Flow separation control by pulsed corona actuators

In this experimental work, corona actuators with triangular tips on their anodes are applied on a symmetric airfoil and tested in the wind tunnel at a freestream velocity of 20 m/s (Re = 330k). The actuators are driven by a periodic waveform that improves remarkably their operability with respect to DC driving, increasing also their efficiency. The basic waveform or carrier wave can be modulated introducing a pulsed actuation as usually done for other kinds of plasma actuators. Steady (carrier only) and pulsed (modulated) operation are tested for two actuators, selected out of a larger set previously studied in the laboratory, and compared here with a standard wire-plate corona as reference. The diagnostics include measurements of aerodynamic forces, electrical parameters and local velocities, completed by surface visualizations. Force coefficients and electrical power are used to evaluate the actuators performance in terms of coefficients changes with respect to the smooth airfoil and to the unpowered case, determini also effectiveness parameters in N/W. At the same time, the control mechanism is studied by acquiring boundary layer velocity profiles with plasma off and on, and determining the momentum coefficient of the devices. The passive effects of the unpowered actuators are measured separately and also described by means of surface visualizations. The results confirm the streamwise momentum injection as main mechanism for these actuators, and lead to determine the best flow control achievable by this technique.