Stroke-averaged lift forces due to vortex rings and their mutual interactions for a flapping flight model
Stroke-averaged lift forces due to vortex rings and their mutual interactions for a flapping flight model
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DOI：
10.1017/s0022112010000613
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发表时间：
2010-04
影响因子：
3.7
通讯作者：
Xiaoxin Wang;Zi-niu Wu
中科院分区：
文献类型：
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作者：
Xiaoxin Wang;Zi-niu Wu
由于各种涡环及其相互作用而产生的冲程平均升力使用扑翼飞行涡模型来研究（Rayner，J. Fluid Mech.，第91卷，1979，第697页; Ellington，Phil.横河Soc. Lond. B，第305卷，1984年B，第115页）。涡系被分解为翼面涡环、边界涡和弧形尾涡闭合的环以及尾流（涡环脱落前）。使用涡量矩理论（Wu，AIAA J.，Vol.19，1981，p.432），我们能够确定涡环在升力产生或减小中的作用，并将升力表示为涡环面积收缩或膨胀的函数。尾涡环引起尾涡的面积收缩，这将降低升力，但这种降低正好被尾弧对尾涡的诱导效应所补偿。尾流通过在机翼平面上诱导下洗速度来减小升力。升力在第二半行程处下降到最小值，然后在第一半行程处增加到略低于升力的渐近值，以这种方式遵循Birch & Dickinson的实验观察（Nature，第412卷，2001，第729页）。升力负峰值的存在是由于第一个脱落涡环，它正好在后半冲程时位于机翼平面附近，导致机翼平面下洗速度的峰值。
The stroke-averaged lift forces due to various vortex rings and their mutual interactions are studied using a flapping flight vortex model (Rayner, J. Fluid Mech., vol. 91, 1979, p. 697; Ellington, Phil. Trans. R. Soc. Lond. B, vol. 305, 1984b, p. 115). The vortex system is decomposed into the wing plane (wing-linked) vortex ring, a loop closed by the bound vortex and (arc-shaped) trailing vortex and the wake (the vortex rings shed previously). Using the vorticity moment theory (Wu, AIAA J., vol. 19, 1981, p. 432) we are able to identify the roles of vortex rings in lift production or reduction and express the lift as function of areal contraction or expansion of vortex rings. The wake vortex rings induce areal contraction of the trailing vortex, which should decrease the lift, but this decrease is exactly compensated by the inducing effect of the trailing arc on the wake. The wake reduces the lift through inducing a downwash velocity on the wing plane. The lift force is shown to drop to a minimum at the second half stroke, and then increases to an asymptotic value slightly below the lift at the first half stroke, in such a way following the experimental observation of Birch & Dickinson (Nature, vol. 412, 2001, p. 729). The existence of the negative peak of lift is due to the first shed vortex ring which, just at the second half stroke, lies in the close vicinity to the wing plane, leading to a peak of the wing plane downwash velocity.