Flow control for NREL S822 wind turbine airfoil

The flow over a National Renewable Energy Laboratory S822 wind turbine airfoil was simulated for a chord Reynolds number of 100,000 and an angle of attack of 5 deg. These conditions approximately match the blade element conditions at 80% radius of a 2-m-diameter turbine operating at 300 rpm. Simulations of the uncontrolled flow show 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 nonnominal 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. Actuation frequencies of 2.5 and 5 (normalized with freestream velocity and axial chord length) and blowing velocities of 0.01, 0.1, and 1 (normalized with the freestream velocity) were investigated. It was found that blowing ratios as low as 0.1 were already sufficient for eliminating the suction side separation, resulting in a more than four times increase of the lift-to-drag ratio. The high effectiveness and efficiencyis traced back tohydrodynamic 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.