Effect of the Reynolds number on the performance and approximate modeling of the small straight-bladed vertical-axis wind turbine

Effect of the Reynolds number on the torque and power characteristics of a small straight-bladed vertical axis wind turbine has been investigated experimentally under various wind velocity. The maximum mean torque coefficient and the maximum mean power coefficient increase with increasing the Reynolds number based on the wind velocity and representative length of the wind turbine, and the dependence of these coefficients on the Reynolds number can be successfully approximated in the logarithmic function. The tip speed ratio for the maximum mean torque coefficient is almost independent of the Reynolds number. Otherwise, the tip speed ratio for the maximum power coefficient increases as increasing Reynolds number, and the dependence of the maximum mean torque coefficient on the Reynolds number can be approximated in the logarithmic function. When the curvature parameter, the aspect ratio, and the solidity represented forms of the wind turbine are same, the wind turbine performance can be successfully explained by an semi-empirical formula including simple analytical functions, namely, the mean torque and the mean power coefficients can be represented well by the logarithmic functions of the Reynolds number and quadratic or cubic function of the tip speed ratio. The proposed approximate equations successfully predict experimental data for the particularly higher tip speed ratio.