Influence of profile geometry on the self-starting capability of an H-Darrieus turbine

Abstract

To spread the use of Wind H Darrieus turbines to electricity generation in urban or rural environments is necessary to improve some of its main drawbacks such as: aerodynamic efficiency, self-starting capability and torque fluctuations. The aims of this study are to enhance the aerodynamic efficiency and self-starting capability of an H-Darrieus turbine through wind tunnel tests combined using a 3D numerical study using Computational Fluid Dynamics (CFD). The NREL S815 profile and four modified versions were evaluated, including one with a 19.2% increase in thickness and three chord-to-diameter ratios:=0.15, 0.20, and 0.225. These configurations were tested at wind speeds of 6 and 8 m/s. Static torque was measured experimentally, alongside numerical alculations of flow and pressure distribution. A significant correlation between chord length and turbine performance was observed. The =0.20 profile exhibited increases of up to 50.27% and 58.88% in static torque at 6 and 8 m/s, respectively. The static torque coefficient increased from 0.0063 in the original profile to 0.0447 in the C/D=0.20 profile, directly contributing to the improvement of self-starting capability. Although the =0.20 geometry showed improvements, the C/D=0.225 rofile did not show additional performance gains, indicating that further increases in chord length do not improve turbine performance. The profile modified with a 19.2% increase in thickness ranked just below the =0.2 profile, exhibiting torque ncreases of 41% and 25.22% at 6 and 8 m/s, respectively. These findings confirm that chord-to-diameter ratio adjustments lay a critical role in boosting torque generation in vertical-axis wind turbines.