Simple shear flow of suspensions of elastic capsules
Simple shear flow of suspensions of elastic capsules
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DOI：
10.1007/s001620050003
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发表时间：
2000-02-01
影响因子：
3.4
通讯作者：
Pozrikidis, C
中科院分区：
文献类型：
--
作者：
Breyiannis, G;Pozrikidis, C
在雷诺数消失的极限下，在胶囊所包围的流体的粘度等于环境流体的粘度的特殊情况下，研究了由弹性膜包围的二维胶囊的均匀悬浮液的简单剪切流。采用斯托克斯流界面动力学方法进行动力学模拟，研究了圆形、椭圆形和双凹形无应力胶囊的变形及其无限稀和中等密度悬浮液的流变和统计特性。在初步研究中，悬浮在无限流体中的孤立胶囊的行为被研究为无量纲膜弹性数的函数，该弹性数表示胶囊的变形能力或剪切流的强度。研究发现，临界弹性数不存在，超过该临界弹性数，胶囊会表现出持续伸长，并且无论剪切速率有多大，都会达到平衡构型，这与之前的三维流动结果一致。在胶囊经历相同程度的变形时，二维和三维流动的弹性数之间建立了对应关系。成对胶囊拦截的模拟揭示了与具有均匀表面张力的液滴所表现出的行为类似的行为。由于二维斯托克斯流中存在强烈的流体动力相互作用，在没有流体惯性的情况下，无限稀释极限下的流体动力扩散率的概念是不明确的。双周期单分散悬浮液的动力学模拟，每个周期单元中分布有多达 50 个胶囊，面积分数为 0.25 和 0.40，提供了有关悬浮液的有效流变特性和颗粒运动统计推进力性质的信息。发现流动的特性介于液滴和刚性颗粒之间，这归因于膜的可变形性和界面执行罐踩踏运动的能力。结果与血流流变测量结果进行比较，具有良好的一致性。
The simple shear flow of homogeneous suspensions of two-dimensional capsules enclosed by elastic membranes is studied in the limit of vanishing Reynolds number, in the special case where the viscosity of the fluid enclosed by the capsules is equal to the viscosity of the ambient fluid. The deformation of capsules with circular, elliptical, and biconcave unstressed shapes, and the rheological and statistical properties of their infinitely dilute and moderately dense suspensions are investigated by dynamical simulation using the method of interfacial dynamics for Stokes flow. In a preliminary investigation, the behavior of solitary capsules suspended in an infinite fluid is studied as a function of the dimensionless membrane elasticity number expressing the capsule deformability or the strength of the shear flow. It is found that a critical elasticity number above which a capsule exhibits continued elongation does not exist, and an equilibrium configuration is reached no matter how large the shear rate, in agreement with previous results for three-dimensional flow. A correspondence is established between the elasticity numbers for two- and three-dimensional flow at which the capsules undergo the same degree of deformation. Simulations of pairwise capsule interceptions reveal behavior similar to that exhibited by liquid drops with uniform surface tension. Because of strong hydrodynamic interactions in two-dimensional Stokes flow, the concept of hydrodynamic diffusivity in the limit of infinite dilution is ill-defined in the absence of fluid inertia. Dynamical simulations of doubly periodic monodisperse suspensions with up to 50 capsules distributed in each periodic cell at areal fractions of 0.25 and 0.40 provide information on the effective rheological properties of the suspension and on the nature of the statistical propel-ties of the particle motion. The character of the flow is found to be intermediate between that of liquid drops and rigid particles, and this is attributed to the membrane deformability and to the ability of the interfaces to perform tank-treading motion. The results are compared with rheological measurements of blood flow with good agreement.