Application of a moving surface drag model to multiscale ocean surfaces

Accurately representing wind-wave interactions in large eddy simulations (LES) of the marine atmospheric boundary layer (MABL) is essential for improving climate models and optimizing offshore operations. The recently proposed MOving Surface Drag (MOSD) model enables cost-effective wall-modeled LES to capture phase information and momentum transfer from waves to turbulent airflow. This model enhances the surface gradient-based wall model by computing pressure drag from ideal potential flow interacting with the moving surface, approximated as piece-wise ramp flow, while unresolved waves are modeled using the standard equilibrium wall model. This study introduces extensions that include local unsteady effects due to time-dependent wave slopes and demonstrates the MOSD model's robustness and accuracy in predicting momentum transfer under a broad range of wind-wave conditions. Using LES with the MOSD model we simulate neutral atmospheric flow over various ocean wavefields generated based on a JONSWAP spectrum. The results are shown to closely match first-order turbulent statistics from more intensive simulations and the contributions of unsteady effects are quantified. The results show that using LES with the MOSD wall-model provides a cost-effective means to introduce realistic ocean wavefield effects onto MABL simulations and thus constitutes a practical method for incorporating wave effects in wind energy studies.