A comprehensive investigation on Darrieus vertical axis wind turbine performance and self-starting capability improvement by implementing a novel semi-directional airfoil guide vane and rotor solidity

Darrieus vertical axis wind turbine is classified as a lift-based power generation turbomachine. However, it is burdened with the limitations of mid-range efficiency and requiring initial torque for startup. The quest to improve the turbine's performance has focused on enhancing its aerodynamic performance and self-starting ability. One of the most effective approaches is to flow control and injection toward the rotor blades. This computational fluid dynamics research study utilizes a novel geometry known as the “Semi-Directional Airfoil Guide Vane” (SDAGV) to inject airflow smoothly and effectively toward the rotor blades at the upstream section. The investigation found that using a two-passage SDAGV increased rotor efficiency by up to 55% at a tip speed ratio (TSR) of 2.5. The pressure distribution analysis showed that azimuth angles between 90° and 135° significantly impacted the rotor's self-starting ability. Additionally, studying the turbine solidity revealed that a five-bladed rotor with SDAGV had a higher self-starting capability and efficiency than a two-bladed rotor with SDAGV. This was because its power coefficient (Cp) was approximately 160% greater at TSR = 1.4. Due to blade-to-blade interaction, high-solidity turbines from TSR = 2 onwards face performance challenges, which means their efficiency drops in the low-TSR range.