三维柔性皱褶蜻蜓翼气动效能机理研究

Dragonfly is an excellent pilot in nature, and it has always been the focus of research on the excellent aerodynamic and pleated structural properties of dragonfly wings. The micro-structures and their own passive flexibility of dragonfly wings play the important roles in flight. In the early stage of aerodynamic and structural studies, the dragonfly wings were simplified too much because of their complex structures. In this project, a precise three-dimensional flexible forewing and hindwing model will be established and we will study the aerodynamic performance and high lift mechanism of dragonfly flight by solving the N-S equation. Firstly, the aerodynamic performance of the dragonfly wings will be studied in gliding flight influenced by the micro-structure and flexibility; Secondly, during the forward flight and hovering, the leading edge of the wing will form a strong leading edge vortex(LEV), and the LEV is an important reason for the high lift mechanism, and the microstructure and flexibility of dragfly wings will influence on the structure, evolution and stably maintaining appendage characteristics of the LEV,therefore, this is a necessary work to study. Due to the interaction between the forewing and hindwng, the flapping wings may induce the various complex wakes, the wake generated by the flapping forewing will directly interfere with the flow field around the hindwing, this project will study the effects of the phase and space variation between the flapping forewing and hindwing, and discuss the interaction on the flow field around the wings, and reveal the aerodynamic performance influenced by the microstructure and flexibility, so as to achieve the better aerodynamic performance. Therefore, it has a profound significance in biology and fluid mechanics to discuss the the mechanism of flexible and microstructural effects on the dragon flight.

蜻蜓是自然界优异的飞行者，蜻蜓翼结构和气动特性机理始终是研究热点，蜻蜓翼上皱褶微结构和本身被动柔性在飞行中发挥了重要作用。前期气动和结构研究中，由于结构复杂，对蜻蜓翼做了过多的简化。本项目将建立精确三维柔性皱褶前、后翼模型，通过求解N-S方程来研究蜻蜓飞行气动效能和高升力机制。首先，研究蜻蜓滑翔时微结构和柔性对其气动效能的影响；其次，蜻蜓前飞和悬停时，蜻蜓翼前缘会形成很强的前缘涡，而前缘涡是蜻蜓产生高升力机制的重要原因，因此，微结构、柔性对蜻蜓翼前缘涡结构、演变及其稳定保持附体的特性作用成为研究蜻蜓翼的重要工作；由于前后翼之间相互作用，双翼扑动可能诱导出多种复杂尾迹，前翼扑动所产生尾迹将直接干扰后翼所处流场，研究前翼与后翼之间相位和间距变化对流场的影响规律、蜻蜓翼柔性和微结构与流场的作用规律，以获得更好的气动效能。本项目研究将在生物学和空气动力学两方面回答柔性及微结构对蜻蜓飞行作用机理。

项目围绕蜻蜓翼微结构和柔性在不同运动状态下的气动特性而展开，利用重叠网格技术与流固耦合方法，数值分析了三维扑翼模型在滑翔和前飞运动中的流体力学机理。首先提出了一种高精度的蜻蜓三维褶皱模型，探究了单独的蜻蜓前、后翼在滑翔时褶皱结构对蜻蜓翼气动效能的作用，发现蜻蜓的褶皱结构被驻留涡填充，褶皱翼型上下表面的反向驻留涡降低了蜻蜓翼的摩擦阻力，使其阻力系数与平板的阻力系数相当而升力却优于平板。褶皱上凸部分承受蜻蜓滑翔时的主要载荷，蜻蜓褶皱翼的前缘翅脉诱导出比平板更强的前缘涡，使蜻蜓的升阻比大于平板，进而诱导出更加大的气动力；其次构建了三维蜻蜓翼串列模型，分析了不同迎角不同雷诺数对蜻蜓翼的气动特性影响，分析了双翼尾涡与流场的作用规律以及翼间的干涉效应；探究了柔性对蜻蜓翼的气动干扰，柔性的存在使前翼的气动力提升约3%。被动的扭转变形会使实际来流的迎角减小，且翅翼的弯曲扭转变形会随着迎角和速度的增大而增大。最后构建了不同参数空间下的扑翼模型，研究了均匀柔性与非均匀柔性、扑动的自由度、扑动平面角等参数对前飞时推进特性和流场结构的影响。两种柔性分布方式下，柔性翼相比于刚性翼均可以显著提高前飞的推力系数。计算了不同运动方式下蜻蜓前翼的气动性能，扑动平面在合理范围内的增加有助于提高气动性能；自由度对于气动性能的影响较为复杂，且自由度中所使用的运动函数对于气动性能的影响更为复杂，其中分段函数在双自由度情况下的气动性能显著大于单自由度。本项目根据流场结构的变化解释了扑翼之间的流—固耦合作用机理，为了解昆虫、鸟类、兽（蝙蝠）类在非定常流体运动中产生的气动力作用机理具体是如何发挥作用的提供了思路，同时为研制新型仿生扑翼飞行器提供具体的理论参考。