Numerical Simulation Of The Upper Ocean Affected By Wave Breaking And Bubbles

The upper ocean,close to the lower atmospheric boundary layer,plays an important role in sea-air interactions and may significantly affect the exchange of momentum,heat and materials between the ocean and air.The response of the upper ocean to different wind and wave conditions is a research focus in oceanography.This paper reviewed the research status of the upper ocean and chose three important dynamic processes as the objectives:Langmuir circulation,wave breaking and ocean bubbles.In this paper,the traditional wind stress model was combined with a breaker model based on the conservation of momentum and kinetic energy transfer between the ocean and air.Wave breaking,instead of wind stress,becomes the main source to the upper ocean in this new LES model.The bubble concentration model was chosen to simulate the generation and development of ocean bubbles and the gas exchange,whose requirement for grid resolution is much lower than multi-phase model.The flow structures under a single breaker were analyzed in this paper.The results agreed well with experimental data,which means the breaker model can be used to finely reproduce the effect of wave breaking.In this model,the strength factor controls the intensity and propagation speed of vortex and the increase of depth factor may deepen the affected area of dominant vortexBased on the previous work,the new upper ocean model was used to conduct several numerical experiments at medium to high wind speeds.Results show that wave breaking can significantly increase the instability of flow field and the strength of turbulence.Turbulent dissipation rate near water surface is about one magnitude larger than results from traditional wind stress model.Turbulent kinetic energy decays slowly with depth at high wind speeds,which suggests the deepening of mixed layer However,dissipation rate decreases rapidly under same conditions.The development and distribution of ocean bubbles were also simulated in this paper.Large bubbles leave the water in several seconds while smaller bubbles affected by downwelling current remain for a long time.Ocean bubbles mainly distribute in the water near surface and the downward branches of Langmuir circulations.Due to the hydrostatic pressure and surface tension,gases inside bubbles are able to slightly dissolve although the water is saturated.