Numerical investigation on the effect of blade count on the performance of a small-scale Savonius wind turbine

Abstract

The growing demand for clean energy has increased interest in small-scale wind turbines, particularly vertical axis wind turbines (VAWTs), which perform well in turbulent wind conditions and low wind speeds. This study numerically analyzes Savonius rotors with two, three, and four blades to evaluate their aerodynamic performance in uniform inflow. Simulations were performed with a steady-state multiple reference frame (MRF) model at an inflow velocity of 10 m/s. Key parameters used included the torque coefficient ( 𝐶𝑇 ), power coefficient ( 𝐶𝑝 ), and tip speed ratio ( 𝜆 ). The results show a clear trade-off between configurations. The four-blade rotor produces the highest torque (0.1297 N·m at 950 rpm) and strong self-starting capability, although its peak efficiency ( 𝐶𝑝 ≈0.60) is likely too high due to model simplification. The two-bladed rotor achieves higher efficiency ( 𝐶𝑝 ≈0.24) at 𝜆 ≈0.52 but exhibits significant torque fluctuations. Conversely, the three-bladed rotor produces the lowest efficiency ( 𝐶𝑝 ≈0.086) but offers smoother torque, beneficial for stable small-scale power generation. Flow analysis confirms this pattern: two blades cause a wide, asymmetrical wake; three blades reduce wake asymmetry with better stability; and four blades produce a compact wake but with higher drag. Overall, the optimal number of blades depends on design priorities—efficiency, torque, or operational smoothness.