Airfoil selection for a small-scale vertical axis wind turbine; a numerical study*

Airfoil selection is one of the most important criteria in the overall performance of Vertical-Axis Wind Turbines. In this paper, we present methods for the selection of an airfoil for a small-scale vertical axis wind turbine to operate at relatively low tip-speed ratios. With the application of Computational Fluid Dynamics, the aerodynamic performance of the selected airfoil is then compared to the commonly used NACA 0018 airfoil. The selection is based on the effect of the tangential force coefficient over a specific range of angles of attack. A code was developed using MATLAB software to use NACA four-digit algorithm to generate the geometry of the airfoils. Using this algorithm, over 2000 airfoil geometries were generated and analyzed. The tangential force coefficient is a lift and drag force coefficient product at a defined angle of attack. Xfoil V6.99 was implemented in the code to predict drag and force coefficients. These values are then compared to the NACA 0018 airfoil. The airfoil that yields the highest tangential force coefficient at a defined range of angles of attack is chosen. The CFD analysis shows that the power coefficient of the turbine equipped with the selected airfoil exceeds that of the one equipped with NACA 0018 for a lower rotational rate.