Elastic wake instabilities in a creeping flow between two obstacles
Elastic wake instabilities in a creeping flow between two obstacles
复制标题
两个障碍物之间蠕动流中的弹性尾流不稳定性
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
V. Steinberg
中科院分区：
文献类型：
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作者：
Atul Varshney;V. Steinberg
研究表明，当通道壁距离圆柱体足够远时，稀聚合物溶液在两个间距较大的圆柱体之间形成阻碍流动的通道流动是无界流动的一个重要范例。在两个大间距圆柱体之间的蠕动粘弹性通道流动中，不稳定性的定量表征揭示了两个弹性驱动的转变，它们与时间反转和镜像对称性的破坏有关：Hopf和正向分岔分别由两个阶参数$mbox{v}_{rms}$和$ar{omega}$描述。我们认为，障碍物之间归一化距离的减小会导致两个分岔崩溃为一个协维-2点，这是许多非平衡系统的一般情况。然而，令人吃惊和意想不到的结果是，在粘弹性流动中，通过在保留流线曲率处增加涡长来增加涡量的机制，这与众所周知的聚合物添加剂对牛顿流中涡量的抑制形成鲜明对比。
It is shown that a channel flow of a dilute polymer solution between two widely spaced cylinders hindering the flow is an important paradigm of an unbounded flow in the case in which the channel wall is located sufficiently far from the cylinders. The quantitative characterization of instabilities in a creeping viscoelastic channel flow between two widely spaced cylinders reveals two elastically driven transitions, which are associated with the breaking of time-reversal and mirror symmetries: Hopf and forward bifurcations described by two order parameters $mbox{v}_{rms}$ and $ar{omega}$, respectively. We suggest that a decrease of the normalized distance between the obstacles leads to a collapse of the two bifurcations into a codimension-2 point, a situation general for many non-equilibrium systems. However, the striking and unexpected result is the discovery of a mechanism of the vorticity growth via an increase of a vortex length at the preserved streamline curvature in a viscoelastic flow, which is in sharp contrast to the well-known suppression of the vorticity in a Newtonian flow by polymer additives.