A simulation-based mechanistic study of turbulent wind blowing over opposing water waves

We perform large-eddy simulation (LES) and theoretical analysis to investigate the effects of opposing waves on overlying turbulent wind. The LES results show that opposing waves induce nearly antisymmetric vertical velocity in the wind on the two sides of the wave crest, while the streamwise velocity away from the surface and the air pressure seem symmetric. To study the mechanisms for the wave-induced airflow, we develop a viscous model by linearising the phase-averaged Navier-Stokes equations in the mapped computational curvilinear coordinate. To illustrate the flow dynamics, we split into an antisymmetric component and a symmetric component. The solution of the antisymmetric component of from the viscous curvilinear model agrees well with the LES results for different opposing wave conditions. According to the viscous curvilinear model, the large-magnitude antisymmetric component of is driven by the wave kinematics at the surface and amplified by the mean shear and viscous stress in the air, and it causes the strong symmetric components of and. In contrast, the small-magnitude symmetric component of is forced by the antisymmetric through viscous and turbulent stresses near the surface, and it can be described by a further simplified inviscid curvilinear model away from the surface. It is discovered that the weak symmetric causes a slight asymmetry in and, and generates a mean wave-coherent stress and the form drag on the wave surface. The wave attenuation rates quantified using the form drag agree with the published experiments.