Flow control optimization for helical Savonius hydrokinetic turbines using a progressive diverter

Abstract

The rising demand for environmentally friendly energy has led to a surge in interest in hydrokinetic turbine technology, particularly for applications in low-flow water environments such as rivers and tidal streams. Among various turbine designs, the Savonius turbine stands out for its simplicity, durability, and ability to self-start under low-speed conditions. This study presents an investigation of a helical Savonius hydrokinetic turbine equipped with a novel design of orientable diverter systems aimed at improving flow behavior and turbine performance. The proposed design consists of three guiding walls that are symmetrically orientable with respect to the rotor. The optimal orientation of these walls was examined to assess their impact on the flow field and torque coefficient. To perform the Computational Fluid Dynamics simulations, Ansys Fluent was used to analyze the velocity, pressure, and turbulent kinetic energy distribution around the rotor, as well as the resulting torque output. The results demonstrate that diverters significantly influence the incoming flow structure, which in turn affects the turbine's performance. All proposed diverter configurations produced higher power coefficient (C_p) values compared to case 0 (without diverter). At tip-speed ratio 0.7, the relative increases in C_p compared to case 0 are 18.5%, 31.9%, and 35% for cases 1, 2, and 3, respectively, with case 3 achieving the highest improvement. These findings highlight the importance of optimizing the diverter angle to maximize the effectiveness of Savonius-based hydrokinetic systems.