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Aerodynamic force and vortex structures of flapping flexible hawkmoth-like wings

机译:扑翼状类似鹰蛾翅膀的气动力和涡流结构

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Aerodynamic characteristics were determined and flow visualizations were carried out in order to interpret the effects of wing flexibility for hawkmoth-like wings on aerodynamic force generation. The flexibility varied according to wing thickness: Case 1 used a 3-mm thick rigid wing, while Cases 2, 3, and 4 used 0.8-, 0.5-, and 0.35-mm thick flexible wings, respectively. The wings were constrained to a sinusoidal flapping motion in a water tank, and digital particle image velocimetry captured three sections of each wing model by fixing the position of the laser, shooting at 30%, 50%, and 70% of the rigid wing length. The flexible wings had phase delays in the stroke motion, which had influence on vortex generation, particularly the leading-edge vortex (LEV). As the wing became flexible, the vorticity of the LEV and the corresponded lift decreased. However, Case 2 had greater aerodynamic force than other cases due to the behavior of the new LEV after the wing reversal. In particular, the new LEV around the wingtip was delayed in its dispersal due to part of the LEV generated during the previous stroke. The encounter between the new LEV and the LEV residue induced the flow over the leading edge, preventing the new LEV dispersal. Along with the higher stroke velocity after a specific time, the delayed LEV dispersal helped the flexible wing have higher lift. Cases 3 and 4, on the other hand, showed large wing deformations during flapping, which caused the vortex structures around the flapping wing to become relatively unstable. Accordingly, they had much less aerodynamic force than the previous cases. These results help to explain how flexible wings obtain more or less aerodynamic force, and they also suggest the importance of setting a specific range of flexibility to enable greater aerodynamic force for insect-inspired flapping micro aerial vehicles (MAVs). (C) 2016 Elsevier Masson SAS. All rights reserved.
机译:确定了空气动力学特性并进行了流动可视化分析,以解释鹰蛾类机翼的机翼柔性对气动力产生的影响。柔韧性随机翼厚度的不同而变化:案例1使用3毫米厚的刚性机翼,而案例2、3和4分别使用0.8毫米,0.5毫米和0.35毫米厚的柔性机翼。机翼在水箱中被约束成正弦拍打运动,数字粒子图像测速仪通过固定激光的位置捕获了每个机翼模型的三个部分,以刚性机翼长度的30%,50%和70%进行拍摄。柔性机翼在冲程运动中具有相位延迟,这会影响涡旋的产生,尤其是前沿涡旋(LEV)。随着机翼变得灵活,LEV的涡度和相应的升力降低。但是,由于机翼反转后新LEV的行为,案例2具有比其他案例更大的空气动力。特别是,由于前一冲程产生的LEV的一部分,翼尖周围的新LEV的扩散被延迟了。新的LEV和LEV残留物之间的相遇导致了流过前沿,从而阻止了新的LEV扩散。在特定时间后,随着较高的冲程速度,延迟的LEV扩散有助于柔性机翼具有更高的升力。另一方面,情况3和4在拍打过程中显示出较大的机翼变形,这导致拍打翼周围的涡旋结构变得相对不稳定。因此,它们比以前的情况具有更少的空气动力。这些结果有助于解释挠性机翼如何获得或多或少的空气动力,并且它们还建议设置特定范围的挠性以使昆虫启发的拍打微型飞行器(MAV)具有更大的空气动力的重要性。 (C)2016 Elsevier Masson SAS。版权所有。

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