Three-dimensional CFD-ALM-VOF modeling of hydrokinetic turbines in realistic open-channel conditions

The potential of Darrieus-type Vertical Axis Turbines (VATs) in hydrokinetic applications, especially when deployed into arrays or clusters, has gained recognition in the field of distributed energy production. Due to the complex unsteady hydrodynamics of these turbines and the different flow scales involved, numerical studies to date have often focused on one system component only (turbine or channel). This study presents an integrate, accurate, but computationally feasible simulation approach applied to an array of VATs in a free-surface channel. The turbines are modelled using the Actuator Line Method (ALM), while the water free surface is modelled using the Volume of Fluid (VOF) approach, both included within the RANS solver of Ansys Fluent. A sensitivity analysis is conducted on the most appropriate model settings, followed by a validation campaign with field data that showed good agreement between experiments and simulations. Results point out the significance of the two-way interactions between the turbines and the channel, emphasizing the impact of the variation in water level and inflow velocity on the efficiency assessment of hydrokinetic turbines. The study also exploits the current 3D model to get a better understanding of the interaction effects between closely spaced turbines, and their influence on the power augmentation mechanisms in an array of turbines, which were so far mainly analyzed only with 2D approaches. Finally, the hydraulic impact on the channel is discussed, highlighting the effects and limitations of clustering hydrokinetic arrays in a confined channel.