Abstract
Active flow control systems have the potential to allow future designs of ground vehicles and aircraft to realise increased operational efficiency through improved optimisation of the flow, leading to decreased fuel use and reduced environmental impact. To achieve this, dynamic actuators are required that can adapt to the changing conditions experienced over low-speed, high-lift aerofoils where separation control can be particularly advantageous. Synthetic Jet Actuators (SJAs) are a form of the technology that shows promise; they are small, low-mass and low-power devices, which means that they can potentially realise the system efficiency a vehicular application of active flow control requires. The aims of this research were directed to achieving better understanding and robustness of the control authority from SJA systems at Reynolds Numbers close to real-world operations. The characteristics of the control authority from a round-orifice SJA array positioned near the leading-edge position of an NACA0015 aerofoil have been investigated at Re = O(10^6). Measurements demonstrated how the jet flow imparts a controlling mechanism over the separating boundary layer flow, and hence can be used to improve the overall efficiency of the wing. A series of parametric alterations to the test conditions was made in order to understand the robustness of the control effect. The forcing frequency was decoupled from the dynamic response of the actuators themselves by means of amplitude modulation. The results demonstrated that successful control could be achieved with significantly reduced input power requirements, improving net efficiency. The effectiveness was shown to be largely independent of the frequency when used in this way. Using a counterstreamwise jet orientation to control the same basic separated flow condition was not found to generate significant improvements in operational efficiency. The results suggest an in-depth understanding of the jet flow, and the excitation location in relation to the point where the flow separates is important when designing the actuators. Tests also considered a different flow condition with a stronger adverse pressure gradient, by generating a ground-effect flow over the suction surface. The control authority afforded was diminished in the more adverse flow states. The performance of the actuators was considered, and the system achieved a larger than unity Figure of Merit, indicating the overall benefit of control shows direct relevance for realising practical flow control systems. The results indicate arrays of SJA’s are capable of delivering energy savings when managing this type of flow.