|M.Sc Student||Lautman Ronen|
|Subject||Combined Upwind/Downwind Plasma-Based Flow Control on a|
Vertical-Axis Wind Turbine
|Department||Department of Mechanical Engineering||Supervisor||PROF. David Greenblatt|
|Full Thesis text|
Dynamic stall poses one of the biggest problems facing the development and implementation of vertical axis wind turbines (VAWTs). Controlling this unique phenomenon poses several challenges. Since the blades experience both positive and negative angles of attack, stall occurs alternately on both sides of the blades. The resulting unsteady loads imposed on the drive-train and generator are primarily responsible for failures in the field. To control dynamic stall, a novel feed-forward control mechanism was designed and integrated with high-voltage, pulsed, dielectric barrier discharge (DBD) plasma actuators on a double-bladed VAWT. The actuators are pulsed to exploit flow instabilities in an on/off feed-forward configuration. The significant innovation accomplished during this research was the use of a novel switching system which allowed stall to be controlled on alternating actuators during continuous operation of the VAWT. A mechanical switch controlled a relay which switched between the earthed electrodes of the DBD plasma actuators which were placed on opposite sides of the VAWT blades. This enabled the high-voltage electrodes to generate plasma on alternating sides of the blades depending on which side was predicted to stall. Four types of tests were performed: actuation tests to find the output possible under different actuation conditions; tests to find the effective azimuth range of actuator operation; transient tests to characterize the system's response; and tests to quantify friction in the system. Actuation tests were performed to quantify the turbine's power output normalized by freestream wind conditions. Turbine performance was measured under different actuation conditions. Results show that actuator operation on the inboard side of the blades increased the turbine's power output more than actuator operation on the outboard side of the blades. Continuously switching actuator operation to the side predicted to stall increased power output still more. In order to minimize the power input to the actuators it is prudent to find the minimum range of azimuth positions that would effectively control stall. Tests were done to find this range and results show that actuator operation is most effective in the ranges of 21° < α < 39° and -43° < α < -27°. The transient response of the system was characterized under different actuation conditions. The time constant was found to be limited to the range of 7.6 s < τ <11.6 s. The torque due to friction in the system was measured to be 4.65 x 10-2 N•m.