分层射流与壁面效应
Stratified jet with wall effects
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中文总结 AI 辅助
本研究通过壁面约束的Bickley射流模型，揭示了分层流中短波不稳定性引发平均流不对称、长波结构发射内重力波并显著降低射流速度，且发现一种不依赖壁面、超越Miles-Howard判据的粘性不稳定模式。
中文摘要 AI 辅助
分层流中的射流在地球物理学中普遍存在。一个基本问题是，流动产生的不稳定性和相干结构是否与物理边界相互作用，如果是，又是如何相互作用的。为此，我们采用了一个简单的典型模型流动：在均匀分层流体中，一个平行Bickley射流被限制在壁面之间。我们首先证明，短波长的开尔文-亥姆霍兹不稳定性可以在平均流中产生不对称性。尽管波动在远离射流处迅速衰减，但不对称的平均流并不会衰减。然后，我们研究了能够发射内重力波的长波长相干结构，这些波向壁面缓慢衰减，或者在某些情况下，从射流向外辐射。这些波传输动量并使平均流变形，显著降低了射流中心线速度。当发生辐射时，不稳定性在高雷诺数下是否持续存在，强烈依赖于壁面处施加的边界条件。此外，我们发现了一种不稳定性及其相关的非线性相干结构，它们存在于高于Miles-Howard判据的理查森数下。这种粘性模式的存在并不依赖于壁面的存在。
英文摘要
Jets in stratified flows are ubiquitous in geophysics. A fundamental question is whether the instabilities and coherent structures generated by the flow interact with the physical boundaries and, if so, how. To this end, a simple canonical model flow is employed: a parallel Bickley jet confined between walls in a uniformly stratified fluid. We first show that short wavelength Kelvin-Helmholtz instability can generate asymmetry in the mean flow. Although the fluctuations decay rapidly away from the jet, the asymmetric mean flow does not. We then examine long-wavelength coherent structures that can emit internal gravity waves, which decay slowly towards the walls or, in some cases, radiate away from the jet. These waves transport momentum and distort the mean flow, reducing the jet centreline velocity significantly. When radiation occurs, whether the instability persists at high Reynolds numbers depends strongly on the boundary conditions imposed at the walls. Moreover, we found an instability and associated nonlinear coherent structures that persist at Richardson numbers above the Miles-Howard criterion. The existence of this viscous mode does not rely on the presence of the walls.
