CFD-based comparative evaluation of Savonius rotors with 2,3,and 4 blades at low wind velocity under varying aspect ratios

Abstract

The growing demand for clean and reliable energy highlights the importance of improving wind turbine technologies, particularly for decentralized power generation in low-wind-speed environments. Savonius rotors, a type of vertical-axis wind turbine, offer simple design, and cost advantages but remain limited in aerodynamic efficiency. This study examines the impact of blade aspect ratio, blade number, and end-plate (EP) integration on rotor performance. A total of 180 high-fidelity three-dimensional computational fluid dynamics simulations were performed using the realizable k–ε turbulence model and a sliding mesh approach to resolve unsteady flow fields around 2, 3 and 4-bladed rotors across six aspect ratios (0.5, 1, 2, 3,4, and 5), both with and without EPs. The results show that two-bladed rotors consistently outperform multibladed designs, achieving a maximum power coefficient of 0.234 at a tip speed ratio of 0.785, compared with 0.199 and 0.169 for 3 and 4-bladed designs, respeively. The addition of EPs enhanced efficiency by mitigating tip losses, with the highest power coefficient of 0.246 obtained for a 2-bladed EP rotor with an aspect ratio of 5. An increase in aspect ratio from 0.5 to 5 was found to improve energy capture by 15% to 30% across all configurations, with higher ratios providing the greatest gains. The study concludes that a two-bladed, high aspect ratio rotor with EPs is the most effective configuration for maximizing efficiency at low wind speeds. The novelty of this work lies in its comprehensive, systematic evaluation of geometric and design parameters through large-scale computational fluid dynamics analysis, providing quantitative insights into the combined effes of blade number, aspect ratio, and EP configuration on Savonius rotor performance, an area not simultaneously addressed in previous studies.