CFD Simulation and Experimental Validation of a Vertical Axis Turbine: Toward Variable Pitch Cross-Flow Marine Turbine for Maximizing Hydropower Extraction—The SHIVA Project

The paper describes the numerical simulation of a cross-flow axis water turbine, widely known as Darrieus turbine or VAWT. The numerical solver is the RANSE solver CFX. The method of resolution aims at calculating the instantaneous forces on the blades of such a turbine, and the energy produced. Due to the specific blade kinematics that can result of pitch variable systems and the complex flow particularly in the centre part of the turbine, a meshing strategy based on the mixing of both sliding or/and deforming mesh were used. Due to the moderate Reynolds number involved in such systems, various fluid models were used including laminar flow, fully turbulent model as k–ω SST model and a laminar-turbulent transition model. A convergence study was carried out for time step, which yielded to courant number lower than 5 and angular step below 1° with about 600.000 cells with y+ = 1. Fixed pitch devices were simulated for comparison with experiments data available in the literature to validate the numerical model. The normal and tangential forces were compared for various flow conditions. The number of blades ranged from 1 to 3, the Tip Speed Ratio ranged from 1.5 to 7.5, the Reynolds number was about 4×10⁴. It was observed that the agreement between the experiments and the numerical results is very good with the turbulent model in all cases excepted for one low TSR case for which the blade section incidence is maximum. Next step will consist in running simulations with variable pitch.