升力的机翼在其身后会留下一个紊乱空气区域，即尾流。对于悬停的昆虫来说，它的翅膀必须穿过前半拍产生的尾流，这对空气动力性能会产生显著影响。本文在雷诺数为 10 和 10 的情况下，对 2D 机翼与自身尾流的相互作用进行了数值研究，这使我们能够更好地理解昆虫飞行的“尾流捕获”空气动力机制的基础物理学。我们采用了一种简单的运动模式，由平移冲程运动和完全停止组成，以暴露尾流相互作用的影响。考虑了代表冲程距离和弦长比为 1.5 到 6.0 的比值，使前缘涡（LEV）的附着状态不同。我们还允许在冲程结束时进行俯仰旋转，从而产生 135°、90°和 45°的尾流拦截角，类似于昆虫翅膀的延迟、对称和超前俯仰旋转。结果表明，涡吸和射流冲击两种机制都可能产生积极或消极的影响，这取决于 LEV 的附着状态，并且导致分离/附着 LEV 的冲程距离会导致有益/有害的尾流相互作用升力。研究发现，在冲程运动结束时进行俯仰旋转会产生强烈的尾流旋转后缘涡（RTEV）。对于超前俯仰，这种 RTEV 可以通过两种方式发挥作用：如果 LEV 分离，射流冲击效应更强，从而产生积极的尾流相互作用升力；如果 LEV 紧密附着，那么较弱的涡吸效应会导致负面的尾流相互作用升力。较高的雷诺数导致尾流涡的发展更快，但对于两种雷诺数，主要的尾流相互作用机制仍然相同。
