The aerodynamic performance of passive wing pitch in hovering flight
The aerodynamic performance of passive wing pitch in hovering flight
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DOI：
10.1063/5.0006902
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发表时间：
2020-05
影响因子：
4.6
通讯作者：
Menglong Lei;Chengyu Li
中科院分区：
文献类型：
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作者：
Menglong Lei;Chengyu Li
由于翅膀底部区域的扭转灵活性，昆虫的翅膀可以在每一次拍打中被动地保持大攻角，而不需要主动俯仰运动的辅助。然而，对于如何设计扭转机翼的灵活性以实现最佳的气动性能，目前还没有明确的认识。本文采用扭转弹簧模型对果蝇翅膀悬停飞行时的被动俯仰机理进行了计算研究。用气动力与结构弹性力之比柯西数来表征扭转机翼的刚度。不同的拍打模式，包括零偏差、8字形和椭圆形拍打轨迹，沿着水平划线平面进行了评估。气动力和相关的非定常流动结构使用基于室内浸没边界方法的计算流体动力学求解器进行了模拟。在雷诺数为300的情况下，对柯西数进行了参数研究。通过对气动性能的分析，发现在一定的柯西数范围内(0.15-0.30)，对于所有不同的扑翼轨迹，都可以达到大升力和高升力比的平衡。这一范围与文献中根据果蝇的实验测量计算出的柯西数是一致的。此外，还对被动扑翼产生的三维尾迹结构进行了详细分析。这项工作的发现可以为设计更高效的扑翼微型飞行器提供重要的启示。
Insect wings can passively maintain a high angle of attack during each flapping stroke without the aid of the active pitching motion due to the torsional flexibility of the wing basal region. However, there is no clear understanding of how torsional wing flexibility should be designed for achieving optimal aerodynamic performance. In this work, a computational study was conducted to investigate the passive pitching mechanism of a fruit fly wing in hovering flight using a torsional spring model. The torsional wing stiffness was characterized by the Cauchy number, a ratio between the aerodynamic force and the structural elastic force. Different flapping patterns including zero-deviation, figure-8, and oval-shaped flapping trajectories were evaluated along a horizontal stroke plane. The aerodynamic forces and associated unsteady flow structures were simulated using an in-house immersed-boundary-method based computational fluid dynamics solver. A parametric study on the Cauchy number was performed with a Reynolds number of 300. According to the analysis of the aerodynamic performance, we found that a balance of high lift and high lift-to-power ratio can be achieved in a particular range of Cauchy numbers (0.15–0.30) for all different flapping trajectories. This range is consistent with the Cauchy number calculated based on the experimental measurements of a fruit fly in the literature. In addition, 3D wake structures generated by the passive flapping wings were analyzed in detail. The findings of this work could provide important implications for designing more efficient flapping-wing micro-air vehicles.