Modelling turbulence with an Actuator Disk representing a tidal turbine

RANS turbulence models in association with the Actuator Disk theory is among the most popular concepts to predict the wake of tidal turbines. This methodology has the advantage of giving accurate results at affordable computing costs. In this paper, several turbulence models usually used to simulate the wake behind a turbine represented by a porous disk are compared. The tested models are the Standard and the Realizable k-ε models, the SST k-ω model and the Reynolds Stress Model (RSM). The results of the simulations are validated against experimental data measured behind a porous disk placed in a laboratory water flume. The experimental data consist of a set of turbulence intensity and velocity profiles. Without modifying the turbulence models, both velocities and turbulence intensities are well simulated by all the models in the far wake. However, in the near wake, the results strongly differ from one model to another. In the vicinity of the disk, the Standard k-ε model provides the most accurate results. The other models tend to underestimate the turbulence production as the fluid passes through the disk. To compensate this, another set of simulations are performed adding TKE (Turbulent Kinetic Energy) within the porous disk. The optimal amount of additional TKE differs from one model to another. Except for the Standard k-ε model, the correlation between the model and the experimental results is significantly improved when enhancing the TKE in the area occupied by the disk.