Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.
Wake development behind paired wings with tip and root trailing vortices: consequences for animal flight force estimates.
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DOI：
10.1371/journal.pone.0091040
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发表时间：
2014
期刊：
影响因子：
3.7
通讯作者：
Bomphrey RJ
中科院分区：
文献类型：
--
作者：
Horstmann JT;Henningsson P;Thomas AL;Bomphrey RJ
最近在动物身上进行的扑翼飞行实验表明，许多不相关的物种在左右翅膀后面都会产生由尖涡和根涡组成的尾流。在这里，我们提出了一个调查，使用粒子图像测速（PIV）的行为和相互作用的尾随涡脱落的配对，固定的翅膀，简化和模仿后的飞行动物与非升力体。我们测量了两个相邻NACA 0012翼型下游五个位置的流速，并系统地改变展弦比、机翼之间的差距（对应于非升力体的宽度）、攻角和雷诺数。长宽比和雷诺数的范围被选择为与自然飞行者和游泳者，特别是昆虫飞行有关。我们发现，作为诱导流分布的结果，成对机翼后面的尾流变形，使得翼尖涡向下对流，而根部涡相互扭曲。涡流相互作用和尾流变形在机翼的下游变得更加明显，因此，在飞行动物实验中，PIV测量平面的位置对随后的力估计有重要影响，因为旋转诱导流矢量。尾流变形是最严重的翅膀后，与较低的长宽比，当翅膀之间的距离很小，这表明符合这种描述的动物构成高风险组的测量误差。因此，我们的研究结果，有显着的影响，实验设计中使用的尾流测量来估计动物飞行中产生的力。特别是，测量平面的下游距离应最小化，尽管在测量飞行动物后面的尾流时存在动物福利限制。
Recent experiments on flapping flight in animals have shown that a variety of unrelated species shed a wake behind left and right wings consisting of both tip and root vortices. Here we present an investigation using Particle Image Velocimetry (PIV) of the behaviour and interaction of trailing vortices shed by paired, fixed wings that simplify and mimic the wake of a flying animal with a non-lifting body. We measured flow velocities at five positions downstream of two adjacent NACA 0012 aerofoils and systematically varied aspect ratio, the gap between the wings (corresponding to the width of a non-lifting body), angle of attack, and the Reynolds number. The range of aspect ratios and Reynolds number where chosen to be relevant to natural fliers and swimmers, and insect flight in particular. We show that the wake behind the paired wings deformed as a consequence of the induced flow distribution such that the wingtip vortices convected downwards while the root vortices twist around each other. Vortex interaction and wake deformation became more pronounced further downstream of the wing, so the positioning of PIV measurement planes in experiments on flying animals has an important effect on subsequent force estimates due to rotating induced flow vectors. Wake deformation was most severe behind wings with lower aspect ratios and when the distance between the wings was small, suggesting that animals that match this description constitute high-risk groups in terms of measurement error. Our results, therefore, have significant implications for experimental design where wake measurements are used to estimate forces generated in animal flight. In particular, the downstream distance of the measurement plane should be minimised, notwithstanding the animal welfare constraints when measuring the wake behind flying animals.
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