Towards a realistic numerical modelling of the wave-current-turbulence interactions in Alderney Race
Résumé
Alderney race is the most energetic tidal site in western Europe, with currents reaching 12 knots. High winds sweeping across the Channel make wave-current interactions could be crucial to the tidal energy estimate. Following the works of Lewis et al. (2014) and Guillou et al. (2016) for several UK tidal sites and Fromveur (France), our work focuses on impacts of wave-current interactions on tidal energy, which is proportional to the velocity cubed. The 3D fully-coupled wave-current model, MARS-WAVEWATCH III, based on the vortex force method (Ardhuin et al., 2008, Bennis et al., 2011), is tested against ADCP data for three locations with different energetic conditions (wave height up to 2.5m, wave length up to 200m, wave period up to 17s). On the whole and for our meteo-oceanic conditions, the including of wave-current interactions in numerical simulations reduces by 10 % the error on tidal energy estimate. Best fits are obtained at flood tide, with a tidal assymetry which is in agreement with observations. The bottom stress parameterization of Soulsby (1995) has been adjusted to the case, with a modification of the current stress. Wave refraction by currents causes wave breaking which mixes the surface current. Simulations for wind-sea are more successful than the ones with swell. A rephasing of the tidal current by waves is observed. Vertical shapes of current are especially modified near the surface by waves with acceleration or deceleration, as expected, and are closed to the observations (see Figure below), which validates our modeling platform. However, some improvements are needed to the turbulence modelling. The implementing of a new turbulence model (based on the Large Eddy Simulation method) is ongoing. Numerical simulations for extreme events in Alderney race (wave height of about 7m) are also in progress while we are waiting new radar and in-situ measurements.