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

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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.