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

飞机的增升减阻一直是空气动力学家和飞机设计者追求的目标。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上的鲨鱼小翼和分体小翼加强了升力诱导减阻和随之而来的燃料消耗节省的重要性。申请者在麦吉尔大学对翼尖涡旋及其控制进行了深入的研究(通过2009-2013年NSERC DG)。除了测量和表征低雷诺数下的叶尖涡外，还根据横流速度测量计算了升力诱导阻力，这不仅可以评估其对总阻力的贡献，还可以作为叶尖涡流控制有效性的指标(替代叶尖涡强和大小的变化)。同时，还尝试了不同的叶尖旋涡控制方法。其中，根弦小于主翼50%的尖端安装非细长半三角翼(HDW)具有最大的有效涡衰减和诱导减阻潜力。令人惊讶的是，所提出的HDW叶尖涡控制也能够产生同时的升力增量和失速延迟。然而，需要进一步的研究才能实现其实际应用。因此，这项拟议研究的目标有两个方面。第一部分是继续研究正在进行的有前景的尖端安装HDW尖端涡流控制方案。将获得HDW的大小、位置和偏转(相对于主翼)以及雷诺数的广泛风洞测量。这些措施将使我们能够实现一种新的实用的叶尖涡流控制技术。从静态机翼尖端涡流学到的知识和结论随后扩展到本提案的第二部分，即研究和控制拍打机翼产生的尖端涡流。扑翼研究因其非凡的机动性而引起了人们对微型飞行器的越来越大的兴趣。然而，与固定翼MAV相比，扑翼MAV的难度更大，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TIP效应。幸运的是，前缘涡(LEV)，类似于在摆动或俯仰机翼上形成的前缘涡，最近被发现主导了非定常升力的产生。然而，LEV的形成和生长仍然没有完全被理解。在这项研究中，首先利用McGill公司设计和制造的独特的多元热膜传感器(MHFS)阵列来研究LEV的行为(在不同的拍动频率、幅度和相位下)。这些表面MHFS和表面压力测量将用于补充扑翼尖端涡产生及其控制的离面粒子图像测速仪测量(例如，通过HDW尖端涡控制概念)。我们相信，这些以前无法获得的表面上和表面外联合流场测量不仅将促进我们对扑翼MAV复杂的空气动力学和推进效率的理解，还将使我们能够有效地控制扑翼尖端涡流。拟议的实验也将为计算流体动力学验证提供良好的基线。

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.