IMPACT OF NUMBER OF BLADES AND SOLIDITY ON THE PERFORMANCE OF A DARRIEUS VERTICAL AXIS WIND TURBINE WITH HELICAL BLADES

The number of blades and the solidity ratio for Darrieus vertical axis wind turbines are two factors that significantly influence the performance of these wind turbines. Therefore, the objective of the current study is to investigate the impact of varying numbers of blades (2, 3, and 4 blades) as well as various solidity ratios ranging from 0.3 to 0.65 on the performance of a helical-bladed Darrieus rotor with helical angle of 90 degrees. Accordingly, the Reynolds-Average Navier-Stokes equations in three dimensions along with the turbulent model of (SST) k-omega are developed and numerically simulated. In this study, experimental results from the literature are used to validate the results predicted by the current numerical model. Thus, numerical predictions of the variations of the coefficient of power versus tip speed ratio can be made. Predicted results revealed that the coefficients of power are higher for the helical-bladed Darrieus rotor with three blades at higher ranges of tip speed ratios with respect to rotors with two and four blades. The peak coefficient of power significantly increases with raising the solidity ratio up to an optimal value 0.5, then a deterioration in peak coefficient of power is attained by a further increment of solidity ratio beyond this value. The helical Darrieus rotor with three blades and solidity ratio of 0.5 attains the highest peak coefficient of power of 0.338. Helical Darrieus rotors have a wide range of tip speed ratios at which high power coefficients can be achieved when the solidity is lower. Furthermore, as rotor solidity increases, the optimal tip speed ratio of the helical Darrieus rotor tends to decrease.