Parametric analysis of blade pitch angle modifications for enhanced H-Darrieus turbine efficiency

At low wind speeds, H-Darrieus wind turbines suffer from pronounced cyclic variations in the blade angle of attack (AoA), triggering premature dynamic stall and impeding self-starting capability. These aerodynamic instabilities, combined with high cyclic loading, compromise both energy extraction efficiency and structural durability, presenting a critical barrier to the adoption of H-Darrieus technology. While fixed or dynamic pitch control strategies can mitigate excessive AoA fluctuations, their comparative effectiveness remains poorly characterized. This study systematically evaluates four pitch control strategies including zero-pitch, fixed-pitch, sinusoidal pitch, and helical blade configurations to assess their impact on the aerodynamic performance of a small-scale, three-bladed H-Darrieus rotor operating at 7 m/s wind speed. A high-fidelity 3D unsteady aerodynamic model, combining a lifting line approach with a free vortex wake method, is employed to resolve transient flow phenomena and blade-wake interactions. Results demonstrate that a sinusoidal pitch modulation strategy amplifies torque generation by almost six times compared to the zero-pitch baseline, while fixed-pitch configurations show negligible efficiency gains. Notably, negative fixed-pitch angles outperform their positive counterparts in torque production. Furthermore, blade helicity is shown to reduce aerodynamic load fluctuations by 22%, offering dual benefits in efficiency enhancement and structural load mitigation. These findings provide actionable insights for optimizing pitch control strategies in small-scale vertical-axis wind turbines, particularly in urban and low-wind environments.