A computational fluid dynamics investigation of a cambered auxiliary blade-assisted rotor for enhancing the self-starting capability of Darrieus vertical axis wind turbines

The limited self-starting capability of lift-based Darrieus vertical axis wind turbines (VAWTs) represents a significant challenge to their broader adoption, particularly within the low-tip speed ratio (TSR) range. To address this issue, a two-dimensional computational fluid dynamics model with a midplane assumption, which may slightly overestimate aerodynamic response due to unresolved tip vortices, was developed to explore an auxiliary blade-assisted Darrieus VAWT featuring various cambered blade configurations. A total of nine rotor arrangements were analyzed by manipulating the orientation of both the primary and auxiliary blades, utilizing symmetrical, positively cambered, and negatively cambered airfoils. The predicted numerical results reveal that the auxiliary blade-assisted rotor markedly improves aerodynamic performance in terms of self-starting capability across most configurations. At TSR = 2, configurations utilizing symmetrical and negatively cambered blade sets predict an increase in power coefficient (Cp) of 40.28% and 34.21%, respectively, compared to the control case. The configuration that yielded the largest predicted enhancement in equivalent torque was one where both blades were negatively cambered, producing a 25% increase in moment coefficient (Cm) and a 34% predicted improvement in lift coefficient (Cl). Conversely, arrangements with positively cambered auxiliary blades reduced Cm by 11.07% at the initial azimuth angles. Flow-field analysis showed that the optimal configurations produced advantageous high-pressure regions and maintained attached flow up to an azimuth angle of 135°, contributing to higher torque production and improved self-starting characteristics. These results underscore the potential of auxiliary blade-assisted rotors as a viable means of enhancing the startup performance of Darrieus VAWTs.