Zheng Yingying, Wu Yanhua, Tang Hui
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798, Singapore.
Bioinspir Biomim. 2015 Feb 6;10(1):016021. doi: 10.1088/1748-3190/10/1/016021.
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°, 90° and 180°. 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 1 Hz (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°, 90° and 180° 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.
在悬停飞行以及斯特劳哈尔数分别为0.6和0.3的两次前飞中，测量了经历联合下扑/俯仰运动的柔性和刚性串联翼的气动力、功率消耗和效率。三种类似蜻蜓的柔性串联翼模型，分别称为翼I、翼II和翼III，其柔性逐渐降低，以及一对刚性翼作为参考，在0°、90°和180°三个相位差下运行。结果表明，柔性和相位差对气动性能都有显著影响。在1 Hz（St = 0.6）的较高振荡频率下的悬停和前飞中，翼III模型的总水平力系数和效率更大，优于其他翼模型。在0.5 Hz（St = 0.3）的较低频率下的前飞中，翼III、刚性翼和翼II模型分别在0°（相位差）、90°（相位差）和180°（相位差）时表现最佳。从前翼和后翼的力系数随时间变化曲线可以发现，不同的峰值、相位滞后和二次峰值是导致平均水平力系数存在差异的重要原因。进行了粒子图像测速和变形测量，以深入了解柔性如何影响串联翼的气动性能。发现翼展方向的弯曲变形有助于产生水平力，在悬停和前飞中，它通过提供一个更有利的位置，使前缘涡更附着在翼模型上，并在前飞中诱导出一个高速区域。
