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arXiv physics/0510114physics.flu-dynmath.CA
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泰勒-戈尔茨坦方程及其稳定性

Taylor-Goldstein equation and stability

Aravind Banerjee

摘要:

Taylor-Goldstein方程(TGE)控制变密度无粘流体剪切流动的稳定性。它在这里调查从严格的几何的角度来看,使用一个典型的类,其变换。本文推广了Rayleigh拐点判据和Fjortoft均质剪切流不稳定条件,使只有拐点处的剖面才能被密度的变化所修正。这满足了文献中的持续期望。存在一对边界,使得在任何不稳定流动中,流动曲率(流动层的函数)在某些流动层超过上界,而在较高的流动层低于下界。这是这里证明的主要结果。边界上的增长率和波数的不稳定模式,在履行长期的预测霍华德。将Drazin和Howard关于波数有界性的一个结果推广到TGE。如果在流动中的任何地方局部Richardson数不超过1/4,则上述结果成立,否则可以看到不稳定性所需条件的减弱。得到了中性稳定波传播的条件和不稳定波相速度的界。研究还表明,任意流动简正波的复波速度集是有界的。得到了TGE的基本解,并检验了它们的光滑性。最后给出了不稳定性的充分条件。

英文摘要:

Taylor-Goldstein equation (TGE) governs the stability of a shear-flow of an inviscid fluid of variable density. It is investigated here from a rigorous geometrical point of view using a canonical class of its transformations. Rayleigh's point of inflection criterion and Fjortoft's condition of instability of a homogenous shear-flow have been generalized here so that only the profile carrying the point of inflection is modified by the variation of density. This fulfils a persistent expectation in the literature. A pair of bounds exists such that in any unstable flow the flow-curvature (a function of flow-layers) exceeds the upper bound at some flow-layer and falls below the lower bound at a higher layer. This is the main result proved here. Bounds are obtained on the growth rate and the wave numbers of unstable modes, in fulfillment of longstanding predictions of Howard. A result of Drazin and Howard on the boundedness of the wave numbers is generalized to TGE. The results above hold if the local Richardson number does not exceed 1/4 anywhere in the flow, otherwise a weakening of the conditions necessary for instability is seen. Conditions for the propagation of neutrally stable waves and bounds on the phase speeds of destabilizing waves are obtained. It is also shown that the set of complex wave velocities of normal modes of an arbitrary flow is bounded. Fundamental solutions of TGE are obtained and their smoothness is examined. Finally sufficient conditions for instability are suggested.

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