Active Control for Transition Delay of Two Dimensional Boundary Layers in In-Flight Experiments

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Reduction of skin friction on aircraft remains an economic and environmental issue of importance; however, active methods to achieve such reductions still require significant research and development efforts to reach industrial maturity. Even very basic questions regarding the most appropriate concept, actuator or the achievable efficiency are still open for discussion. It is within this context that the present project proposes the application of plasma actuators to invoke transition delay in two-dimensional boundary layers, in the laboratory, but especially in-flight. Previous studies have demonstrated two basic principles for achieving transition delay; a stabilization of the boundary layer, and the active wave cancellation, which have been used in four different operating modes. Many of these precursor experiments have been conducted in simple wind tunnel experiments; however also very elaborate and intricate in-flight campaigns with the institute's motorized gliders have demonstrated delay of naturally occurring transition. This very extensive preliminary work underlines the enormous potential of plasma actuators for active control on aircraft.The proposed work program intricately interweaves theoretical, numerical and experimental studies of generic configurations of flat plates and wing profiles in wind tunnels with experiments under realistic conditions on aircraft. Numerical solutions of the boundary-layer equations, together with the experimentally determined body force invoked by the plasma actuators, allow a theoretical stability analysis to assist in configuring actuator systems and arrays for energy efficient transition delay. This up-front design and optimization is then to be verified and improved using flat plate experiments in wind tunnels. Subsequent wind tunnel experiments on a full-scale wing glove can then be directly followed by in-flight experiments. Novel approaches for analyzing the power, effectiveness and induced forces of plasma actuators will then be used to evaluate the various operating modes in terms of energy balance, yielding estimates of overall efficiency. This is intended to provide a direct prognosis of how viable this application plasma actuation is in the future.