Department of Mechanical and Materials Engineering, Queen's University, Kingston, ON, K7L 3N6, Canada.
Bioinspir Biomim. 2017 Jun 20;12(4):046007. doi: 10.1088/1748-3190/aa6f47.
The dynamics of a simple perching manoeuvre are investigated using circular and aspect-ratio-two elliptical flat plates, as abstractions of low-aspect-ratio planforms observed in highly-manoeuvrable birds. The perching kinematic investigated in this study involves a pitch-up motion from an angle of attack of [Formula: see text] to [Formula: see text], while simultaneously decelerating. This motion is defined by the shape change number, [Formula: see text], which acts as a measure of the relative contributions of added-mass and circulatory effects. This motion has been observed in natural flyers during controlled landings, and has recently been explored through the use of a nominally two-dimensional airfoil. The parameter space of low-aspect-ratio plates therefore serves to elucidate how realistic free-end conditions affect the timescales of vortex evolution, and therefore the relative contributions between added mass and circulation. The results presented herein suggest that for the low-aspect-ratio plates, the shedding of vortices occurs more rapidly than for equivalent two-dimensional cases, and therefore faster pitching motions are required to compensate for the lower levels of lift and drag. Furthermore, the vortex topology and instantaneous forces that arise during the rapid-area changes show no sensitivity to aspect ratio, and strong collapse is observed between both flat plates. Similar aerodynamic advantages may therefore be exploited during perching manoeuvres by birds of various scale regardless of wing aspect ratio.
使用圆形和纵横比为 2 的椭圆形平板来研究简单栖息动作的动力学，这些平板是在高度机动的鸟类中观察到的低纵横比翼型的抽象。本研究中研究的栖息运动涉及从攻角[Formula: see text]到[Formula: see text]的俯仰运动，同时减速。这种运动由形状变化数[Formula: see text]定义，它是附加质量和循环效应相对贡献的度量。在自然飞行中已经观察到这种运动在受控着陆期间，并且最近通过使用名义上的二维翼型进行了探索。因此，低纵横比板的参数空间有助于阐明真实自由端条件如何影响涡旋演化的时间尺度，从而影响附加质量和循环之间的相对贡献。本文的结果表明，对于低纵横比板，涡旋的脱落比等效二维情况快，因此需要更快的俯仰运动来补偿较低的升力和阻力。此外，在快速面积变化期间出现的涡旋拓扑和瞬时力对纵横比没有敏感性，并且在两个平板之间观察到强烈的崩溃。因此，无论翼型纵横比如何，各种规模的鸟类在进行栖息动作时都可能利用类似的空气动力优势。
