Performance enhancement of Darrieus wind turbines using Plain Flap and Gurney Flap configurations: A CFD analysis

Darrieus vertical axis wind turbines (VAWTs) have limited self-starting torque, especially in urban areas with low and changing wind speeds. This study modifies NACA 0015 aerofoils with Plain Flaps (PF) and Gurney Flaps (GF) to improve aerodynamic performance for urban solar wind tree systems. The k-omega Shear Stress Transport (SST) URANS model was used to simulate different configurations at varied Tip Speed Ratios (TSRs). The 0.6c, 10 degrees PF configuration achieved the highest power coefficient (Cp) of 0.46 at TSR 2.5, a 9.8 % increase over the baseline NACA 0015. Additionally, PFs reduced negative torque and achieved the highest peak average torque across configurations, significantly boosting self-starting capability and torque consistency under low Reynolds number (Re) conditions. GF configurations, especially the 0.25c, 120 degrees GF, provided stable torque generation, enhancing performance under variable wind conditions. These findings indicate that optimizing VAWTs for urban use requires balancing peak efficiency with torque stability. Future work should focus on adaptive flap designs capable of real-time optimization, alongside experimental validation.