Investigation of flows over airfoils operating at low Reynolds numbers and development of effective flow control strategies.

最近在小型机械系统方面的进展，如中小型风力涡轮机和无人驾驶飞行器，引起了人们对低雷诺数空气动力学的兴趣。在这些应用中，翼型在弦雷诺数范围从约50,000到500,000，翼型的性能与传统空气动力学的预期有很大的不同。具体来说，层流边界层分离经常发生在翼型的上表面，这降低了升力，增加了阻力。分离剪切层的行为和分离流动区域的程度是决定翼型性能退化程度的主要因素。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体物理。提出的研究的主要目标是提高对低雷诺数下翼型流动发展的理解，并开发有效的主动反馈流动控制方法，以提高翼型性能。为了满足这些目标，新的实验研究将在平板上进行，受到不利的压力梯度和翼型模型，与前几何形状作为流动模型的翼型，同时促进广泛的参数调查。实验将在自适应壁风洞中进行，利用高速流动可视化，速度测量和新开发的时间分辨表面测量技术，包括嵌入式麦克风。这种原始的实验方法的组合将提供独特的见解，以流动发展在低雷诺数翼型。研究结果除了在流体力学基础上具有重要意义外，还将对实际工程应用产生重大影响。研究结果对于设计更高效的小型机械系统提升面和实施有效的流量控制策略以提高系统性能至关重要。

Recent advancements in miniaturized mechanical systems, such as small-to-medium scale wind turbines and unmanned aerial vehicles, have brought about an increased interest in low Reynolds number aerodynamics. In these applications, airfoils operate at chord Reynolds numbers ranging from about 50,000 to 500,000, and airfoil performance differs substantially from that expected in classical aerodynamics. Specifically, laminar boundary layer separation often takes place on the upper surface of the airfoil, which decreases lift and increases drag. The behaviour of the separated shear layer and the extent of a separated flow region are major factors that determine the degree of degradation in airfoil 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. The main objectives of the proposed research are to improve understanding of flow development over airfoils at low Reynolds numbers and to develop effective active-feedback flow control methods for enhancing airfoil performance. To meet these objectives, novel experimental studies will be performed on a flat-plate subjected to an adverse pressure gradient and on an airfoil model, with the former geometry serving as a model of flow over an airfoil while facilitating extensive parametric investigations. Experiments will be performed in an adaptive-wall wind tunnel utilizing high-speed flow visualization, velocity measurements, and a newly developed time-resolved surface measurement technique involving embedded microphones. This original combination of experimental methods will provide unique insight into the flow development over an airfoil at low Reynolds numbers. In addition to their significance for fundamental fluid mechanics, the research results will have a strong impact on practical engineering applications. The findings will be essential for designing more efficient lifting surfaces for miniaturized mechanical systems and implementing effective flow control strategies for improving system performance.