Flow characteristics of aerial swimmers: flapping wing propulsion of tiny insects flying at extremely low Reynolds numbers

研究复杂生物体中力产生的流体动力学过程对于深入理解飞行和游泳动物的运动是至关重要的。在过去的十年里，昆虫和鸟类产生Lift的不同寻常和强大的机制吸引了生物流体动力学领域的众多研究人员。大多数关于昆虫空气动力学的研究认为动物的翅膀很简单，大多是刚性的平板，在大约200到10,000个雷诺数之间拍打。相比之下，翼展不到一毫米的小昆虫的飞行被排除在这项分析之外，因为小昆虫完全放弃了翼型动作，真正地在空中游泳。此外，与传统昆虫和鸟类不同的是，小型昆虫表现出不同寻常的梳状平面翅膀，高达80%的翅膀表面被长毛取代。在我们对刷毛机翼对爬行流动推进的空气动力学影响的理解上存在着明显的差距，包括基于阻力的推进系统如何产生垂直升力来支撑体重的问题。因此，这项建议涉及雷诺数小于10的最小昆虫中的流体动力学现象。我们的目标是量化刷毛翅膀飞行的流动结构，利用高速视频技术对翅膀运动学进行评分，并使用时间分辨数字粒子图像测速仪(TRPIV)来量化流动结构。利用机器人机翼，我们将确定刷毛机翼设计在尾迹结构和力产生方面的功能相关性，并随后将扑动模型机翼的流动结构与飞行昆虫获得的数据进行比较。这项工作的结果可能会给我们对动物运动的几个新的见解，即通过估计微型生物飞行系统中的边界层结构和粘性阻力推进，以及通过提供飞行的空气动力学关键值，可以用来确定在高粘性环境中的功率消耗和飞行效率。

Investigating the fluid dynamic processes of force production in complex organisms is central for any in-depth understanding of locomotion in flying and swimming animals. Within the past decade, the unusual and potent mechanisms of lift production in insects and birds have attracted numerous researchers in the field of biological fluid dynamics. Most studies on insect aerodynamics considered animal wings as simple, mostly rigid, flat plates, flapping at high Reynolds numbers between approximately 200 and 10,000. Flight of small insects with wingspans of less than a millimetre, by contrast, had been excluded from this analysis because tiny insects have abandoned altogether airfoil action and literally swim in the air. In contrast to conventional insects and birds, moreover, small insects exhibit unusual wings of comb-like planform, where up to 80% of the wing surface is replaced by long hairs. There is a pronounced gap in our understanding of the aerodynamic consequences of bristle wings for creeping flow propulsion including the question of how drag-based propulsion systems may generate vertical lift for body weight support. This proposal is thus concerned with the fluid dynamic phenomenon in smallest insects flying at Reynolds numbers below approximately 10. We aim to quantify flow structures of bristle wing fliers, scoring wing kinematics by high-speed video technique and quantifying flow structures by time-resolved digital particle image velocimetry (TRPIV). Employing robotic wings, we will determine the functional relevance of bristle wing design on both wake structure and force generation, and subsequently compare flow structures at flapping model wings with the data obtained from the flying insect. The results of this work might give us several new insights into animal locomotion, i.e. by estimating boundary layer structure and viscous drag propulsion in a miniaturized biological flight system and by providing aerodynamic key values for flight that may be used to determine power expenditures and flight efficiency in highly viscous environments.