Turbulence modelling in Alderney Race using LANS-α model
Résumé
Alderney race in France represents one of the most promising tidal site in Europe. In this region where current reaching 5m/s, an accurate modelling of turbulence is necessary to compute the tidal energy estimate. On the basis of the works of Hecht and al. (2008) and Petersen and al.(2008), we have augmented the coastal circulation code MARS (Lazure et Dumas, 2008) with the Lagrangian Averaged Navier–Stokes–alpha (LANS-α), a Large Eddy Simulation turbulence model. In comparison with former dissipative turbulence models implemented in MARS (e.g. Two equations eddy viscosity turbulence models), LANS-α is more energetic and produce more eddy structures near the grid scale. Firstly, validation of our implementation is made within an idealized test case similar to the one used by Hecht and al. (2008). We have shown the ability of LANS-αmodel to reproduce both horizontal and vertical patterns obtained at higher-resolution simulations with MARS. Finally, the LANS-αmodel is applied in the Alderney race with a fine realistic bathymetry and meteo-oceanic forcing. It appears that LANS-α produces higher kinetic and eddy kinetic energy than the ones computed by MARS with eddy viscosity models, allowing to capture small turbulent structures induced by the seabed variations.