Impact of Wind-Wave Coupling on Turbulence and Air-Sea Fluxes: Insights From Direct Numerical Simulations

Accurate prediction of air-sea fluxes hinges on a deep understanding of wind-wave interactions, yet feedback mechanisms involving surface waves and wind are not fully understood. This paper investigates the effect of two-way coupling between wind and waves on wind turbulence through direct numerical simulation of air-water two-phase flows, with simulations of non-coupling cases for wind sea and swell. Compared to the uncoupled model, the dissipation of surface waves absorbs momentum from the wind for a wind sea, reducing turbulence intensity, which decreases momentum and heat transfer coefficients (C_D and C_H). In a swell scenario, a wave-driven wind jet produces strong shear and changes interfacial dynamics under coupled conditions, enhancing turbulence intensity within the wave boundary layer. Air-water interaction fosters a positive feedback loop between wind and swells, leading to a consequent increase in C_D and C_H. Parameterizations of C_D and C_H need to account for the wind-wave coupling.