Aerodynamic Performance of a Two-Stage Savonius Wind Turbine

Abstract

The Savonius wind turbine (SWT) is widely recognized for its self-starting capability, and suitability for low wind speed regimes. However, its performance is still limited with low power coefficient. This study therefore aims to improve aerodynamic performance by introducing geometric variations of the blade design for a two-stage SWT. This study applies a novel approach to geometric variation by introducing targeted geometric variation in the blade design. To modify the shapes of the blade, the diameter on right hand side (RHS) and left hand side (LHS) along X-axis was varied on a 20:-20 range. For the other set of geometry, the radius on right hand side (RHS) and left hand side (LHS) along Y-axis was varied on a 10:-10 range. Computational Fluid Dynamics (CFD) simulations were conducted using ANSYS FLUENT to evaluate the aerodynamic performance based on phase shift angle, with the best performing phase shift selected for further study of geometric variations based on cross-sectional length and shape. Key findings reveal that the two-stage Savonius turbines with a phase shift angle (PSA) of 00 had a better power coefficient (Cp) of 0.19 compared to turbines with PSA 450 and 900. This was attributed to blade alignment with a synchronous exposure to the wind. Geometric variations on the X-axis dimension significantly improved aerodynamic performance compared to other variations due to a great blade aspect ratio. The turbine blade with cross-sectional X-dimensions of 210 mm on RHS and 130 mm on the LHS exhibited the highest power coefficients of 0.35, 0.33 and 0.30 for wind speeds of 7, 5 and 3m/s respectively. The geometric variations on the Y-axis however, did not show any significant improvement, with the highest Cp obtained being 0.16, 0.17 and 0.18 compared to 0.17, 0.19 and 0.20 of the semi-circular turbine across the three wind speeds tested of 3, 5 and 7m/s respectively. The study concluded that geometric variations significantly enhance the performance of a two-stage SWT