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Aerodynamic-force production mechanisms in hovering mosquitoes
Journal of Fluid Mechanics ( IF 3.7 ) Pub Date : 2020-07-08 , DOI: 10.1017/jfm.2020.386
Long-Gui Liu , Gang Du , Mao Sun

For many insects in hovering flight, the stroke amplitude is relatively large (above $120^{\circ }$ ) and the lift is mainly produced by the leading-edge vortex (LEV) attaching to the wing (the delayed-stall mechanism). Mosquitoes have a very small stroke amplitude ( ${\approx}45^{\circ }$ ) and the LEV does not have enough time to form before a stroke ends; thus, the delayed-stall mechanism can not be used. In the present study, we show that their lift is produced by different aerodynamic mechanisms from those of insects with a large stroke amplitude: in a downstroke and upstroke, two large lift peaks and a relatively small one are generated. The first large lift peak (at the beginning of the stroke) mainly comes from the added-mass force caused by the large acceleration of the wing. The second large lift peak (in the mid-portion of the stroke) is produced by the ‘fast-pitching-up rotation’ mechanism: the wing fast pitches up while moving forward, generating a large-magnitude, opposite-sign vorticity at the trailing edge of the wing and near the leading edge of the wing; the rapid generation of opposite-sign vorticity at different locations of the wing results in a large time rate of change in the first moment of vorticity, hence a large aerodynamic force. The third lift peak, which is near the end of the stroke and is small, is a result of the fast-pitching-up rotation of a rapidly decelerating wing. Note that although the added-mass force contributes positive lift in the beginning part of the stroke when the wing is in acceleration, it gives negative lift in the next part of the stroke when the wing is in deceleration; i.e. the added-mass force has no effect on the time-average lift, but it greatly changes the time distribution of the lift.

中文翻译:

盘旋蚊子的气动力产生机制

对于许多悬停飞行的昆虫来说,行程幅度相对较大(超过 $120^{\circ }$ ),升力主要由附着在机翼上的前缘涡(LEV)产生(延迟失速机制)。蚊子的行程幅度非常小( ${\approx}45^{\circ }$ ),并且 LEV 在行程结束之前没有足够的时间形成;因此,不能使用延迟失速机制。在本研究中,我们表明它们的升力是由与具有大行程幅度的昆虫不同的空气动力学机制产生的:在下行程和上行程中,产生两个大的升力峰值和一个相对较小的峰值。第一个大升力峰值(在行程开始时)主要来自机翼大加速度引起的附加质量力。第二个大升力峰值(在行程的中间部分)是由“快速俯仰旋转”机制产生的:机翼在向前移动的同时快速向上俯仰,在飞机上产生一个大的幅度相反的涡流。机翼后缘和机翼前缘附近;机翼不同位置的异号涡量的快速产生导致涡量第一矩的时间变化率大,从而产生大的气动力。第三个升力峰值靠近行程末端并且很小,是快速减速机翼快速俯仰旋转的结果。请注意,虽然附加质量力在机翼加速时在冲程的开始部分提供正升力,但在机翼减速时它在冲程的下一部分提供负升力;IE
更新日期:2020-07-08
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