Numerical Analysis on Viscous Friction Distribution over Blades and Arms of Straight-Bladed Vertical Axis Wind Turbine

Abstract

For investigating the effects of horizontal arms (cross sections: airfoil, rectangle, circle) on a straight blade vertical axis wind turbine, surface shear stress distributions and integrated friction drag were analyzed based on the CFD (Computational Fluid Dynamics) results. Since the flow separated from the corners of the leading edge side of a rectangular arm and made a counter-flow region, the wall shear stress worked as a propulsion force for the rectangular arm. The integrated friction drags were one tenth as small as the integrated pressure-based drags that were reported before. It was found that the tendency of power coefficient Cp of the wind turbine (the Cp of rectangular arm rotor < the Cp of cylindrical arm rotor) cannot be explained by the friction drag.