Impact of Scaling on the Performance and Wake Characteristics of Paired Counter-Rotating Vertical Axis Wind Turbine

Abstract This study investigates the aerodynamic performance and wake dynamics of counter-rotating vertical-axis wind turbines (VAWTs) through two-dimensional computational fluid dynamics (CFD) simulations. The analysis focuses on the effects of geometric scaling, wherein the turbine diameter is increased tenfold, leading to a rise in the chord-based Reynolds number from 2.1 × 10 5 to 2.65 × 10 6 . This transition surpasses the critical threshold of 1.5 × 10 6 , which is associated with marked improvements in aerodynamic efficiency for VAWTs. The results show that, for the baseline configuration, outward-rotating turbines spaced at 1.15D yield the lowest power coefficient. However, at larger scales, the performance at this same spacing improves significantly, indicating that higher Reynolds numbers may mitigate adverse wake interactions and enable more compact turbine arrays. A consistent increase of approximately 21% in power coefficient is observed for spacings ≥ 1.25D between the baseline and scaled models. Furthermore, the study indicates that outward rotation at an azimuthal offset of β = 60° outperforms inward rotation, maintaining superior torque and aerodynamic efficiency across scales. Wake structure analysis reveals that scaled turbines produce more centralized vorticity and reduced wake velocity deficits, which suggests enhanced kinetic energy extraction and a more streamlined wake profile. Overall, the results demonstrate the potential of turbine scaling to improve VAWT performance and inform the design of more efficient wind farm configurations.