Active Flow Control of Wind Turbine Blades

Active flow control is a technique to improve the fluid dynamics of an aerodynamic body utilizing an active actuator and energy input. Much progress on the application of active flow control techniques for wind turbine blades has been accomplished in the last decade. The main focus has been on regulating unsteady aerodynamic blade loads and vibration by controlling the flow locally along the blade. The trailing edge flap and synthetic jet actuator have emerged among the most effective actuators for wind turbines. This chapter gives an overview of active flow control techniques, with a specific focus on the application and use of the piezoelectric synthetic jet for vibration reduction of small-scale wind turbine blade models tested in a wind tunnel. Using the techniques presented, the global flow field over the blade was altered such that flow separation was mitigated. Consequently, this resulted in a significant decrease in the vibration of the blade. Particle image velocimetry (PIV) was used to quantify the flow field over the blade. Using synthetic jets, the flow over the blade was either fully or partially reattached, depending on the angle of attack. Current and future research in this field has evolved to understanding and controlling realistic 3D vortex flows typical of actual wind turbines utilizing scaled-down rotor platforms. To this end, the author presents the design and operation of a rotor test tower with custom blades embedded with synthetic jet actuators aimed at investigating multi-scale blade tip vortex interaction and breakdown that may lead to blade vibration and noise reduction.