Motion of Passive Scalar by Elasticity-Induced Instability in Curved Microchannel
Motion of Passive Scalar by Elasticity-Induced Instability in Curved Microchannel
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DOI：
10.1155/2014/734175
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发表时间：
2014-08
影响因子：
2.1
通讯作者：
Xiaobin Li;Hongna Zhang;Yang Cao;M. Oshima;Feng-chen Li
中科院分区：
文献类型：
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作者：
Xiaobin Li;Hongna Zhang;Yang Cao;M. Oshima;Feng-chen Li
本文采用直接数值模拟方法对曲线微通道中弹性诱导的不规则流动、被动混合和标量演化进行了研究。在由弹性不稳定性引起的低雷诺数混沌流中实现了混合增强。在混合过程中，流动所携带的被动标量输运受到流动结构以及粘弹性流体微观结构与流动结构本身相互作用的很大影响。对大范围的粘弹性进行了模拟。当弹性效应超过临界值时，流动趋于混沌状态，而标量的演化变得强烈和快速，与实验结果吻合良好。对于标量梯度的时间变化，它们以等值面的形式迅速变化，在体中呈“卷”状，在壁面附近演变成“线”状。这表明流场应该与粘弹性微分子的变形有关。微分子变形与流场变形的概率分布函数分析表明，分子拉伸的主要方向与流场变形的主要方向垂直。这意味着由于通道壁的限制，它们之间的相关性较弱。
This paper presented a direct numerical simulation (DNS) study on the elasticity-induced irregular flow, passive mixing, and scalar evolution in the curvilinear microchannel. The mixing enhancement was achieved at vanishingly low-Reynolds-number chaotic flow raised by elastic instabilities. Along with the mixing process, the passive scalar transportation carried by the flow was greatly affected by the flow structure and the underlying interaction between microstructures of viscoelastic fluid and flow structure itself. The simulations are conducted for a wide range of viscoelasticity. As the elastic effect exceeds the critical value, the flow tends to a chaotic state, while the evolution of scalar gets strong and fast, showing excellent agreement with experimental results. For the temporal changing of scalar gradients, they vary rapidly in the form of isosurfaces, with the shape of “rolls” in the bulk and evolving into “threads” near the wall. That indicates that the flow fields should be related to the deformation of viscoelastic micromolecules. The probability distribution function analysis between micromolecular deformation and flow field deformation shows that the main direction of molecular stretching is perpendicular to the main direction of flow field deformation. It implies they are weakly correlated, due to the confinement of channel wall.