蠕虫状胶束溶液绕单个及两个垂直排列微圆柱流动中的弹性不稳定性与分岔：阻塞比和间隙比的影响
Elastic instabilities and bifurcations in flows of wormlike micellar solutions past single and two vertically aligned microcylinders: Effect of blockage and gap ratios
AI总结：
本文采用双组分 VCM 模型数值模拟蠕虫状胶束溶液绕单、双微圆柱的蠕动流，揭示阻塞比、柱间距、Weissenberg 数及参数 ξ 对弹性分岔和流动状态的影响，并解释多孔介质中优先流道形成。
摘要：
本研究基于双组分 Vasquez-Cook-McKinley（VCM）本构模型，对蠕动流状态下微通道中蠕虫状胶束溶液绕单个微圆柱以及两个垂直排列微圆柱的流动特性进行了广泛的数值研究；该模型同时考虑了胶束的断裂和重构动力学。对于单个微圆柱情形，随着阻塞比（圆柱直径与通道高度之比）逐渐变化，我们发现系统中存在流动分岔，并且流动由稳态转变为非稳态。对于两个微圆柱情形，随着两圆柱之间柱间距的变化，我们观察到系统中存在三种不同的流动状态，即发散（D）状态、非对称发散（AD）状态和汇聚（C）状态。近期关于蠕虫状胶束溶液的实验中也观察到了类似类型的流动状态。然而，我们表明，无论是单微圆柱情形下从一种流动状态到另一种流动状态的转变，还是双微圆柱情形下任一流动状态的出现，都强烈依赖于 Weissenberg 数以及非线性 VCM 模型参数 ξ 的取值；该参数本质上表示胶束断裂的难易程度。基于本文针对单微圆柱和双微圆柱给出的结果与讨论，我们最终解释了黏弹性流体在蠕动流状态下穿过多孔介质流动过程中优先路径或通道的形成，这一现象在此前许多实验中均有观察到。
英文摘要：
This study presents an extensive numerical investigation on the flow characteristics of wormlike micellar solutions past a single and vertically aligned two microcylinders placed in a microchannel in the creeping flow regime on the two-species Vasquez-Cook-McKinley (VCM) constitutive model, which takes into account both the breakage and reformation dynamics of micelles. For the case of single microcylinder, as the blockage ratio (ratio of the cylinder diameter to that of the channel height) is gradually varied, we find the existence of a flow bifurcation in the system, and also flow transits from steady to unsteady state. For the case of two microcylinders, we observe the presence of three distinct flow states in the system, namely, diverging (D), asymmetric-diverging (AD) and converging (C) states as the intercylinder spacing in between the two cylinders is varied. Similar types of flow states are also observed in the recent experiments dealing with wormlike micellar solutions. However, we show that either this transition from one flow state to another in the case of a single microcylinder or the occurrence of any flow state in the case of two microcylinders, is strongly dependent upon the values of the Weissenberg number and the nonlinear VCM model parameter ξ, which basically indicates how easy or hard to break a micelle. Based on the results and discussion presented herein for the single and two microcylinders, we ultimately provide the explanation for the formation of preferential paths or lanes during the flow of viscoelastic fluids through a porous media, which was seen in many prior experiments in the creeping flow regime.
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