Wall-modeled Large Eddy Simulation of wave effects in offshore wind farms *

In the context of offshore wind farms, accurate predictions of surface fluxes in the marine atmospheric boundary layer are critical for Large Eddy Simulations (LES) of airflow over waves. The effect of the waves on the airflow is often modeled by prescribing roughness length scales in the framework of Monin-Obukhov similarity theory. However, such approaches lack generalizability over different wave conditions due to reliance on model coefficients tuned to specific datasets. Wave phase-resolving simulations on the other hand have higher accuracy but also a higher computational cost. In this work, a sea surface-based hydrodynamic drag model applicable to moving surfaces is developed to model the pressure-based surface drag felt by the wind due to the waves in wall-modeled LES. An offshore wind farm configuration is simulated using a using wall-modeled LES, with the effect of the waves represented using the wave drag model and the wind turbines represented by an actuator disk model.  A variety of sea-state conditions are tested taking advantage of the significantly lower computational cost of the wave model. The effect of the waves on the mean velocity profiles and power production in different wind farm configurations are quantified.