Design optimization of an innovative deflector with bleed jets to enhance the performance of dual Savonius turbines using CFD-Taguchi method

Savonius rotor is an attractive type of Vertical-Axis Wind Turbine (VAWT) for small-scale and urban applications, due to its simplicity in design and self-starting capability. However, because of having negative torques on their returning blades, these turbines have poor power generation effectiveness. In the current research, an innovative deflector is proposed which has a cylindrical shape with bleed jets to augment the performance of dual Savonius rotors. The bleed jets are released from the narrow slots directed from the front stagnation point to the locations close to the top and bottom separation points to produce perturbations in the flow. The bleed jets interact with the boundary layer and modify the wake shear layer over the deflector. Also, a Design of Experiment (DoE) methodology based on the Taguchi method and Analysis of Variance (ANOVA) is employed to optimize the design variables including five factors with three levels for a deflector system that enhances the output power of dual rotors. Analysis of the results showed that W (distance between adjacent rotors) is the main influencing factor on the performance of the dual rotors, and its contribution factor is 61%. The maximum average power coefficient (CP) of dual rotors with optimized deflector is found to be 0.636, which is 166% higher than the peak average CP of a single rotor without deflector at Tip Speed Ratio (TSR) = 0.8. Furthermore, using the deflector with optimal design enhanced the average CP of the dual rotors by 14% and 19% compared to dual rotors without deflector at TSR = 0.8 and TSR = 1.2, respectively.