LAUSR

Abstract 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 $\tilde {w}$ in the wind on the two sides of the wave crest, while the streamwise velocity $\tilde {u}$ away from the surface and the air pressure $\tilde {p}$ 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 $\tilde {w}$ into an antisymmetric component and a symmetric component. The solution of the antisymmetric component of $\tilde {w}$ 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 $\tilde {w}$ 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 $\tilde {u}$ and $\tilde {p}$. In contrast, the small-magnitude symmetric component of $\tilde {w}$ is forced by the antisymmetric $\tilde {w}$ 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 $\tilde {w}$ causes a slight asymmetry in $\tilde {u}$ and $\tilde {p}$, 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.