Simulation-based study of wave coherent structures and mean profiles of wind opposing waves propagation.

We performed a large-eddy simulation (LES) of turbulent wind opposing water waves. Based on the simulation data, detailed analyses of wave coherent structures and mean profiles were conducted. It is found that the wave coherent structure is characterized by large in-phase wave-induced pressure, which is symmetric with respective to the surface wave crest. The in-phase pressure wave fluctuation agrees with the inviscid theory well, indicating a self-similar behavior in the outer region. The out-of-phase wave-induced pressure is relatively small compared to the in-phase pressure fluctuation, yet crucial to the momentum transfer from wind to wave. It is found that the Reynolds shear stress plays a critical role in the generation of out-of-phase pressure, which is the direct cause for the form drag on the surface waves. We also observed a modification on the mean streamwise velocity by the surface waves, which is related to the large favorable pressure gradient on the windward face of the surface waves, and the correspondingly damped intensity of turbulent vorticity.