Viscoelastic instabilities in micro-scale flows
Viscoelastic instabilities in micro-scale flows
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DOI：
10.1016/j.expthermflusci.2014.03.004
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发表时间：
2014-11-01
影响因子：
3.2
通讯作者：
Pinho, Fernando T.
中科院分区：
文献类型：
--
作者：
Galindo-Rosales, Francisco J.;Campo-Deano, Laura;Pinho, Fernando T.
许多人工和天然流体含有赋予流体复杂流动行为的大分子、颗粒或液滴。这种复杂的行为导致了应力和变形之间的非线性关系，介于理想粘性液体的牛顿粘性定律和理想弹性材料的胡克定律之间。这种非线性粘弹性行为破坏了蠕动流动条件下流动的可逆性，如在微观尺度上遇到的那样，并可能导致流动不稳定。这些不稳定性为在混沌平流不可行的条件下发展需要不稳定流动的系统提供了另一种选择。粘弹性流体流动的特征是Weissenberg(Wi)和Reynolds(Re)数，在微观尺度上，流动不稳定性发生在Wi-Re空间中宏观上无法达到的区域，即高Wi和低Re。在本文中，我们回顾了作者最近关于具有强伸展分量的流动中的弹性不稳定性的实验工作，这些流动包括：通过双曲线收缩然后突然膨胀的流动；在微流控二极管和流动聚焦装置中的流动；绕受限圆柱体的流动；通过多孔介质的流动和简化的多孔介质模拟。这些流动表现出不同类型的流动转变，取决于几何形状，Wi和Re，包括：从定常对称流动到定常非对称流动的转变，通常紧接着第二次转变为高Wi下的非定常流动；定常对称流动和非定常流动之间的直接转变。(C)2014 Elsevier Inc.保留所有权利。
Many artificial and natural fluids contain macromolecules, particles or droplets that impart complex flow behavior to the fluid. This complex behavior results in a non-linear relationship between stress and deformation standing in between Newton's law of viscosity for an ideal viscous liquid and Hooke's law for an ideal elastic material. Such non-linear viscoelastic behavior breaks down flow reversibility under creeping flow conditions, as encountered at the micro-scale, and can lead to flow instabilities. These instabilities offer an alternative to the development of systems requiring unstable flows under conditions where chaotic advection is unfeasible. Flows of viscoelastic fluids are characterized by the Weissenberg (Wi) and Reynolds (Re) numbers, and at the micro-scale flow instabilities occur in regions in the Wi-Re space typically unreachable at the macro-scale, namely high Wi and low Re. In this paper, we review recent experimental work by the authors on the topic of elastic instabilities in flows having a strong extensional component, including: flow through a hyperbolic contraction followed by a sudden expansion; flow in a microfluidic diode and in a flow focusing device; flow around a confined cylinder; flow through porous media and simplified porous media analogs. These flows exhibit different types of flow transitions depending on geometry, Wi and Re, including: transition from a steady symmetric to a steady asymmetric flow, often followed by a second transition to unsteady flow at high Wi; direct transition between steady symmetric and unsteady flows. (C) 2014 Elsevier Inc. All rights reserved.