Simulation-based study of wind-wave interaction

We use a suite of advanced numerical tools developed in house to investigate the physical processes in three canonical wind-wave interaction problems. First, we use DNS to investigate the sheltering effect of a long wave on a short wave. It is found that in the presence of the long wave the form drag of the short wave decreases, with the magnitude of the reduction depending on the wave age of the long wave. We also observe that the surface friction is highly correlated to the streamwise vorticity upstream. Next, we study the effect of wave breaking on the wind turbulence. We focus on analyzing small-scale flow physics near the wave surface and the influence of wave breaking on turbulence statistics. It is found that plunging breakers induce acceleration of the air flow near the wave surface. During wave plunging, a large spanwise vortex is generated, which enhances the turbulence mixing around it, and induces large magnitude of turbulent kinetic energy. In the final part, results are presented for wind over broad-band waves in realistic ocean settings. By examining the full wavenumber-frequency spectrum of the turbulent wind, we have identified distinct wave signatures in the space-time correlation of wind turbulence. In the evolution of the wave field, its inner physical process known as the four-wave interaction dominates over wind input, as shown in the frequency downshift phenomenon of the wave field throughout the numerical experiments.