Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 105 S. Mathews Ave., Urbana, IL 61801, United States of America.
Author to whom correspondence should be addressed.
Bioinspir Biomim. 2019 Aug 29;14(5):056015. doi: 10.1088/1748-3190/ab36ad.
Birds fly in dynamic flight conditions while maintaining aerodynamic efficiency. This agility is in part due to specialized feather systems that function as flow control devices during adverse conditions such as high-angle of attack maneuvers. In this paper, we present an engineered three-dimensional leading-edge device inspired by one of these specialized groups of feathers known as the alula. Wind tunnel results show that, similar to the biological alula, the leading-edge alula-inspired device (LEAD) increases the wing's ability to maintain higher pressure gradients by modifying the near-wall flow. It also generates tip vortices that modify the turbulence on the upper-surface of the wing, delaying flow separation. The effect of the LEAD location and morphology on lift production and wake velocity profile are investigated using force and hot-wire anemometer measurements, respectively. Results show lift improvements up to 32% and 37% under post and deep stall conditions, respectively. Despite the observed drag penalties of up to 39%, the aerodynamic efficiency, defined as the lift-to-drag ratio, is maintained and sometimes improved with the addition of the LEAD to a wing. This is to be expected as the LEAD is a post-stall device, suitable for high angles of attack maneuvers, where maintaining lift production is more critical than drag reduction. The LEAD also accelerates the flow over the wing and reduces the wake velocity deficit, indicating attenuated flow separation. This work presents a detailed experimental investigation of an engineered three dimensional leading-edge device that combines the functionality of traditional two dimensional slats and vortex generators. Such a device can be used to not only extend the flight envelope of unmanned aerial vehicles (UAVs), but to also study the role and function of the biological alula.
鸟类在动态飞行条件下保持空气动力学效率。这种灵活性部分归因于专门的羽毛系统，这些系统在高攻角机动等不利条件下充当流控装置。在本文中，我们提出了一种受称为翼梢小翼的特殊羽毛群之一启发的工程三维前缘装置。风洞结果表明，类似于生物翼梢小翼，前缘翼梢小翼启发式装置 (LEAD) 通过改变近壁流来提高机翼保持更高压力梯度的能力。它还会产生翼尖涡，从而改变机翼上表面的湍流，延迟流动分离。使用测力和热线风速仪测量分别研究了 LEAD 位置和形态对升力产生和尾流速度剖面的影响。结果表明，在失速后和深度失速条件下，升力分别提高了 32%和 37%。尽管观察到高达 39%的阻力损失，但由于 LEAD 是一种失速后装置，适用于高攻角机动，因此保持升力产生比减少阻力更为关键，因此添加 LEAD 到机翼上时，空气动力学效率（定义为升力与阻力比）得以维持，有时甚至会提高。LEAD 还会加速机翼上方的流动并减少尾流速度不足，表明流动分离得到缓解。这项工作对一种工程三维前缘装置进行了详细的实验研究，该装置结合了传统二维缝翼和涡流发生器的功能。这种装置不仅可以扩展无人机 (UAV) 的飞行包线，还可以研究生物翼梢小翼的作用和功能。
