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Force measurements of flexible tandem wings in hovering and forward flights

机译：悬停和向前飞行中柔性串联翼的力测量

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摘要

Aerodynamic forces, power consumptions and efficiencies of flexible and rigid tandem wings undergoing combined plunging/pitching motion were measured in a hovering flight and two forward flights with Strouhal numbers of 0.6 and 0.3. Three flexible dragonfly-like tandem wing models termed Wing I, Wing II, and Wing III which are progressively less flexible, as well as a pair of rigid wings as the reference were operated at three phase differences of 0 degrees, 90 degrees and 180 degrees. The results showed that both the flexibility and phase difference have significant effects on the aerodynamic performances. In both hovering and forward flights at a higher oscillation frequency of 1Hz (St = 0.6), the Wing III model outperformed the other wing models with larger total horizontal force coefficient and efficiency. In forward flight at the lower frequency of 0.5 Hz (St = 0.3), Wing III, rigid wings and Wing II models performed best at 0 degrees, 90 degrees and 180 degrees phase difference, respectively. From the time histories of force coefficients of fore- and hind-wings, different peak values, phase lags, and secondary peaks were found to be the important reasons to cause the differences in the average horizontal force coefficients. Particle image velocimetry and deformation measurements were performed to provide the insights into how the flexibility affects the aerodynamic performance of the tandem wings. The spanwise bending deformation was found to contribute to the horizontal force, by offering a more beneficial position to make LEV more attached to the wing model in both hovering and forward flights, and inducing a higher-velocity region in forward flight.
机译：在一个悬停飞行和两个斯特劳哈尔数分别为0.6和0.3的前向飞行中，测量了经受组合的俯冲/俯仰运动的柔性和刚性串联机翼的空气动力，功率消耗和效率。三种渐弱的柔性类蜻蜓串联翼模型，称为Wing I，Wing II和Wing III，以及一对刚性翼作为参考，在0度，90度和180度这三个相位差下运行。结果表明，柔韧性和相差均对空气动力性能有重要影响。在1Hz的较高振荡频率（St = 0.6）的悬停和前向飞行中，Wing III模型的总水平力系数和效率均优于其他机翼模型。在较低的0.5 Hz（St = 0.3）频率下进行前向飞行时，机翼III，刚性机翼和机翼II分别在0度，90度和180度相位差下表现最佳。从前翼和后翼的力系数的时间历史来看，发现不同的峰值，相位滞后和次要峰是造成平均水平力系数差异的重要原因。进行了颗粒图像测速和变形测量，以提供有关柔性如何影响串联机翼空气动力学性能的见解。发现翼展方向的弯曲变形通过提供一个更有利的位置来使LEV在悬停和前向飞行中更贴近机翼模型，并在前向飞行中诱导出较高的速度区域，从而有助于水平力。

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