CFD analysis of an innovative combined lift and drag (CLD) based modified Savonius water turbine

Highlights: • An innovative CLD Savonius turbine design has been proposed. • CFD simulations for the performance analysis of the turbine using different design and boundary conditions. • The combination effect of different design parameters has been investigated using orthogonal experiment. • A series of performance curve of the turbine has been obtained at different Reynolds number. • The coefficient of power of the turbine is found to be higher than the base model of Savonius turbine. - Abstract: Savonius water turbine is a popular turbine that can be used for energy extraction from free stream flows in rivers or manmade channels and also from tidal and ocean currents. The present study aims at developing a new combined lift-drag (CLD) based blade design for a conventional two-bladed Savonius water turbine. The semicircular blade is replaced with a straight blade section starting from the turbine axis and ending with an airfoil blade section at the leading edge. The blade lengths are adjusted within the overall diameter of an established conventional Savonius water turbine, taken from available literature. This innovative design is considered as the base model. The base model is then gradually modified and optimized using ANSYS Fluent 14 CFD software by considering design parameters – gap width ratio and overlap ratio. The evolved optimal design is then further studied for two more turbine diameters, one of which is taken from another prominent literature. All the performance analyses are carried out through flow physics study of the turbines. It has been found that the maximum coefficient of power $\left(C_p\right)$ obtained for the CLD Savonius turbine is 0.284 obtained at a tip speed ratio 0.6 for an overall turbine diameter 260 mm, gap width ratio 8.45%, and overlap ratio 46.9%. The contributions of the individual blade sections on the CLD turbine performance have also been appreciated. Finally, the CLD design is compared with an established Savonius turbine design to highlight the significant importance of the present design.