The effect of rotation on the boundary layer of a wind turbine blade

Abstract

Design and analysis methods for wind turbines are presently based on relatively simple models of rotor blade aerodynamics, such as 2-D blade element/momentum theory (BEMT). Field investigations over the past few years have shown discrepancies between predicted and measured performance, owing to the effect of rotation on the wind turbine blade boundary layer distribution. The present paper is aimed at describing a fundamental phenomenon: the effect of rotation on the blade boundary layer of a wind turbine. In this paper, 3-D incompressible steady momentum integral boundary layer equations are employed to study this complex problem. By solving the 3-D integral boundary layer equations with the assumed velocity profiles and a closure model (including both laminar and turbulent boundary layer models), the effects of rotation on blade boundary layers are investigated. Several key parameters, such as separation position and momentum thickness, are calculated and compared for the rotation and non-rotation cases. It is concluded that the stall is postponed due to rotation and the separation point is delayed as a result of increasing rotation speed or decreasing blade spanwise position. Possible modifications that should be considered to the existing 2-D BEMT method are suggested.