Investigation of the effect of blade angle of Archimedes spiral hydrokinetic turbine based on hydrodynamic performance and entropy production theory

The Archimedes Spiral Hydrokinetic Turbine (ASHT) represents a novel design specifically engineered to operate in low-speed ocean currents. However, the characteristics of energy losses associated with these turbines have not yet been fully understood. This paper examines nine ASHTs with varying blade angle configurations. The analysis of the hydrodynamic performance and energy loss characteristics of these turbines, under both axial and yawed flow conditions, is conducted using computational fluid dynamics in conjunction with entropy production theory. The results indicate that ASHTs with larger blade angles can operate across a broader range of tip speed ratios, achieving optimal power performance at higher tip speed ratios and generating greater thrust. In contrast, variable blade angle configurations demonstrate higher peak power but exhibit lower thrust and a narrower operating range of yaw angles compared to their fixed blade angle counterparts. The wake region behind the ASHT with a larger blade angle is characterized by a more extensive low-velocity area and a prominent hub recirculation zone. The energy loss occurring in the wake region is primarily attributed to the vortices generated at the tip and hub, with hub vortices being the main contributors to increased entropy production rates for configurations with larger blade angles. Under yawed flow conditions, an increase in yaw angle results in significant reductions in power and thrust, altered wake structures, and an increase in total entropy production. These findings provide crucial insights for the design and optimization of ASHTs, ultimately contributing to the development of more efficient and cost-effective ocean current power generation systems.