On the Intracycle Performance of an S-Shaped Vertical-Axis Autorotation Current Turbine by Computational Fluid Dynamics

Abstract

Abstract. This research article examines the intracycle performance of the S-shaped vertical-axis autorotation current turbine (VAACT). The investigation is performed by simulations using a two-dimensional computational fluid dynamics (CFD) model. The verification and validation (V&V) processes are as recommended practices from the International Towing Tank Conference (ITTC) 2023. The verification process includes checking the domain, grid, and time-step, leading to a convergent result with sufficient grid elements. The validation process uses comparison with the model results performed at the current channel of the Laboratory of Waves and Currents (LOC-COPPE/UFRJ). The test facility presents 22 m in length, 1.4 m in width, and a maximum flow velocity of about 0.50 m/s at 0.5 m water depth. In the present case, the investigation focuses on VAACT, a highly efficient S-shaped profile. In the CFD environment, the power take-off (PTO) system is modeled by adding an external torque due to the PTO system and the damping coefficient (Kt) into a user-defined function (UDF). The validation is performed at Reynolds numbers ranging from 70,000 to 135,000. The time series analysis indicates that lift (crossline) and drag (inline) forces are crucial to the turbine’s performance. The intracycle analysis shows that although the instantaneous efficiency is in phase with the drag force, the lift drives the device when the drag achieves smaller magnitudes close to 0- to 30-deg encounter angle. Additionally, the torque coefficient is in phase with the lift force, which implies that it can govern hydrodynamic performance. The analysis also reveals that the returning blade adds a resisting torque on the turbine, which impacts its performance, as represented by high-pressure points on this blade. The torque coefficient drops by 38% from 45 deg to 90 deg because of this resisting effect.