Hydrodynamic Investigation of a Hybrid-Bladed Savonius Hydrokinetic Turbine - Computational Fluid Dynamics and Taguchi Optimization Approaches

This study entails an optimal airfoil-based curve section attached to a straight blade segment, forming a hybrid-bladed Savonius hydrokinetic (HSHT) turbine design. The aim is to investigate its detailed hydrodynamic performance under various design and flow conditions, common in low discharge channels. Three turbine types are conceptualized with different arc radii and aspect ratios. Initially, transient computational fluid dynamics (CFD) simulations are performed to investigate torque variation and compare their flow physics, which is followed by Taguchi optimization. Further, detailed CFD simulations have been carried out. The Taguchi optimized turbine design showcases five blade-fluid flow control-based interactions- i) advancing blade's arc curvature flow control (both pressure and suction sides), ii) overlapping and side gap flow control, iii) curve edge gap flow control, iv) Coanda-vector like flow control, and v) vortical flow control, which make the optimal turbine design a better choice for pico-scale power generation. When the optimal curve profile (15 mm arc radius) and optimal aspect ratio (0.51) are used with water flow stream-speed 0.5 m/s, it exhibits a maximum C_p of 0.272 and C_t of 0.68, respectively, for tip-speed ratio 0.7. Blade overlapping 20% and thickness 2 mm further enhance C_p and C_t by 2.20% and 3.23%, respectively.