Flow Control for Wind Turbine Airfoil

The flow over a NREL S822 wind turbine airfoil was simulated for a chord Reynolds number of 100,000 and an angle of attack of 5deg. These conditions approximately match the blade element conditions at 80% radius of a 2m diameter turbine operating at 300rpm. A simulation of the uncontrolled flow with steady approach flow conditions shows boundary layer separation on the suction side which is consistent with University of Illinois at Urbana-Champaign experimental data. Active flow control has the potential to locally (and on demand) reduce the unsteady loads on individual turbine blades during non-nominal operation, thereby increasing turbine life. In addition, flow control may help lower the cut-in wind speed. Unsteady flow control for reducing the suction side separation using pulsed vortex generator jets, flip-flop jets, and plasma actuators were evaluated. It was found that very low actuation amplitudes were already sufficient for eliminating the suction side separation. The high effectiveness and efficiency is traced back to hydrodynamic instabilities that lead to a downstream growth of the forced disturbances. Too high actuator amplitudes resulted in early disturbance saturation which made the control inefficient.