Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China.
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
J Exp Biol. 2018 Oct 4;221(Pt 19):jeb171199. doi: 10.1242/jeb.171199.
We investigated the characteristics of interwing aerodynamic interactions across the span of the high aspect ratio, flexible wings of dragonflies under tethered and free-flying conditions. This revealed that the effects of the interactions on the hindwings vary across four spanwise regions. (i) Close to the wing root, a trailing-edge vortex (TEV) is formed by each stroke, while the formation of a leading-edge vortex (LEV) is limited by the short translational distance of the hindwing and suppressed by the forewing-induced flow. (ii) In the region away from the wing root but not quite up to midspan, the formation of the hindwing LEV is influenced by that of the forewing LEV. This vortex synergy can increase the circulation of the hindwing LEV in the corresponding cross-section by 22% versus that of the hindwing in isolation. (iii) In the region about half-way between the wing root and wing tip there is a transition dominated by downwash from the forewing resulting in flow attached to the hindwing. (iv) A LEV is developed in the remaining, outer region of the wing at the end of a stroke when the hindwing captures the vortex shed by the forewing. The interaction effects depend not only on the wing phasing but also on the flapping offset and flight direction. The aerodynamics of the hindwings vary substantially from the wing root to the wing tip. For a given phasing, this spanwise variation in the aerodynamics can be exploited in the design of artificial wings to achieve greater agility and higher efficiency.
我们研究了高展弦比、柔性蜻蜓翅膀在系留和自由飞行条件下跨翼展的翼间空气动力学相互作用的特性。结果表明，相互作用对后翼的影响在四个展向区域上有所不同。（i）在靠近翼根处，每个冲程都会形成一个后缘涡（TEV），而前缘涡（LEV）的形成受到后翼短距离平移的限制，并被前翼诱导流抑制。（ii）在远离翼根但不到翼展中部的区域，后翼 LEV 的形成受到前翼 LEV 的影响。这种涡协同作用可以使相应截面后翼 LEV 的环流增加 22%，而与孤立后翼相比。（iii）在翼根和翼尖之间大约一半的区域，由于前翼的下洗，流场附着在后翼上，主导着过渡。（iv）当后翼捕获前翼释放的涡时，在一个冲程的最后，在翼的剩余外部区域形成一个 LEV。相互作用的影响不仅取决于翼相位，还取决于扑动偏移和飞行方向。后翼的空气动力学特性从翼根到翼尖有很大的变化。对于给定的相位，这种展向变化的空气动力学特性可以在人工翅膀的设计中得到利用，以实现更高的敏捷性和更高的效率。
