Inboard/outboard plasma actuation on a vertical-axis wind turbine

Vertical axis wind turbine (VAWT) blades can experience large positive and large negative angles-of-attack that produce both inboard and outboard dynamic stall. Dielectric barrier discharge (DBD) plasma actuators can control dynamic stall and hence an inboard/outboard switching control technique was developed where encapsulated electrodes were deployed on either side of the blades of an H-rotor turbine. An electromechanical system, including a shaft-mounted micro-switch and high-voltage relays, was developed for the purpose of earthing the inboard encapsulated electrode of the upwind blade with the outboard encapsulated electrode of the downwind blade. The actuators were connected to a high-voltage source via slip-rings and were pulse-modulated to exploit flow instabilities in an on/off feed-forward configuration. Turbine performance measurements showed that switching produced slightly larger improvements than either inboard or outboard actuation alone. The modest differences were traced to weak plasma being generated over the floating encapsulated electrodes, whose source was unavoidable slip-ring conductor proximity. Elimination of the floating electrode plasma resulted in larger performance increments for inboard versus outboard actuation due to the larger dynamic pressure relative to the blades in the upwind swept area of the turbine compared to that in the the downwind swept area.