Identifying unstable modes in stratified shear layers
Identifying unstable modes in stratified shear layers
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DOI：
10.1063/1.3379845
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发表时间：
2010-05
影响因子：
4.6
通讯作者：
J. Carpenter;N. Balmforth;G. Lawrence
中科院分区：
文献类型：
--
作者：
J. Carpenter;N. Balmforth;G. Lawrence
对分层剪切流中不稳定机制的一种解释是基于两个独立传播的波可能相互作用而导致彼此增长的想法。这一理论在本研究中被用来开发一种可用于识别不同类型的不稳定模式的诊断方法。我们关注的是容易受到开尔文-亥姆霍兹(KH)和Holmboe(H)不稳定模式影响的分层剪切层--尽管公式更一般。在对称层状剪切层(剪切层中心与密度界面重合的地方)中，这种诊断方法对区分KH和H模是有用的。不对称层状剪切层也被研究，因为在这种流动中没有明显的KH型和H型模式的区别。KH增长机制被预测为比对称情况下更强的层结(即更大的体积Richardson数)，与非线性数值结果定性一致。然而，我们发现这一转变是一个渐进的过程，随着本体Richardson数的增加，KH机制让位于H。为了验证该方法的有效性，我们将其应用于在弗雷泽河河口观测到的不稳定性。
One interpretation of the mechanism of instability in stratified shear flows is based on the idea that two independently propagating waves may interact to cause mutual growth in one another. This theory is used in the present study to develop a diagnostic that can be used to identify different types of unstable modes. We focus on stratified shear layers that are susceptible to both the Kelvin–Helmholtz (KH) and Holmboe (H) modes of instability—though the formulation is more general. The diagnostic is found to be useful in differentiating between KH and H modes in the symmetric stratified shear layer (where the center of the shear layer and the density interface coincide). The asymmetric stratified shear layer is also examined since there is no clear distinction between KH- and H-type modes in this flow. The KH mechanism of growth is predicted to extend to stronger stratifications (i.e., larger bulk Richardson numbers) than in the symmetric case, in qualitative agreement with nonlinear numerical results. However, the transition is found to be a gradual one in which the KH mechanism gives way to the H as the bulk Richardson number is increased. In order to demonstrate the utility of the method, we apply it to instability observed in the Fraser River estuary.