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

飞机增升减阻一直是空气动力学家和飞机设计者所追求的目标。因此，减少翼尖涡产生的升力引起的阻力，包括飞行危险，是非常重要的。安装在A320NEO和B737MAX上的鲨鱼形小翼和分体式小翼增强了升力诱导的阻力减小和随之而来的燃油消耗节约的重要性。申请人在麦吉尔大学进行了翼尖涡及其控制的深入研究（通过2009-2013年NSERC DG）。除了在低雷诺数条件下对叶顶涡的测量和表征外，还计算了基于横流速度测量的升力诱导阻力，这不仅可以评估其对总阻力的贡献，还可以表明叶顶涡流动控制的有效性（替代叶顶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，根弦长度小于主翼50%的端部非细长半三角翼（HDW）具有最大的有效抑制涡和诱导阻力的潜力。令人惊讶的是，所提出的HDW尖端涡控制也能够同时产生升力增加和失速延迟。然而，要使其实际应用，还需要进一步的研究。因此，这项拟议研究的目标有两个方面。第一部分是对目前发展前景良好的顶置HDW顶涡控制方案的继续研究。对HDW的尺寸、位置和偏转（相对于主翼）以及雷诺数进行广泛的风洞测量。这些测量将使我们能够实现一种新的实用的尖端涡控制技术。然后将从静态翼尖涡中获得的知识和发现扩展到本文的第二部分；即扑翼产生的叶尖涡的研究与控制。扑翼由于其非凡的机动性，在微型飞行器中引起了越来越多的关注。然而，与固定翼微型飞行器相比，扑翼微型飞行器更加困难，因为扑翼运动（产生升力和推力）和随之而来的流动现象非常复杂。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），类似于在振荡或俯仰机翼上形成的，最近被发现主导了非定常升力的产生。然而，LEV的形成和发展仍未完全了解。在本研究中，首先利用麦吉尔大学设计和制造的独特的多元件热膜传感器（MHFS）阵列研究了LEV（在不同扑动频率、幅值和相位下）的行为。这些表面上的MHFS和表面压力测量将用于补充扑翼尖端涡产生及其控制（例如，通过HDW尖端涡控制概念）的表面粒子图像测速测量。我们相信，这些以前无法获得的关节表面和表面外流场测量不仅可以提高我们对复杂的扑翼MAV空气动力学和推进效率的理解，还可以实现有效的扑翼尖端涡控制。所提出的实验也将为计算流体动力学验证提供一个良好的基线。

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.