Relationship Between Macroscopic Rheological Properties and Microstructure of a Dilute Suspension by a Two-Way Coupling Numerical Scheme
Relationship Between Macroscopic Rheological Properties and Microstructure of a Dilute Suspension by a Two-Way Coupling Numerical Scheme
复制标题
通过双向耦合数值方案研究稀悬浮液宏观流变特性与微观结构之间的关系
DOI：
10.1115/ajkfluids2019-5449
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
K. Morinishi
中科院分区：
文献类型：
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作者：
T. Fukui;M. Kawaguchi;K. Morinishi
悬浮液的流变性取决于颗粒的形状、颗粒的空间排列和流体动力相互作用以及颗粒的浓度。到目前为止，我们提出了一种双向耦合的数值格式来评估颗粒旋转对流变性的影响。这种粒子旋转会降低流体阻力。然而，这些研究是在悬浮颗粒均匀分布的条件下进行的。因此，为了更好的实际应用，本研究中的颗粒被随机分散在悬浮液中。通过压力驱动的悬浮液流动模拟，考虑了惯性对颗粒空间排列与悬浮液流变性之间关系的影响。流道宽度和轴向长度分别设置为400μm和1620μm，流动方向采用周期边界条件。将直径为20μm的刚性球形颗粒随机分散在流道中作为初始条件。将悬浮液浓度设定为1.02%作为稀释假设，再现了雷诺数为2~128的悬浮流，考察了悬浮颗粒对流体流变性的惯性影响。用幂指数(非牛顿指数)评价了悬浮液的流变性。在低雷诺数条件下，悬浮体的速度分布几乎呈抛物线分布。这表明悬浮液表现为牛顿流体。另一方面，对于较高的雷诺数条件，颗粒上的升力增大，并向平衡的y轴位置迁移，在该位置，升力为零。颗粒y轴位置的这些变化导致了悬浮液的微观结构的变化，随后是宏观流变性的变化。由于这些微观结构的变化，非牛顿(触变)性质随着雷诺数的增加而增强。
The rheological properties of a suspension depend on particle shape, spatial arrangement of the particles and hydrodynamic interactions as well as the concentration of the particles. So far, we proposed a two-way coupling numerical scheme to evaluate the effects of particle rotation on the rheological properties. This particle rotation decreases the fluid resistance. However, these studies were conducted on the condition that suspended particles were homogeneously distributed. Therefore, the particles in this study are randomly scattered in a suspension for better practical applications. Pressure-driven suspension flow simulations were conducted to consider the effects of inertia on the relationship between spatial arrangement of the particles and the rheological properties of a suspension. The channel width and axial length were set 400 μm and 1620 μm, respectively, and periodic boundary conditions were applied in the flow direction. The rigid spherical particles whose diameter was 20 μm were randomly scattered in the channel as an initial condition. The concentration of the suspension was set 1.02% for dilute assumption, and the suspension flows with the Reynolds number from 2 to 128 were reproduced in order to investigate the inertial effects of the suspended particles on the rheological properties. The rheological properties of the suspension were evaluated in terms of power-law index (non-Newtonian index). The velocity profile of a suspension for low Reynolds number conditions exhibited almost parabolic. This indicates the suspension behaves as a Newtonian fluid. For higher Reynolds number conditions, on the other hand, the lift force on the particles increased and they migrated toward the equilibrium y-axis position, where the lift force is zero. These changes in the y-axis position of the particles caused a change in microstructure of the suspension, which were followed by a change in macroscopic rheological properties. Owing to these microstructure changes, the non-Newtonian (thixotropic) properties were enhanced as the Reynolds number increased.