Three-dimensional numerical analysis of a vertical axis autorotation current turbine (VAACT): Effects of lateral blockage and free surface

In this study, we conduct an in-depth three-dimensional (3D) numerical analysis of an innovative vertical axis
autorotation current turbine (VAACT), focusing on examining the effects of lateral blockage and free surface
on its performance. This analysis employs detached eddy simulation (DES) integrated with the sliding mesh
and the volume of fluid algorithm. To begin with, the time series data of angular velocities acquired during the
power output phase indicates that, within the range of 0.05 to 0.213, an increased blockage ratio positively
influences the turbine’s rotational stability and improve its efficiency. Further, the extrapolation from the fitted
curve of the mean power coefficient (𝐶𝑃 ) as a function of lateral blockage ratio suggests that, in the absence
of lateral blockage, the 𝐶𝑃 value would approximate 0.145. Additionally, it is observed that the free surface
generally diminishes the turbine’s rotational speed and power. This effect is particularly pronounced when the
free surface fluctuation is large relative to the turbine’s submerged height. Notably, two parallel rows of 3D
vortices on the free surface periodically detach in the wake, and the vortices downstream of the retreating edge
appear stronger. This study also presents and analyses detailed flow field characteristics, including 3D vortical
structures, free surface fluctuations, and vorticity contours. Overall, this research enhances the comprehension
of this innovative vertical-axis turbine, offering valuable knowledge for its potential practical deployment.