Testing linear marginal stability in stratified shear layers
Testing linear marginal stability in stratified shear layers
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测试分层剪切层的线性边际稳定性
DOI：
10.1017/jfm.2018.79
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发表时间：
2018
影响因子：
3.7
通讯作者：
Colm‐cille P. Caulfield
中科院分区：
文献类型：
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作者：
C. Howland;John Taylor;Colm‐cille P. Caulfield
利用二维Boussinesq分层剪切层的直接数值模拟，研究了最小梯度Richardson数Ri_{m}$对Kelvin-Helmholtz不稳定性向其饱和“波涛”状态演化的影响。即使当背景速度和密度分布的扩散被人工体力抵消以保持初始轮廓时，在$Ri_{m}\rightarrow 1/4$的极限下，扰动增长率趋于零，饱和扰动能量变小。这些结果意味着，至少对于这样的典型弯曲分层剪切流，Ri_{m}$仅略小于1/4的“边缘不稳定”流极不可能成为“顺从”流，即在没有附加外力的情况下，与显著增强的耗散、不可逆混合和背景分布的非平凡修改相关联的特定意义上的顺从流。
We use two-dimensional direct numerical simulations of Boussinesq stratified shear layers to investigate the influence of the minimum gradient Richardson number $Ri_{m}$ on the early time evolution of Kelvin–Helmholtz instability to its saturated ‘billow’ state. Even when the diffusion of the background velocity and density distributions is counterbalanced by artificial body forces to maintain the initial profiles, in the limit as $Ri_{m}\rightarrow 1/4$ , the perturbation growth rate tends to zero and the saturated perturbation energy becomes small. These results imply, at least for such canonical inflectional stratified shear flows, that ‘marginally unstable’ flows with $Ri_{m}$ only slightly less than 1/4 are highly unlikely to become ‘turbulent’, in the specific sense of being associated with significantly enhanced dissipation, irreversible mixing and non-trivial modification of the background distributions without additional externally imposed forcing.