On the application of active flow control to wind turbines

This paper reviews recent studies conducted at Tal-Aviv University that were aimed at applying active flow control technology to large and small scale wind turbines with the purpose of improved performance and reduced noise emission. Large wind turbines suffer from degradation of surface quality over the 20 years life span. Premature transition results and promotes early turbulent separation. Energizing the boundary layer with vortex generators (VG's) and active flow control is studied. While both methods are capable of recovering lost performance, VG's have an off-design drag penalty, while AFC can be turned off when not needed. It is demonstrated that AFC is highly energy efficient. Small wind turbines suffer from low Reynolds number effects resulting from low wind speed, small chord and low tip speed ratio. Passive and semi-active flow control methods are applied to a small vertical axis wind turbine (VAWT) with the purpose of delaying boundary layer separation via forced transition and transient semi-active fluidic jets. Power extraction at low wind speeds is demonstrated to be greatly improved.