Complexity-Aware Design Analysis of the Efficiency in Darrieus Vertical Axis Wind Turbines

This study proposes a numerical investigation for assessing the primary design parameters influencing the efficiency of a Darrieus type vertical axis wind turbine. The methodology consists in the numerical solution of the continuity and momentum equations utilizing the Unsteady Reynolds Averaged Navier-Stokes (URANS) approach. The turbulence closure model is the SST k-ω, and the Finite Volume Method is applied to solve the three-dimensional geometries. The findings confirm that variations in solidity and aspect ratio of twisted blade turbines, in comparison to straight blade configurations, exert a similar influence on the torque coefficient, surpassing the impact of blade torsion angle variations. Results corroborated previous findings of literature about the fluctuations in the torque coefficient (Cm) being smoothed in 55% when helical blades are used in comparison with straight configuration. However, the increase in blade torsion angle corresponded to a decrease in the torque coefficient, with maximum difference of 37% when solidity (σ) is σ = 0.75 and the ratio between height and radius of the turbine is H/R = 1.5. Results also demonstrated that the increase in the solidity from σ = 0.4 to 0.8 reduced the effect of the ratio H/R on the Cm. The increase of σ allowed a gain in Cm of nearly 60%. For constant σ and tip speed ratio (λ), the increase of H/R from 2.5 to 7.5 led to an increase of 79% in Cm. In general, results supplied a guideline on the influence of λ, twisted angle, σ, and H/R on the performance of helical Darrieus turbines.