Abstract
Plain flaps (PFs) significantly increase camber, enhancing lift and aerodynamic performance when deployed. In Darrieus Vertical Axis Wind Turbines (VAWTs), which perform efficiently in low-speed, turbulent wind conditions, structural modifications like PFs can improve efficiency. This study explores plain flaps with 10-20-degree deflections at different chord lengths to enhance the NACA 2412 aerofoil's performance. Using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and the Shear Stress Transport (SST) k-ω turbulence model, simulations were conducted across high (Re ≈ 2.71 × 10(5)), medium (Re ≈ 1.35 × 10(5)), and low (Re ≈ 5.4 × 10(4)) Reynolds numbers (Re). The 0.7-10 and 0.8-10 configurations significantly improved torque and Cp. At a Tip Speed Ratio (TSR) of 2.5, the 0.8-10 configuration increased the Cp by 19.51% over the flapless NACA 2412 without PF. The 0.7-10 configuration achieved the highest Cp across all TSRs, while a three-blade setup improved Cp by 43% compared to four- and five-blade configurations. The modified blades demonstrated consistent torque gains across all Re, proving the effectiveness of blade shape modifications in enhancing VAWT efficiency, particularly under fluctuating wind conditions, indicating the potential of PF-modified blades in improving small-scale wind turbine performance in varied urban environments.