Numerical investigation of unsteady aerodynamics of a Horizontal-axis wind turbine under yawed flow conditions

Abstract

In the present study, unsteady flow features and the blade aerodynamic loading of the National Renewable Energy Laboratory phase VI wind turbine rotor, under yawed flow conditions, were numerically investigated by using a three-dimensional incompressible flow solver based on unstructured overset meshes. The effect of turbulence, including laminar-turbulent transition, was accounted for by using a correlation-based transition turbulence model. The calculations were made for an upwind configuration at wind speeds of 7, 10 and 15m/sec when the turbine rotor was at 30 degrees and 60 degrees yaw angles. The results were compared with measurements in terms of the blade surface pressure and the normal and tangential forces at selected blade radial locations. It was found that under the yawed flow conditions, the blade aerodynamic loading is significantly reduced. Also, because of the wind velocity component aligned tangent to the rotor disk plane, the periodic fluctuation of blade loading is obtained with lower magnitudes at the advancing blade side and higher magnitudes at the retreating side. This tendency is further magnified as the yaw angle becomes larger. At 7m/sec wind speed, the sectional angle of attack is relatively small, and the flow remains mostly attached to the blade surface. At 10m/sec wind speed, leading-edge flow separation and strong radial flow are observed at the inboard portion of the retreating blade. As the wind speed is further increased, the flow separation and the radial flow become more pronounced. It was demonstrated that these highly unsteady three-dimensional aerodynamic features are well-captured by the present method. Copyright (c) 2012 John Wiley & Sons, Ltd.