The dynamic coupling between wind and waves within the marine atmospheric boundary layer is a key physical process determining the inflow characteristics, wake evolution, and power generation efficiency of offshore wind turbines. Previous studies have mostly focused on the overall effects of waves on wind farms instead of distinguishing individual processes and the coupling mechanism between them. This study deconstructs the wave effects into contributions from wave steepness and wave age, and investigates their synergistic coupling. We combine large eddy simulation with a moving surface drag model to simulate a 2D parameter space of wave age and wave steepness under typical wind-wave conditions. The chosen parameter space is shown to be representative of real sea states based on ERA5 reanalysis data from China's coastal waters. The results indicate that the effect of changing wave steepness on offshore wind farm wakes and power output is significantly modulated at different wave ages. Under wind-sea-dominated conditions with small wave age, wave steepness is positively correlated with sea surface drag, and an increase in wave steepness suppresses turbine wake recovery, thereby reducing wind farm power output. Conversely, during the large-wave age, increased wave steepness accelerates turbine wake recovery and significantly enhances wind farm power-generation efficiency.
To identify the wave stress effects on wakes, we unify the inflow profiles across different conditions, thereby isolating the long-term wave effect. The results show that the wake differences among conditions are not uniformly distributed vertically but are concentrated in the near-surface region below the turbine’s lower blade tip, with minimal differences in velocity profiles above hub height. These findings suggest that the coupled wave age-steepness parameters must be incorporated into wind resource assessment and energy yield prediction for offshore wind farms.