On the measurement, characterization and control of static-wing tip vortex flow and its extension to flapping wing

增升减阻一直是空气动力学家和飞机设计师们不懈追求的目标。因此，减小翼尖涡流产生的升力诱导阻力，包括飞行危险，是非常重要的。安装在A320 NEO和B737 MAX上的鲨鱼式小翼和分裂式小翼加强了升力诱导阻力减小和随后的燃油消耗节省的重要性。申请人已在麦吉尔大学对翼尖涡流及其控制进行了深入研究（通过2009-2013 NSERC DG）。除了在低雷诺数下对叶尖涡进行测量和表征外，还根据横流速度测量值计算了升力诱导阻力，这不仅可以评估其对总阻力的贡献，而且还可以作为叶尖涡流动控制有效性的指示（替代叶尖涡强度和大小的变化）。同时，还尝试了不同的叶尖涡控制方法。其中，安装在翼尖的非细长半三角翼（HDW），根弦小于主翼的50%，被发现具有最大的潜力，有效的涡衰减和诱导阻力减少。令人惊讶的是，建议HDW叶尖涡控制也能够产生并发的升力增量和失速延迟。然而，需要进一步的调查，以实现其实际应用。 因此，这项研究的目的有两个方面。第一部分是继续研究正在进行的有前途的桨尖安装HDW桨尖涡控制方案。将获得HDW的尺寸、位置和偏转（相对于主翼）以及雷诺数的广泛风洞测量结果。这些测量将使我们能够实现一种新的和实用的叶尖涡控制技术。从静翼梢涡中得到的知识和发现，然后扩展到本建议的第二部分，即，扑翼产生的翼尖涡的研究与控制。扑翼飞行器由于其优异的机动性，引起了人们越来越多的关注。然而，与固定翼微型飞行器相比，扑翼微型飞行器由于扑翼运动（产生升力和推力）的异常复杂性和随之而来的流动现象而更加困难。此外，为了增加复杂性，必须仔细考虑尖端效应。幸运的是，前缘涡（LEV），类似于振荡或俯仰机翼上的发展，最近已被确定为主导的非定常升力的产生。然而，LEV的形成和生长仍然没有完全理解。在这项研究中，LEV的行为（在不同的扑动频率，振幅和相位）进行了研究，首先通过使用独特的多元件热膜传感器（MHFS）阵列，麦吉尔大学设计和制造。这些表面MHFS和表面压力测量将用于补充扑翼翼尖涡流产生及其控制的离表面粒子图像速度测量（例如，通过HDW尖端涡流控制概念）。我们相信，这些以前无法获得的表面和离表面联合流场测量不仅将促进我们对复杂的扑翼MAV空气动力学和推进效率的理解，而且还能实现有效的扑翼翼尖涡流控制。建议的实验也将提供一个很好的基线计算流体动力学验证。

Lift increment and drag reduction of aircraft have been persistently pursued by aerodynamicists and aircraft designers. As such, the reduction of wingtip vortices-generated lift-induced drag, including flight hazards, is therefore of great importance. The sharklet winglets and split winglets installed on A320NEO and B737MAX reinforce the significance of lift-induced drag reduction and the ensuing fuel-burn savings. Intensive study of the wingtip vortex and its control has been carried out at McGill University by the applicant (via 2009-2013 NSERC DG). In addition to the measurements and characterization of the tip vortex at low Reynolds numbers, the lift-induced drag is also computed, based on the cross-flow velocity measurements, which not only allows the evaluation of its contribution to the total drag but also serves as an indicative of the effectiveness of tip vortex flow control (alternative to the changes in the strength and size of the tip vortex). Meanwhile, different tip vortex control methods were also attempted. Among them, the tip-mounted non-slender half-delta wing (HDW), with a root chord smaller than 50% of the main wing, was found to have the greatest potential for effective vortex attenuation and induced-drag reduction. Surprising enough, the proposed HDW tip-vortex control is also capable of producing concurrent lift increment and stall delay. Further investigations are, however, needed to materialize its practical application. The objectives of this proposed research, therefore, have two folds. The first part is to continue the study of the promising on-going tip-mounted HDW tip vortex control scheme. Extensive wind-tunnel measurements of the size, location and deflection (relative to the main wing) of the HDW, and the Reynolds number will be acquired. These measurements will enable us to realize a new and practical tip vortex control technique. The knowledge and findings learned from the static-wing tip vortex is then extended to the second part of this proposal; i.e., the study and control of the tip vortex generated by flapping wings. The flapping wing study has been an increased interest in micro-air vehicles (MAVs) due to their extraordinary maneuverability. However, in comparison with fixed-wing MAVs, the flapping-wing MAVs are more difficult due to the extraordinary complexity of the flapping motions (which produce both lift and thrust) and the ensuing flow phenomena. Furthermore, to add to the complexity, tip effects must be carefully considered. Fortunately, the leading-edge vortex (LEV), similar to that developed on oscillating or pitching wings, has been identified recently to dominate the unsteady lift generation. The LEV formation and growth are, however, still not fully understood. In this study, the behavior of the LEV (under different flapping frequencies, amplitudes and phases) is studied first by using the unique multi-element hot-film sensor (MHFS) arrays, designed and fabricated at McGill. These on-surface MHFS and surface pressure measurements will be used to supplement the off-surface particle-image-velocimetry measurements of the flapping-wing tip vortex generation and its control (e.g., via the HDW tip-vortex control concept). It is our belief that these previously unavailable joint on- and off-surface flowfield measurements will not only advance our understanding of the complex flapping-wing MAV aerodynamics and propulsive efficiency, but also enable effective flapping-wing tip vortex control. The proposed experiments will also provide a good baseline for computation-fluid-dynamic validation.