Department of Mechanical Engineering, University of Washington, WA 98195, USA.
Department of Mechanical Engineering, University of Washington, WA 98195, USA and Micro/Bio/Nanofluidics Unit, Okinawa Institute of Science and Technology, Onna, Okinawa 904-0495, Japan.
Soft Matter. 2016 Oct 26;12(42):8666-8681. doi: 10.1039/c6sm01597b.
Wormlike micellar (WLM) solutions are frequently used in enhanced oil and gas recovery applications in porous rock beds where complex microscopic geometries result in mixed flow kinematics with strong shear and extensional components. Experiments with WLM solutions through model microfluidic porous media have revealed a variety of complex flow phenomena, including the formation of stable gel-like structures known as a Flow-Induced Structured Phase (FISP), which undoubtedly play an important role in applications of WLM fluids, but are still poorly understood. A first step in understanding flows of WLM fluids through porous media can be made by examining the flow around a single micro-scale cylinder aligned on the flow axis. Here we study flow behavior of an aqueous WLM solution consisting of cationic surfactant cetyltrimethylammonium bromide (CTAB) and a stable hydrotropic salt 3-hydroxy naphthalene-2-carboxylate (SHNC) in microfluidic devices with three different cylinder blockage ratios, β. We observe a rich sequence of flow instabilities depending on β as the Weissenberg number (Wi) is increased to large values while the Reynolds number (Re) remains low. Instabilities upstream of the cylinder are associated with high stresses in fluid that accelerates into the narrow gap between the cylinder and the channel wall; vortex growth upstream is reminiscent of that seen in microfluidic contraction geometries. Instability downstream of the cylinder is associated with stresses generated at the trailing stagnation point and the resulting flow modification in the wake, coupled with the onset of time-dependent flow upstream and the asymmetric division of flow around the cylinder.
蠕虫状胶束（WLM）溶液常用于增强油气采收率的应用中，在多孔岩床中，复杂的微观几何形状导致混合流动动力学具有较强的剪切和拉伸分量。通过模型微流道多孔介质对 WLM 溶液进行的实验揭示了多种复杂的流动现象，包括形成稳定的凝胶状结构，称为流致结构化相（FISP），这无疑在 WLM 流体的应用中起着重要作用，但仍未被充分理解。通过研究单个微尺度圆柱沿流动轴对齐时的流动情况，可以了解 WLM 流体通过多孔介质的流动。在这里，我们研究了由阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）和稳定的助溶剂 3-羟基萘-2-羧酸（SHNC）组成的水溶液 WLM 在具有三个不同圆柱阻塞比β的微流道装置中的流动行为。我们观察到了丰富的流动不稳定性序列，这取决于β随着 Weissenberg 数（Wi）增加到较大值，而雷诺数（Re）保持较低。圆柱上游的不稳定性与加速进入圆柱和通道壁之间狭窄间隙的流体中的高应力有关；上游的涡旋生长类似于在微流道收缩几何中看到的情况。圆柱下游的不稳定性与尾驻点产生的应力以及尾流中的流动变化有关，这与上游的时变流的开始和圆柱周围的流动不对称分配有关。
