Passive aeroelastic deflection of avian primary feathers
Passive aeroelastic deflection of avian primary feathers
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DOI：
10.1088/1748-3190/ab97fd
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发表时间：
2020-05
影响因子：
3.4
通讯作者：
B. Klaassen van Oorschot;R. Choroszucha;B. Tobalske
中科院分区：
文献类型：
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作者：
B. Klaassen van Oorschot;R. Choroszucha;B. Tobalske
鸟类羽毛是复杂的结构，在与空气相互作用时被动偏转以产生空气动力。牛顿理论表明，羽毛应该是坚硬的，才能有效地利用这种力。对飞行鸟类的观察表明，羽毛通过翼展方向的弯曲、扭转和扫掠来响应空气动力载荷。假设这些偏转可以优化飞行性能，但这尚未经过测试。我们在风洞中测量了孤立羽毛的偏转，以探索灵活性如何改变模拟滑翔飞行中的空气动力。使用七只猛禽的主要羽毛和刚性机翼，我们量化了弯曲、扫掠和扭曲，以及 α（迎角）和滑移角。我们预测：（1）羽毛在空气动力载荷下会偏转，（2）弯曲会导致力的横向重定向，（3）扭曲会改变展向α“冲刷”并延迟失速的发生，（4）羽毛的弯曲刚度将表现出正异速生长。我们的结果支持前三个预测，但第四个则不然。我们发现，弯曲导致侧向力更偏向羽毛底部，大约为总升力的 10%。与在 α = 13.5° 处失速的翼型相比，随着攻角增加到我们测量范围的极限（α = 27.5°），所有羽毛都继续增加升力产生。我们观察到羽毛刚度表现出正异速生长（∝mass1.1±0.3），但是这一发现与其他假设的尺度关系（例如几何相似性（∝mass1.67））在统计上没有差异。这些结果表明，羽毛柔韧性可以通过扭转减少羽毛尖端的局部α来提供被动滚动稳定性和延迟失速。我们的研究结果首次测量了空气动力载荷下羽毛偏转所产生的力，并且可以为未来的鸟类飞行模型以及仿生变形翼技术提供信息。
Bird feathers are complex structures that passively deflect as they interact with air to produce aerodynamic force. Newtonian theory suggests that feathers should be stiff to effectively utilize this force. Observations of flying birds indicate that feathers respond to aerodynamic loading via spanwise bending, twisting, and sweeping. These deflections are hypothesized to optimize flight performance, but this has not yet been tested. We measured deflection of isolated feathers in a wind tunnel to explore how flexibility altered aerodynamic forces in emulated gliding flight. Using primary feathers from seven raptors and a rigid airfoil, we quantified bending, sweep, and twisting, as well as α (attack angle) and slip angle. We predicted that (1) feathers would deflect under aerodynamic load, (2) bending would result in lateral redirection of force, (3) twisting would alter spanwise α ‘washout’ and delay the onset of stall, and (4) flexural stiffness of feathers would exhibit positive allometry. The first three predictions were supported by our results, but not the fourth. We found that bending resulted in the redirection of lateral forces more toward the base of the feather on the order of ∼10% of total lift. In comparison to the airfoil which stalled at α = 13.5°, all feathers continued to increase lift production with increasing angle of attack to the limit of our range of measurements (α = 27.5°). We observed that feather stiffness exhibited positive allometry (∝ mass1.1±0.3), however this finding is not statistically different from other hypothesized scaling relationships such as geometric similarity (∝ mass1.67). These results demonstrate that feather flexibility may provide passive roll stability and delay stall by twisting to reduce local α at the feather tip. Our findings are the first to measure forces due to feather deflection under aerodynamic loading and can inform future models of avian flight as well as biomimetic morphing-wing technology.