Performance evaluation of a novel vertical axis wind turbine using twisted blades in multi-stage Savonius rotors

To enhance the performance of vertical axis wind turbines, a new configuration using twisted blades in multi-stage Savonius rotors is developed. Accordingly, single-, two-, three-, and four-stage Savonius rotors with twisted blades are investigated and compared with a single-stage rotor at corresponding aspect ratios ranging from 1 to 4. To determine performance parameters such as torque, power, and thrust coefficients, a comprehensive three-dimensional unsteady incompressible turbulent flow model using Reynolds-Averaged Navier-Stokes equations along with k-ω shear-stress transport turbulence model is developed. The developed numerical model is validated using the available numerical and experimental results. Furthermore, a novel assessment technique relying on flow field characteristics such as pressure distribution in conjunction with streamlines around the proposed multi-stage Savonius rotor with twisted blades is carried out. The contribution of each stage on the performance of the whole rotor is also computed and presented. The findings of this study show that the new design of the multi-stage rotor with twisted blades significantly enhances the output power. The maximum power coefficient is found to be 0.253 for a two-stage rotor and reaches 0.261 for a four-stage rotor and about 0.223 for a single-stage rotor. In addition, the multi-stage rotor with twisted blades significantly mitigates the oscillations of both torque and thrust coefficients throughout the whole cycle. This lowers the mechanical vibrations and noise emission during operation conditions. The static torque coefficient is found to have positive values with smooth fluctuations at all rotational angles. This results in enhancing the self-starting capability of the multi-stage rotor with twisted blades and making it suitable in areas where the wind is intermittent and very low. The large benefits offered by the proposed multi-stage Savonius rotor with twisted blades model is comparable to alternate designs of vertical axis wind turbines currently in the market.