Dynamic Stall Control on a Vertical Axis Wind Turbine Using Plasma Actuators
Dynamic stall was controlled on the blades of a small high-solidity vertical axis wind turbine, by means of dielectric barrier discharge plasma actuators installed on the blade leading-edges. A parametric study was conducted with the objective of increasing the net power output resulting from control in an open-loop manner. For the majority of experiments, the actuators were configured to control separation on the upwind half of the turbine azimuth while limited experiments were conducted on the downwind half. Turbine power was measured using a specially-designed dynamometer that allowed full characterization of its performance. Actuator duty cycle dependence observed previously on static airfoils was also observed on the turbine. However, optimum reduced frequencies showed substantially different dependence and this was traced to the importance of the plasma pulsation frequency relative to the turbine rotational frequency. Overall turbine power performance improvements of 38% and 20% were measured for upwind and downwind dynamic stall control, respectively. Based on the data acquired, up-scaling the turbine by a factor of 5 and 10, the percentage of plasma power required to produce comparable improvements was conservatively estimated at 3.3% and 1.7% respectively. A new switching-direction actuator was developed, together with high-speed plasma triggering, in order to produce combined upwind and downwind actuation that is phase-locked to turbine rotational frequencies. Flowfield measurements using particle image velocimetry are presently being performed.