Design, optimization and analysis of a modified Savonius hydro-kinetic turbine (MSHT) with curved winglet and straight blade

•Novel hybrid curved winglet and straight blade for Savonius hydro-kinetic turbine.•Four turbine models designed and analysed through transient CFD simulations.•Taguchi optimized design parameters for the novel Savonius hydro-kinetic turbine.•Winglet best cut-out arc section and offset improve performance than traditional design.•Best model generates highest Cp and CT of 0.36 and 0.75 at optimal design conditions. The pico-scale power generation in remote locations is now very promising due to small-scale power requirements. The major challenge is harnessing the same from the run-off river streams or canals that have low free-stream flow-speed (less than 1 m/s). Savonius hydro-kinetic turbine can self-start in such flow streams, but it exhibits poor efficiency. This study proposes a novel airfoil-shaped curved winglet that can enhance the functionality of this turbine. The popular semi-circular blade is replaced with a hybrid blade profile consisting of a curved winglet at the front-edge, which is tore out from NACA 63415 airfoil, followed by a straight blade section up to the trailing edge, thereby resulting in a modified Savonius hydro-kinetic turbine. The curved winglet minimizes negative torque effect on the rotor, while the long straight edge offers a greater moment-arm and gap-flow. The research is performed in two stages. In the first stage, three different models of the turbine with various combinations of blade overlapping, side clearance, and winglet offset are designed. Transient Computational Fluid Dynamics (CFD) simulations are run to assess and compare the model performances under different low flow-speeds. Taguchi optimization is then performed to obtain a combination of best design and operating conditions for higher performance. In the second stage, two more design variables of the winglet, namely winglet arc angle and cut-out arc section are introduced on the previous best model and detail analysis is done to further improve the turbine performance. Finally, the two best models are compared to obtain important performance insights of the turbine. Results show that winglet parameters with best cut-out arc section and offset improve performance more than the performance with traditional overlapping or side clearance design considerations. The maximum Cp and CT of 0.36 and 0.75 are obtained for the best model at the best winglet arc angle (a1) of 30° for flow-speed 0.4 m/s, and TSR 0.7 with combinations of 20 % blade overlapping, 6.14 % side