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arXiv 1907.12932physics.flu-dynmath.DS
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不变解对Hele-Shaw通道中气泡瞬态行为的影响

The influence of invariant solutions on the transient behaviour of an air bubble in a Hele-Shaw channel

J. S. Keeler, A. B. Thompson, G. Lemoult, A. Juel, A. L. Hazel

摘要:

我们假设,动力系统的概念,用于研究过渡到湍流的剪切流是适用于其他过渡现象的流体力学。在本文中,我们考虑了一个有限的气泡内传播的Hele-Shaw通道包含的深度扰动。最近的实验表明,气泡的形状变得更加复杂,量化的瞬态气泡尖端的数量增加,随着流速的增加。最终,气泡改变了拓扑结构,分裂成两个或更多具有非平凡动力学的不同实体。我们表明,定性相似的行为表现出的实验是由先前建立的,深度平均的数学模型,该模型的复杂的解决方案结构的后果。对于研究的气泡体积,一个稳定的不对称的气泡存在的所有感兴趣的流速,而第二个稳定的解决方案的分支发展以上的临界流速和对称和不对称的形状之间的过渡。双稳态区域由第二分支上的两个Hopf分支限定。通过开发一种方法的数值弱非线性稳定性分析,我们表明,不稳定的周期轨道来自在较低的流量的Hopf分岔,而且,这些轨道的边缘状态,影响系统的瞬态行为。

英文摘要:

We hypothesize that dynamical systems concepts used to study the transition to turbulence in shear flows are applicable to other transition phenomena in fluid mechanics. In this paper, we consider a finite air bubble that propagates within a Hele-Shaw channel containing a depth-perturbation. Recent experiments revealed that the bubble shape becomes more complex, quantified by an increasing number of transient bubble tips, with increasing flow rate. Eventually the bubble changes topology, breaking into two or more distinct entities with non-trivial dynamics. We demonstrate that qualitatively similar behaviour to the experiments is exhibited by a previously established, depth-averaged mathematical model; a consequence of the model's intricate solution structure. For the bubble volumes studied, a stable asymmetric bubble exists for all flow rates of interest, whilst a second stable solution branch develops above a critical flow rate and transitions between symmetric and asymmetric shapes. The region of bistability is bounded by two Hopf bifurcations on the second branch. By developing a method for a numerical weakly nonlinear stability analysis we show that unstable periodic orbits emanate from the Hopf bifurcation at the lower flow rate and, moreover, that these orbits are edge states that influence the transient behaviour of the system.

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