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Turbulence and scaling processes in the ocean
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Numerical Study of Atmospheric Turbulence over Ocean Waves
P-P3-07
Zixuan Yang* , St. Anthony Falls Laboratory & Department of Mechanical Engineering, University of Minnesota, USA
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Science, China
Tao Cao, St. Anthony Falls Laboratory & Department of Mechanical Engineering, University of Minnesota, USA
Xuanting Hao, St. Anthony Falls Laboratory & Department of Mechanical Engineering, University of Minnesota, USA
Lian Shen, St. Anthony Falls Laboratory & Department of Mechanical Engineering, University of Minnesota, USA
Presenter Email: yangzx@imech.ac.cn |
| The dynamics of marine atmospheric turbulence is significantly influenced by surface gravity waves. In this study, we investigate the wave effect on wind turbulence in the marine atmospheric boundary layer. In the problem setup, we simulate turbulent air flows over both broadband and monochromatic waves. For the broadband wave fields, we have identified distinct wave signatures in the space-time correlation of wind turbulence by examining the full frequency-wavenumber spectrum; for a monochromatic wave prorogating opposing wind direction, we have observed that the wave coherent structure is characterized by large in-phase wave-induced pressure, which is nearly symmetric with respect to the surface wave crest. It is further found that this in-phase pressure wave fluctuation agrees with the inviscid theory well, indicating a self-similar behavior in the outer region. We also study the wind turbulence over breaking waves. We focus on the effects of wave breaking on the turbulence statistics and structures. We report a high pressure ahead of the wave crest during wave breaking. This finding provides an explanation to why the air flow is not able to see the wave trough during wave breaking, which was believed to be an important factor contributing to the saturation of drag coefficient at high wind speeds, such as in hurricanes. Through the comparison of turbulence statistics at different stages of wave breaking, we discover a magnitude increase of kinetic energy of velocity fluctuations during wave plunging at small and large wave ages, which is attributed to the enhancement of turbulence motion and wave-coherent motion, respectively. However, at an intermediate wave age, such a transient growth of kinetic energy is not observed, which is explained as the absence of significant enhancement of either turbulence motion or wave-coherent motion. This discovery indicates that the wave age needs to be considered in the parametrization of marine atmospheric boundary layer flow with breaking waves. |
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