Lifting surfaces in low Reynolds number flows: bridging the gap between laboratory research and practice

从现代涡轮风扇发动机到风力涡轮机，再到无人驾驶航空器/潜水器，许多新技术和新兴技术的空气动力学性能与经典空气动力学的预测有很大不同。相关系统在低雷诺数空气动力学领域中操作，其中层流分离导致系统性能的劣化。翼型几何优化和流动控制可用于延迟分离和/或最小化分离流动区域的尺寸，从而增强升力并减小阻力。然而，实施这些方法需要深入的知识，涉及固有的复杂的层流到湍流过渡和非定常流动动力学的流动物理。这一领域的大多数先前工作集中在定常来流中的二维翼型构型上。相反，所有相关的实际应用都涉及暴露于非定常来流的有限机翼/叶片（例如，阵风、来自上游物体的尾流等）。拟议的计划旨在弥合这一研究差距，并将低雷诺数空气动力学的当前最新技术推进到实际相关的有限翼展升力面配置，在定常和非定常流条件下运行，从而通过设计优化和流量控制提高系统性能。 所提出的计划的主要目标集中在三维几何形状和时间变化的影响，在来流参数的流动发展有限的机翼和相关的影响，其性能。这将通过在风洞中对二维和有限跨度模型进行新颖的实验研究来实现，同时利用最先进的速度和力测量。利用先进的激光工具进行的时间分辨和相位平均速度测量将与直接力测量相结合，以提供对流动发展和相关载荷变化的独特见解。这将通过新的压力和截面载荷估算来补充，以提高对展向载荷分布和动力学的了解。除了它们的新奇和对基础流体力学的意义外，拟议研究的结果将对广泛的现代和新兴应用产生强烈影响。它们将能够为风力涡轮机、小型螺旋桨、飞机发动机、高空平台、无人驾驶航空器和水下航行器设计更有效的升力面，并设计和实施有效的流量控制策略，以进一步提高性能。该计划还将促进研究生的培训，他们将支持相关的知识转移和进一步的研究与开发活动。

The aerodynamic performance of many new and emerging technologies, ranging from modern turbofan engines to wind turbines to unmanned aerial/submersible vehicles, differs substantially from the predictions of classical aerodynamics. The relevant systems operate in the domain of low Reynolds number aerodynamics, where laminar flow separation leads to a degradation in system performance. Airfoil geometry optimization and flow control can be used to delay separation and/or to minimize the size of the separated flow region, thereby enhancing lift and decreasing drag. However, implementing these methods requires in-depth knowledge of the flow physics involving inherently complex laminar-to-turbulent transition and unsteady flow dynamics. Most prior work in this domain focused on two-dimensional airfoil configurations in steady incoming flows. In contrast, all relevant practical applications involve finite wings/blades exposed to unsteady incoming flows (e.g., wind gusts, wakes from upstream objects, etc.). The proposed program aims to bridge this research gap and advance the current state-of-the-art in low Reynolds number aerodynamics to practically relevant, finite-span lifting surface configurations operating in both steady and unsteady flow conditions, thereby enabling enhancement of system performance through design optimization and flow control. The main objectives of the proposed program focus on the effects of the three-dimensional geometry and temporal variations in the incoming flow parameters on the flow development over finite wings and the associated impact on their performance. This will be achieved by conducting novel experimental studies on both two-dimensional and finite-span models in a wind tunnel utilizing simultaneous state-of-the-art velocity and force measurements. Time-resolved and phase-averaged velocity measurements with advanced laser-based tools will be coupled with direct force measurements to provide unique insights into the flow development and the associated changes in loading. This will be complemented by novel pressure and sectional load estimations from the velocity data for improved insight into spanwise load distributions and dynamics. In addition to their novelty and significance for fundamental fluid mechanics, the results of the proposed research will have a strong impact on a wide range of modern and emerging applications. They will enable the design of more efficient lifting surfaces for wind turbines, small-scale propellers, aircraft engines, high-altitude platforms, unmanned aerial and underwater vehicles, as well as designing and implementing effective flow control strategies for further performance improvements. The program will also facilitate training of graduate students who will support the associated knowledge transfer and further research and development activities.