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首页> 外文期刊>Journal of Physical Oceanography >Numerical Investigation of Solitary Internal Wave-Induced Global Instability in Shallow Water Benthic Boundary Layers
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Numerical Investigation of Solitary Internal Wave-Induced Global Instability in Shallow Water Benthic Boundary Layers

机译：浅水底边界层内孤立波引起的整体失稳的数值研究

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The time-dependent boundary layer induced by a weakly nonlinear solitary internal wave in shallow water is examined through direct numerical simulation. Waves of depression and elevation are both considered. The mean density field corresponds to that typical of the coastal ocean and lakes where the lower fraction of the water column is subject to the stabilizing effect of a diffuse stratification. Sufficient resolution of the "inviscid" dynamics of the boundary layer is ensured through use of a Legendre spectral multidomain discretization scheme in the vertical direction. At higher Reynolds numbers, where the simulations become underresolved, because of restrictions in available computational resources, spectral accuracy and numerical stability at the scales of physical interest are preserved through use of a penalty scheme in the vertical and explicit spectral filtering. Thus, a highly accurate description of the qualitative dynamics of the wave-induced global instability is possible and finescale physical mechanisms critical to the appearance of this instability are not smeared out by the high artificial dissipation inherent in lower-order finite-difference schemes. Results indicate that, for a wave amplitude exceeding a critical value, the global instability occurs in regions near the bottom boundary where the wave induces an adverse pressure gradient. The structure of the associated separation bubble is modified through the establishment of coherent and synchronous dynamics, characterized by elevated levels of bottom shear stress and a periodic shedding of coherent vortex structures. Although details of the vortex shedding depend on the particular wave forcing involved, these vortical structures always ascend high into the water column. All findings suggest that this global instability is a potent mechanism for benthic turbulence, mixing, and possible sediment resuspension in shallow waters, presumably even more intense than the nominal turbulent boundary layer.
机译：通过直接数值模拟研究了由弱非线性孤立内波在浅水中引起的随时间变化的边界层。都考虑了沮丧和抬高的浪潮。平均密度场对应于沿海海洋和湖泊的典型密度场，在该区域中，水柱的下半部分受到弥散分层的稳定作用。通过在垂直方向上使用勒让德谱多域离散化方案，可以确保边界层“无形”动力学的足够分辨率。在较高的雷诺数下，由于可用计算资源的限制，导致模拟无法充分解决，因此通过在垂直和显式光谱滤波中使用惩罚方案，可以保留物理精度尺度上的光谱精度和数值稳定性。因此，可以高度精确地描述波动引起的整体不稳定性的定性动力学，而且对于这种不稳定性的出现至关重要的精细物理机制不会因低阶有限差分方案中固有的高人工耗散而被抹去。结果表明，对于超过临界值的波幅，全局不稳定性发生在波引起不利压力梯度的底边界附近区域。通过建立相干和同步动力学来修改相关的分离气泡的结构，其特征在于底部剪切应力的水平升高和相干涡结构的周期性脱落。尽管旋涡脱落的细节取决于所涉及的特定波浪力，但这些旋涡结构始终会上升到水柱中。所有发现均表明，这种全球不稳定性是底流湍流，混合和可能的沉积物在浅水区重悬浮的有效机制，据推测其甚至比名义湍流边界层还要强烈。

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