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

• Published in: Energy conversion and management 2021-05, Vol.235, p.114013, Article 114013
• Main Authors: Saad, Ahmed S., Elwardany, Ahmed, El-Sharkawy, Ibrahim I., Ookawara, Shinichi, Ahmed, Mahmoud
• Format: Article
• Language: English
• Subjects: Aerodynamics; Aspect ratio; Blades; Coefficients; Fluid flow; Incompressible flow; Mathematical models; Maximum power; Multi-staging; Numerical models; Oscillations; Performance evaluation; Performance improvement; Pressure distribution; Reynolds averaged Navier-Stokes method; Rotors; Self-starting capability; Three dimensional flow; Thrust; Torque; Turbines; Turbulence models; Turbulent flow; Twisted blades; Vertical axis wind turbines; Vibrations; Wind power; Wind turbines
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2021.114013

•A new configuration using twisted blades in multi-stage Savonius rotors is developed.•The proposed multi-stage rotors with twisted blades significantly enhance the output power.•The multi-stage design mitigates the torque oscillations and enhances self-starting ability.•The new design is very competitive with other designs of vertical axis wind turbines. 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.