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arXiv 1503.08240nlin.PSphysics.flu-dyn
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二维流体流动中波前传播的时间障碍

Finite-time barriers to front propagation in two-dimensional fluid flows

John R. Mahoney, Kevin A. Mitchell

摘要:

最近的理论和实验研究已经证明了某些不变流形的作用,称为燃烧不变流形(BIM),作为单向动力学障碍的流动流体中传播的反应前沿。这些屏障在二维流体流动中形成一维曲线。在以前的研究中,流体速度场被要求是时间无关的或时间周期性的。在本研究中,我们开发了一种方法来识别突出的单向障碍,仅基于流体速度数据在有限的时间间隔,这可能具有任意的时间依赖性。我们称这样的障碍燃烧拉格朗日相干结构(bLCS)在类比拉格朗日相干结构(LCS)中常用的被动平流。我们的方法是基于LCS的变分公式,使用Farazmand,Blazevski和Haller在被动平流的背景下引入的固定“拉格朗日切变”曲线[Physica D 278-279,44(2014)]。我们数值验证了我们的技术,证明了bLCS密切跟踪BIM的时间无关,双涡通道流与相反的“风”。

英文摘要:

Recent theoretical and experimental investigations have demonstrated the role of certain invariant manifolds, termed burning invariant manifolds (BIMs), as one-way dynamical barriers to reaction fronts propagating within a flowing fluid. These barriers form one-dimensional curves in a two-dimensional fluid flow. In prior studies, the fluid velocity field was required to be either time-independent or time-periodic. In the present study, we develop an approach to identify prominent one-way barriers based only on fluid velocity data over a finite time interval, which may have arbitrary time-dependence. We call such a barrier a burning Lagrangian coherent structure (bLCS) in analogy to Lagrangian coherent structures (LCSs) commonly used in passive advection. Our approach is based on the variational formulation of LCSs using curves of stationary "Lagrangian shear", introduced by Farazmand, Blazevski, and Haller [Physica D 278-279, 44 (2014)] in the context of passive advection. We numerically validate our technique by demonstrating that the bLCS closely tracks the BIM for a time-independent, double-vortex channel flow with an opposing "wind".

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