Parametric study on self-starting capability and aerodynamic performance of a hybrid J-shaped Darrieus vertical axis wind turbine

Darrieus vertical axis wind turbines (VAWTs) are a class of lift-based wind turbines known for their high efficiency across a broad spectrum of tip speed ratios (TSRs). However, they often suffer from poor self-starting capabilities due to low net torque in the windward section, particularly at low TSRs. To address this limitation, hybrid J-shaped blade configurations—featuring a primary row of clean blades and a secondary row of J-shaped blades—have recently gained attention for their potential to enhance startup performance. To fully harness the advantages of this novel configuration, this study aims to conduct a comprehensive parametric investigation to assess and optimize its aerodynamic performance and self-starting capability. Specifically, three key design parameters are examined: (1) the diameter ratio between the inner and outer rotors, (2) the phase angle between the main and secondary blades, and (3) the orientation of the openings in the J-shaped blades. These findings reveal that the optimal configuration features an outer-facing J-blade opening, a diameter ratio of 1.3, and a phase angle of 0°. This setup extends the effective TSR range down to 0.5, significantly improving self-starting behavior. Additionally, it increases the power coefficient (C_p) by up to 140% in the medium-TSR range and enhances the moment coefficient (C_m) by up to 80% at an azimuth angle of 75°, particularly when the blades are in the upwind position. These results demonstrate the potential of the hybrid J-shaped design to address one of the key performance bottlenecks of conventional Darrieus VAWTs.