Aerodynamic analysis of Savonius and 3-bladed Darrieus-type vertical axis wind turbine utilizing NACA0012 and NACA0015 airfoils

Abstract

This study investigates the aerodynamic performance of vertical axis wind turbines (VAWTs) operating under low wind-speed conditions representative of inland and urban environments. A combined numerical-experimental approach was adopted, wherein the aerodynamic characteristics of a three-bladed Darrieus-type VAWT employing NACA0012 and NACA0015 airfoils were evaluated numerically, while complementary wind tunnel experiments were conducted on a geometrically accurate Savonius rotor to examine its low-speed performance. The numerical methodology for the Darrieus turbine was first validated against established benchmark studies and subsequently employed to perform transient Computational Fluid Dynamics (CFD) simulations using the sliding-mesh technique in ANSYS Fluent. Simulations covered Reynolds numbers ( Re ) ranging from 5.3 × 10 4 to 2.67 × 10 5 , with a near-wall grid resolution of 10 −5 m, convergence criterion of 10 −6 , and appropriate viscous models (laminar and k–ω SST) selected according to the flow regime. Experimental investigations on the Savonius turbine were carried out in a calibrated subsonic wind tunnel using 3D-printed Polylactic Acid (PLA) models over a Re range of 2.53 × 10 4 to 1.27 × 10 5 . The numerical study examined the influence of freestream velocity and tip speed ratio (2.0 ≤ TSR ≤ 3.0) on the lift coefficient, drag coefficient, and aerodynamic torque of the Darrieus turbine. At TSR = 2.5 and 6–10 m/s, the NACA0015 airfoil produced 21.9–84.3% higher cycle-averaged aerodynamic torque while reducing the Moment Fluctuation Index (MFI) by 14.8–22.6% compared to the NACA0012 airfoil. The experimental observations on the Savonius rotor further confirm its suitability for low-wind-speed operation and provide practical validation of VAWT performance under realistic conditions. The study highlights the influence of airfoil geometry on Darrieus turbine performance while demonstrating the effectiveness of Savonius rotors for low-speed applications, offering useful design insights for decentralized wind energy systems in regions with limited wind resources.