Vertical-axis wind turbines (VAWTs) promise advantages over conventional horizontal-axis designs, including omnidirectional wind capture and simpler installation. However, their aerodynamic behavior under varying atmospheric conditions remains incompletely understood. Researchers performed a parametric computational study on a three-bladed H-type Darrieus rotor with NACA 0021 airfoils to evaluate how inlet turbulence intensity influences power generation across different operating regimes.
The analysis employed two-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) simulations with the k-ε turbulence model, testing six turbulence intensity levels from 1% to 25% combined with five tip speed ratios from 1.5 to 3.5. Freestream velocity was maintained at 9 m/s across 30 total simulation cases. Validation against experimental reference data showed excellent agreement, with peak power coefficient deviation of just 3.7%.
Key findings reveal that the optimal operating point remains stable at a tip speed ratio of 2.5 regardless of atmospheric turbulence conditions. At this optimal condition, power coefficient decreased modestly by 6% as turbulence intensity escalated from 5% to 25%. However, at lower tip speed ratios like 1.5, the same turbulence increase caused substantially larger performance degradation of 17%. Interestingly, at intermediate conditions (tip speed ratio of 2.0), a slight nonmonotonic response occurred, where higher turbulence marginally improved performance by 1.5% compared to low-turbulence conditions.
Flow visualization through vorticity contours indicated increasingly diffuse wake structures at elevated turbulence intensities. These observations suggest that turbulent conditions affect blade boundary layer dynamics, though the two-dimensional analysis framework limitations precluded definitive characterization of flow separation and dynamic stall phenomena.
The research underscores the importance of operating VAWTs near their optimal tip speed ratio to minimize turbulence sensitivity. However, the authors emphasize that three-dimensional analysis of finite-span rotors is essential to validate whether these two-dimensional trends translate to practical full-scale turbine designs.
