带前缘突节水下滑翔机机翼升阻力和流动分离控制特性实验研究

Although the size of the humpback whales is huge, they are capable of performing complex underwater maneuvers. Recent research shows that this has been attributed to their pectoral flippers, where several tubercles are distributed along the leading-edge. These leading-edge tubercles act as vortex generators, which can enhance the lift and reduce the drag. In fact, this passive flow control technique by using leading-edge tubercles can be applied on the hydrodynamic lifting surfaces of the ocean engineering devices. The underwater glider always works with lower velocities, and the hydrofoils in the corresponding lower Reynolds numbers flow are prone to flow separation, which can lead to poor performance of the hydrofoils. This project aims to improve the hydrodynamic performance for the hydrofoils for the underwater gliders through the passive flow control technique of leading-edge tubercles..Based on the similarity principle in fluid dynamics, the present project will be conducted in a low speed close-circuit wind tunnel. By using force balance, time-resolved particle image velocimetry (TR-PIV) and flow visualization techniques, this project will investigate:.• Effects of static pitch angles, dynamic pitch, roll and yaw, tubercle configurations, Reynolds numbers, airfoils and wing profiles on the hydrodynamic characteristics, as well as vortices shedding characteristics in the shear layer and flow separation region;.• Mechanism of the periodic flow separation for tubercled wings tested under static flow conditions;.• Effect of the leading-edge tubercles on the formation and evolution of the dynamic stall vortex for the tubercled wings tested under dynamic flow condition..Through this project, a tubercled wing configuration design for the underwater glider with the optimum hydrodynamic performance and better flow separation control behaviour will be presented.

座头鲸虽然体型庞大但仍灵活敏捷，研究表明其非凡的运动能力和其胸鳍前缘上分布的突节有关，这些突节类似于涡发生器，具有增升减阻等作用。事实上，前缘突节流动被动控制方法也可应用在海洋工程装备的水动力学控制面上。水下滑翔机的滑翔速度通常很低，此时低雷诺数来流将会引起水翼严重的流体分离，从而降低其水动力学性能。本项目将通过此前缘突节来改善滑翔机水翼的升阻力性能。.项目利用雷诺数相似原理，通过低速风洞测力天平、高速时间解析粒子图像测速法和流动显示等技术，将研究：.• 静态俯仰角、动态俯仰、偏航和横滚运动、突节形态、雷诺数、翼型和机翼形状等，对水翼升阻力性能以及剪切层和背风区涡脱落特性的影响；.• 静态条件下，周期性流体分离的形成机理；.• 动态条件下，前缘突节对动态失速涡形成与发展的影响。.项目将提出一种水下滑翔机机翼的建议设计方案，使其具有较优的水动力性能和流动分离控制特性。

座头鲸属于海洋里卓越的捕食者。海洋生物学家发现座头鲸虽然体型庞大但仍可以做出非常灵活的动作，尤其在捕食的时候，例如高速俯冲，倾斜盘旋，甚至跃出水面空翻，如图1(a)所示。研究表明，座头鲸非凡的运动能力可能取决于其胸鳍前缘上分布的一系列突节，这些突节类似于涡发生器，具有流动分离控制作用。水下滑翔机的巡航速度通常很低，大约在0.5m/s以下，有限展长机翼对应的雷诺数也很低。在低雷诺数情况下, 滑翔机的水翼控制面会面临很严重的流动分离。此时，失速攻角变低，升力降低而阻力增加，从而导致水翼水动力学效率降低。..本项目通过数值模拟结合风洞实验测试开展的主要研究工作和研究内容包括：.1..设计了三维滑翔机和机翼的模型，翼型基于SD7032和NACA634021。.2..并利用数控机床对这些机翼进行了加工。.3..在低速风洞利用三自由度天平对三维模型和二维模型进行了测试，得到了三维滑翔机模型的升阻力特性；分析了不同带前缘突节机翼在低雷诺数环境下的动态失速特性；.4..利用表面油流显示法对三维滑翔机模型进行了研究，研究了流动分离特性。.5..低雷诺数环境下，前缘突节对水下滑翔机机翼的流动控制特性和升阻比的影响；.6..绕前缘突节对转涡相互作用机理，以及对升阻力的影响特性。..在研究过程中得到的重要研究成果主要包括两条：.1..揭示了绕前缘突节的对转涡会相互作用，相互作用的结果会影响绕机翼的瞬态流动分离，使得流动分离表现出非稳态特性，分离区域随时间而变化；.2..在低雷诺数情况下，前缘突节会显著提高水下滑翔机机翼的升力和升阻比，升阻比提高月10%，有望提高水下滑翔机的航程。.. 基于以上研究成果，本项目发表权威SCI论文4篇，在国际出版社出版专著章节一篇。主要论文和书籍成果如下：.Zhaoyu Wei, New T H, Lian L, et al. Ocean Engineering, 2019, 181: 173-184..Zhaoyu Wei, Toh, J. W. A., Ibrahim, I. H., & Zhang, Y. (2019). European Journal of Mechanics-B/Fluids, 75, 143-152..Wei, Zhaoyu, Lian Lian, and Yisen Zhong. Experiments in Flui