Characteristics of Wave Breaking and Blocking by Spatially Varying Opposing Currents

A Reynolds-Averaged Navier-Stokes (RANS) flow solver with a Volume of Fluid (VOF) surface capturing scheme is used to investigate wave breaking and blocking due to strong opposing currents. The Shear Stress Transport (SST) k-omega model is modified in order to capture the turbulence properly. The unique capability of the RANS-VOF model allows us to reveal the distinct features of current-induced wave breaking and blocking. The limiting wave steepness at breaking onset is reduced considerably by the opposing current from the Stokes' limit for stationary waves. Although the wave height grows faster before breaking under a more rapidly varying current, the maximum height at the breaking onset remains almost the same. The locations of incipient breaking are slightly shifted downstream/upwave by the increased current gradient. It was found that the wave radiation stress alters the mean water level by competing with the pressure gradient arising from the current-induced surface tilting. The wave set-down and set-up is more pronounced for more intensive breakers occurring under a larger incident wave and current gradient. Our model results indicate an undertow-like change to the current profile due to wave breaking. The turbulence and vorticity generated by the current-induced breaking wave persist and are advected downstream and interact with those generated by the following wave and current.