School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, United States of America.
Bioinspir Biomim. 2019 May 17;14(4):046003. doi: 10.1088/1748-3190/ab1a00.
The smallest flying insects with body lengths under 2 mm show a marked preference for wings consisting of a thin membrane with long bristles, and the use of clap and fling kinematics to augment lift at Reynolds numbers (Re) of approximately 10. Bristled wings have been shown to reduce drag forces in clap and fling, but the aerodynamic roles of several bristled wing geometric variables remain unclear. This study examines the effects of varying the ratio of membrane area (A ) to total wing area (A ) on aerodynamic forces and flow structures generated during clap and fling at Re on the order of 10. We also examine the aerodynamic consequences of scaling bristled wings to Re = 120, relevant to flight of fruit flies. We analyzed published forewing images of 25 species of thrips (Thysanoptera) and found that A /A ranged from 14% to 27%, as compared to 11% to 88% previously reported for smaller-sized fairyflies (Hymenoptera). These data were used to develop physical bristled wing models with A /A ranging from 15% to 100%, which were tested in a dynamically scaled robotic clap and fling model. At all Re, bristled wings produced slightly lower lift coefficients (C ) when compared to solid wings, but provided significant drag reduction. At Re = 10, largest values of peak lift over peak drag ratios were generated by wing models with A /A similar to thrips forewings (15% to 30%). Circulation of the leading edge vortex and trailing edge vortex decreased with decreasing A /A during clap and fling at Re = 10. Decreased chordwise circulation near the wing tip, vortex shedding, and interaction between flow structures from clap with those from fling resulted in lowering C generated via clap and fling at Re = 120 as compared to Re = 10. Clap and fling becomes less beneficial at Re = 120, regardless of the drag reduction provided by bristled wings.
最小的飞行昆虫体长在 2 毫米以下，它们明显更喜欢由薄膜和长刚毛组成的翅膀，并使用拍打和甩动运动学来增加大约 10 的雷诺数 (Re) 下的升力。已经证明，带刚毛的翅膀可以减少拍打和甩动时的阻力，但几个带刚毛的机翼几何变量的空气动力学作用仍然不清楚。本研究考察了在大约 10 的 Re 下，改变膜面积 (A ) 与总机翼面积 (A ) 的比值对拍打和甩动时产生的空气动力和流动结构的影响。我们还研究了将带刚毛的翅膀缩放到 Re = 120 的空气动力学后果，这与果蝇的飞行有关。我们分析了 25 种蓟马（缨翅目）的前翅发表的图像，发现 A /A 范围从 14%到 27%，而以前报道的较小的仙女蝇（膜翅目）的范围为 11%到 88%。这些数据用于开发 A /A 范围从 15%到 100%的物理带刚毛的机翼模型，这些模型在动态缩放的机器人拍打和甩动模型中进行了测试。在所有 Re 下，与实心机翼相比，带刚毛的机翼产生的升力系数 (C ) 略低，但提供了显著的阻力减少。在 Re = 10 时，A /A 类似于蓟马前翅（15%到 30%）的机翼模型产生的最大峰值升力与峰值阻力比。在 Re = 10 时，在拍打和甩动过程中，前缘涡和后缘涡的环量随着 A /A 的减小而减小。在机翼尖端附近翼弦向环流减小、涡脱落以及拍打和甩动产生的流动结构之间的相互作用导致与 Re = 10 相比，Re = 120 时通过拍打和甩动产生的 C 降低。无论带刚毛的翅膀提供多大的阻力减少，在 Re = 120 时，拍打和甩动的效果都会降低。
