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arXiv 1310.2650physics.flu-dyn
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线性流体动力学稳定性稳定性理论中的对称性分析:线性剪切中的经典模式和新模式

Symmetry Analysis in Linear Hydrodynamic Stability Theory: Classical and New Modes in Linear Shear

Andreas Nold, Martin Oberlack

摘要:

本文对二维不可压缩流体的线性剪切流的线性化纳维-斯托克斯方程进行了对称性分类。对称的完整集合被用来系统地导出不变的反函数。对称性分析把握了三种方法。其中两个是现有的,代表经典的正常模式和开尔文模式,而第三个是一种新的方法,并导致一个新的封闭形式的解决方案的旅行模式,表现出质的不同的行为在能量,形状和运动学相比,经典的方法。最后一种模式在无粘情况下是能量守恒的。它们在横流方向上是局部的,在流向方向上是周期性的。至于运动学,它们在横流方向上以恒定速度行进,而在顺流方向上,它们被基流加速。在粘性的情况下,模式预锻,由于高波数贡献的阻尼。

英文摘要:

We present a symmetry classification of the linearised Navier-Stokes equations for a two-dimensional unbounded linear shear flow of an incompressible fluid. The full set of symmetries is employed to systematically derive invariant ansatz functions. The symmetry analysis grasps three approaches. Two of them are existing ones, representing the classical normal modes and the Kelvin modes, while the third is a novel approach and leads to a new closed-form solution of traveling modes, showing qualitatively different behaviour in energetics, shape and kinematics when compared to the classical approaches. The last modes are energy conserving in the inviscid case. They are localized in the cross-stream direction and periodic in the streamwise direction. As for the kinematics, they travel at constant velocity in the cross-stream direction, whilst in the streamwise direction they are accelerated by the base flow. In the viscous case, the modes break down due to damping of high wavenumber contributions.

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