Stratified turbulent mixing in oscillating shear flows
Stratified turbulent mixing in oscillating shear flows
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振荡剪切流中的分层湍流混合
DOI：
10.1017/jfm.2022.537
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发表时间：
2022
影响因子：
3.7
通讯作者：
Lewin S
中科院分区：
文献类型：
--
作者：
Lewin S
受海洋内波产生的局部剪切变化的启发，我们使用直接数值模拟来研究随时间变化的剪切力对高雷诺数下开尔文-亥姆霍兹不稳定性（KHI）产生的湍流的演化和混合的影响。强制是使用倾斜坐标系来实现的，这会导致背景剪切周期性地加速和减速。我们证明，在不稳定性的发展和剪切振荡周期之间有适当的时间安排，具有减速剪切的 KHI 产生的湍流以与具有恒定背景剪切的流动明显不同的方式混合，特别是从替代来源提取的湍流运动能量。因此，对于剪切减速的流，通过背景势能的变化测量的混合总量实际上可能显着更大，尽管流中的总动能显着较小。这种混合具有与对流驱动流而不是剪切驱动流更共同的特征，支持了触发湍流的机制发生根本变化的论点。
Motivated by the variation of local shear produced by internal waves in the ocean, we use direct numerical simulations to investigate the effect of a time-dependent shear forcing on the evolution and mixing of turbulence produced by Kelvin–Helmholtz instability (KHI) at high Reynolds number. The forcing is implemented using a tilting coordinate system which causes the background shear to accelerate and decelerate periodically. We demonstrate that, with suitable timing between development of instability and the shear oscillation cycle, turbulence produced by KHI with a decelerating shear mixes in a distinctly different way from the flow with constant background shear, specifically with the energy for turbulent motions extracted from alternative sources. As a result, the total amount of mixing as measured by the change in background potential energy can in fact be significantly larger for flows in which the shear is decelerated, despite the fact that the total kinetic energy in the flow is significantly smaller. The mixing has characteristics more in common with convectively driven rather than shear-driven flows, supporting the argument for an underlying change in the mechanisms triggering the turbulence.
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