Roughness and Turbulence Effects on the Aerodynamic Efficiency of a Wind Turbine Blade Section

Abstract

Numerous experiments were conducted on a section of a 660kw wind turbine blade in a subsonic wind tunnel. The selected airfoil was tested with a clean and distributed contamination roughness surface, also with high and low tunnel turbulence intensity. Surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The surface pressure distribution is measured in the steady and unsteady condition at three Reynolds numbers, 0.43, 0.85, and 1.3 million, and over a range of angles of attack, AOA=7o-19o. Unsteady data were acquired by both pitch and plunge-type oscillation of the model about its quarter chord at a reduced frequency of 0.07. Results show that the surface roughness reduces section aerodynamic efficiency and the lift coefficient, but increases the drag coefficient for all the Reynolds numbers. The application of roughness reduces upper surface pressure coefficient and extends a separation region at high angles of attack. Increasing the tunnel turbulence intensity resulted in delay of the stall, an increase of maximum lift coefficient, and smoothness of the stall behavior. However, the drag coefficient increased significantly. Furthermore, turbulence intensity affected the predicted power output of the blade.