On the Intracycle Performance of a S-Shaped Vertical Axis Autorotation Current Turbine (VAACT) by Computational Fluid Dynamics

This research examines the intracycle performance of an original S-shaped Vertical Axis Autorotation Current Turbine (VAACT). This turbine has been developed at Laboratory of Waves and Currents (LOC-COPPE/UFRJ) and has been discussed by ITTC 2024. The investigation is performed by simulations using a two-dimensional Computational Fluid Dynamics (CFD) model. The V&V processes are as recommended practices from 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 LOC-COPPE/UFRJ. In the present case, the investigation focuses on VAACT, a highly efficient S-shaped original profile. In the CFD environment, the power take-off (PTO) system is modelled 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 o 135,000. The time series analysis indicates that both lift and drag 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. 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.