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

从现代涡扇发动机到风力涡轮机，再到无人驾驶/潜水器，许多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的不同。相关系统工作在低雷诺数空气动力学领域，其中层流分离导致系统性能下降。翼型几何优化和流动控制可用于延迟分离和/或最小化分离流区域的大小，从而提高升力和减少阻力。然而，实施这些方法需要深入了解流动物理，包括固有的复杂层流到湍流的过渡和非定常流动动力学。大多数先前的工作在这一领域集中在二维翼型配置在稳定的传入流。相比之下，所有相关的实际应用都涉及有限的机翼/叶片暴露于非定常来流（例如，阵风，上游物体的尾迹等）。该计划旨在弥合这一研究差距，并将当前低雷诺数空气动力学的最新技术推进到实际相关的、在稳定和非稳定流动条件下运行的有限跨度升力表面配置，从而通过设计优化和流动控制来增强系统性能。该计划的主要目标集中在三维几何形状和来流参数的时间变化对有限机翼上流动发展的影响以及对其性能的相关影响。这将通过在风洞中进行二维和有限跨度模型的新实验研究来实现，同时利用最先进的速度和力测量。采用先进的激光工具进行时间分辨和相位平均速度测量，并结合直接力测量，为流体发展和相关载荷变化提供独特的见解。这将通过速度数据的新型压力和截面负载估计来补充，以改善对跨向负载分布和动态的了解。除了它们对基础流体力学的新颖性和重要性外，所提出的研究结果将对广泛的现代和新兴应用产生强烈影响。它们将为风力涡轮机、小型螺旋桨、飞机发动机、高空平台、无人机和水下航行器设计更高效的提升面，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和开发活动。

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.