Numerical analysis of the influence of number of blades on the power performance of vertical axis wind turbines

The current study systematically analyzes the impact of number of blades (n) on the aerodynamic performance of 2-, 3- and 4-bladed Darrieus H-type vertical axis wind turbines (VAWTs). A large number of operational parameters, i.e., tip speed ratio (λ), Reynolds number (Re), turbulence inten-sity and reduced frequency (K) are investigated to provide a deeper insight into the impact of n on the dynamic loads on the blades, the turbine performance and the wake. High-fidelity unsteady Reynolds-averaged Navier-Stokes (URANS) simulations, extensively validated with experiments, are employed. The results show that (i) within the turbine optimal operational range, the turbine power coefficient (CP) is almost independent of n; (ii) when dynamic stall is present, CP values are dependent on n due to the impact of K; and (iii) decreasing n leads to an increase in the maximum lift coefficient, while the drag coefficient of the blade(s) reduces due to the higher K. The present findings support the optimal aerodynamic design of small- to large-scale VAWTs.