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Turbulence and scaling processes in the ocean
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Wave-Turbulence Interaction in the Upper-Ocean Boundary Layer
Tuesday 8th @ 1010-1030, Conference Room 4
Bing-Qing Deng, St Anthony Falls Laboratory and Department of Mechanical Engineering, University of Minnesota, USA
Anqing Xuan, St Anthony Falls Laboratory and Department of Mechanical Engineering, University of Minnesota, USA
Tianyi Li, St Anthony Falls Laboratory and Department of Mechanical Engineering, University of Minnesota, USA
Lian Shen* , St Anthony Falls Laboratory and Department of Mechanical Engineering, University of Minnesota, USA
Presenter Email: lianshen@gmail.com |
| The turbulent flow in the upper ocean is an interactive process that involves waves, current and turbulence. Surface waves can significantly modify the characteristics of the turbulence in the ocean surface boundary layer, resulting in features such as Langmuir circulation and front filaments. In this study, we use advanced wave-phase-resolved simulation methods to simulate the Langmuir circulation under both the monochromatic and broadband surface waves, and investigate the wave effect on the turbulence underneath. For the monochromatic wave, we focus on the mechanisms of the turbulence distortion by the wave. It is found that the turbulence coherent structures and statistics vary with the wave phase as a result of the straining of wave orbital velocity. Further analyses of the vorticity dynamics and turbulence kinetic energy budget reveal that both the phase-averaged wave effect and the correlation between the wave phase and turbulence are important to the generation and evolution of Langmuir circulation. We have also developed a wave-directly-forcing method based on the Helmholtz’s decomposition for accurate and efficient simulations of Langmuir circulation under realistic ocean conditions with broadband waves. The windrows generated by Langmuir circulation in the simulation agree with those observed by marine radars deployed in field. The upper-ocean boundary layer also features many submesoscale structures such as front filaments. These inhomogeneous structures interact with the boundary-layer turbulence and surface waves, leading to more complex dynamic processes. To study the upper ocean in the presence of a front filament, we use large-eddy simulation to capture the evolution of a submesoscale front filament and resolve the boundary-layer turbulence eddies at the same time. The influence of the filament on the surface wave is also investigated using our in-house phase-resolved wave simulation tool, which can simulate accurately and efficiently the nonlinear ocean waves above complex ocean currents. It is found that the sharp change of current velocity across the front filament generates a boundary separating smooth and rough ocean surface regions. |
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