Flow Control for Unsteady Aerodynamics of Pitching/Plunging Airfoils

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This project examines some generic flow control schemes for unsteady aerodynamics. In the context of this proposal unsteady aerodynamics are flow situations in which the boundary conditions exhibit time dependence. Such flows are a very common occurrence in a large number of practical applications, such as rotorcraft blades, wind turbine blades, flapping flyers or in aircraft or ground vehicles subject to turbulence and/or gusts. The proposed project considers such flows, but examines especially the possibility of introducing flow control measures, either to mitigate unwanted effects of the unsteadiness or to improve overall performance or lifetime of components. The combination of unsteady aerodynamics and flow control is a rather new research field and therefore generic configurations are chosen to explore the physics involved and the achievable control authority. In particular the leading and trailing edge vortex formation found in pitching and plunging airfoils are considered representative and suitable for such pioneering studies. The aerodynamic consequence of these vortices, which develop on the airfoil and separate after some finite growth time, can be either beneficial or detrimental, depending on application. Detrimental effects include deteriorated overall aerodynamic performance (deep stall, lift hysteresis), accelerated fatigue, or increased vibration and noise. On the other hand, vortices on an airfoil can also enhance lift, as used in insect flight and, to some extent, on helicopters. The actuators to be used in this study for flow control are the dielectric barrier discharge (DBD) plasma actuator and the synthetic jet actuator. Both are fast acting and are suitable to be integrated into either open-loop or closed-loop control strategies; hence capable of mitigating unwanted effects due to unexpected and/or unknown on-flow perturbations. The scientific goals of the project include postulating, through reference experiments and numerical simulations, the most appropriate placement and operation of the actuators, and verification of the control strategy through experiment and simulation. The outcome of the project would be an increased understanding of the control authority of the actuators and specific recommendations for implementation in real-world applications.