Turbulent mixing by breaking gravity waves
Turbulent mixing by breaking gravity waves
复制标题
通过打破重力波进行湍流混合
DOI：
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发表时间：
1998
影响因子：
3.7
通讯作者：
A. Dörnbrack
中科院分区：
文献类型：
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作者：
A. Dörnbrack
利用高分辨率数值模拟方法研究了重力内波在临界水平以下三维破碎所引起的湍流特性。流动分为三个阶段。在第一个流动是二维的：内部重力波垂直向上传播，并创建一个对流不稳定的临界水平以下的区域。对流不稳定导致第二阶段的湍流破裂。发展中的三维混合区在波传播平面内被组织成剪切驱动的翻转辊，在展向平面内被组织成反向旋转的流向涡。剪切产生的湍动能最大。在最后阶段，剪切的产生和湍流动能的机械耗散达到平衡。流动的演变取决于地形参数（波长和振幅），剪切和分层以及粘度。在这里，只有粘度的不稳定性结构和演变的雷诺数的影响被认为是。较小的粘性导致对流不稳定和翻转波的早期发生。然而，粘度延迟的发病小规模的三维不稳定性，并导致减少动量转移到平均流量低于临界水平。因此，二次翻转辊的形成由较低的粘度维持。计算了总动能和总势能的收支。虽然区域平均湍动能不到总动能的1%，但在临界水平以下，它足以形成斑片状、间歇性的湍流混合层。
The characteristics of turbulence caused by three-dimensional breaking of internal gravity waves beneath a critical level are investigated by means of high-resolution numerical simulations. The flow evolves in three stages. In the first one the flow is two-dimensional: internal gravity waves propagate vertically upwards and create a convectively unstable region beneath the critical level. Convective instability leads to turbulent breakdown in the second stage. The developing three-dimensional mixed region is organized into shear-driven overturning rolls in the plane of wave propagation and into counter-rotating streamwise vortices in the spanwise plane. The production of turbulent kinetic energy by shear is maximum. In the last stage, shear production and mechanical dissipation of turbulent kinetic energy balance. The evolution of the flow depends on topographic parameters (wavelength and amplitude), on shear and stratification as well as on viscosity. Here, only the implications of the viscosity for the instability structure and evolution in terms of the Reynolds number are considered. Smaller viscosity leads to earlier onset of convective instability and overturning waves. However, viscosity retards the onset of smaller-scale three-dimensional instabilities and leads to a reduced momentum transfer to the mean flow below the critical level. Hence, the formation of secondary overturning rolls is sustained by lower viscosity. The budgets of total kinetic and potential energies are calculated. Although the domain-averaged turbulent kinetic energy is less than 1% of the total kinetic energy, it is strong enough to form a patchy and intermittent turbulent mixed layer below the critical level.