Effect of Steady and Quasi-Unsteady Wind on Aerodynamic Performance of H-Rotor Vertical Axis Wind Turbines

Abstract

Many researchers have studied different horizontal-axis and vertical-axis wind turbines (VAWTs) by conducting the experimental and numerical simulations. However, the vertical-axis wind turbine has currently attracted attention because of its simpler geometry and lower manufacturing costs compared with the horizontal-axis wind turbine. This study investigates the effects of steady and quasi-unsteady upstream winds on the aerodynamic performance of vertical axis wind turbines with a symmetric (NACA 4415) and an asymmetric (RISØ-A1-24) airfoil using the double multiple stream tube (DMST) method. To verify the developed MATLAB code, the experimental results of tangential force are compared with the present result for the NACA 12 airfoil. The results also are compared with another numerical simulation using the same method (DMST) for the NACA 4415 airfoil, which shows good agreement for all comparisons. In order to generate the quasi-unsteady wind, although some past simulations have used computational fluid dynamics (CFD) and experimental approaches, this study applies a new approach using a random function with a turbulence intensity of 2% and a random wind with a wide range of frequencies. The main aim of this research is to study the effect of steady and quasi-unsteady wind on a symmetric and an asymmetric airfoil as well as the capability of the DMST method to predict quasi-unsteady loads. According to the results, both symmetric and asymmetric airfoils result in similar power coefficients. Furthermore, comparison of the results in steady and quasi-unsteady flow shows that the highest amplitude of the fluctuation occurs when each blade passes an azimuth angle of −4° to 4°. Results of this study reveal the capability of the DMST method to predict quasi-unsteady results due to unsteady wind. Therefore, predicting the aerodynamic performance of VAWT using wind inputs that represent the typical turbulence spectrum is feasible.