The boundary layer in the hub area of wind turbine blades at high wind speeds

At low tip speed ratios, the strongest effect at the inboard half-span, when a vortex like flow occurs, is produced. These 3-D rotational effects contribute to a stall delay as well as higher lift and angles of attack at the inboard sections, as compared to 2-D flow conditions. A greater understanding of the mechanisms and properties of the shear layer close to the upper side surface of blade is sought through the development of an analytic theory and then is completed by CFD computations. The results show that the secondary flow has a slip effect on the blade surface and its circumferential velocity is less than that of blade revolution, particularly important for TSR <3.0. While at the high tip speed ratios the flow around the blade is much as the 2-D one, then at the low tip speed ratios, TSR < 3.0 the flow behaves rather like the impinging flow on a rotating disc. Therefore, the 3-D rotational effects dominate the flow at high wind speeds and a special approach of such flows would be to assume. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)