Tank-treading and tumbling frequencies of capsules and red blood cells.
Tank-treading and tumbling frequencies of capsules and red blood cells.
复制标题
胶囊和红细胞的坦克踩踏和翻滚频率。
DOI：
10.1103/physreve.83.046305
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
P. Bagchi
中科院分区：
文献类型：
--
作者：
Alireza Z. K. Yazdani;R. Kalluri;P. Bagchi
这项研究在一定程度上是由于文献中存在的关于红细胞踩罐频率与剪切率和悬浮介质粘度的关系的差异。在这里，我们考虑了可变形胶囊的三维数值模拟，这些胶囊最初是球形和扁圆形的，而双凹的盘状则代表了红细胞的静止形状。通过考虑粘度比(胶囊或细胞内部与悬浮液粘度之比)、剪切率和长径比(长径比)比以前的实验所考虑的更宽的范围，我们发现了几个以前没有报道过的坦克踩踏和翻滚频率的新特性。这些新的特征是大的形状变形和胶囊或细胞的形状和角振动之间的耦合的结果。对于球形和扁球形胶囊，坦克踩踏频率呈现出一个非单调的趋势，其特征是随着粘度比的增加，先是降低，然后是最小值，然后是增加。对于红细胞，我们发现了坦克踩踏频率的粘度依赖性的两个区域：指数区域和对数范围，在指数区域中，坦克踩踏频率随着粘度比的增加而以较慢的速度下降，在对数范围内，坦克踩踏频率以更快的速度下降。虽然这一趋势与不同的保形胶囊理论模型很好地吻合，但在以前的实验结果中并不明显。当考虑剪切率依赖关系时，红细胞和高度拉长的初始形状的胶囊的槽踏频率呈现非单调趋势，其特征是先增加，然后达到最大值，然后随着剪切速度的降低而急剧下降。坦克踩踏频率的这种异常行为被证明是由于胶囊或细胞的类似呼吸的动力学，其特征是反复出现和没有深坑状的凹陷，以及巨大的摆动。我们进一步观察到，随着粘度比的增加，翻滚频率呈现下降的趋势，这与保形胶囊的理论结果相反，这是由于胶囊在流动的伸展象限内的周期性变形和优先排列所致。
This study is motivated in part by the discrepancy that exists in the literature with regard to the dependence of the tank-treading frequency of red blood cells on the shear rate and suspending medium viscosity. Here we consider three-dimensional numerical simulations of deformable capsules of initially spherical and oblate spheroidal shapes and biconcave discoid representing the red blood cell resting shape. By considering a much broader range of the viscosity ratio (ratio of capsule or cell interior to suspending fluid viscosity), shear rate, and aspect ratio (ratio of minor to major axes) than that considered in the previous experiments, we find several new characteristics of the tank-treading and tumbling frequencies that have not been reported earlier. These new characteristics are the result of the large shape deformation and the coupling between shape and angular oscillations of the capsules or cells. For the spherical and oblate spheroidal capsules, the tank-treading frequency shows a nonmonotonic trend that is characterized by an initial decrease leading to a minimum followed by an increase with increasing viscosity ratio. For red blood cells, we find two regimes of the viscosity dependence of the tank-treading frequency: an exponential regime in which the tank-treading frequency decreases at a slower rate with increasing viscosity ratio, and a logarithmic range in which it decreases at a much faster rate. While this trend agrees well with different theoretical models of shape-preserving capsules, it was not evident in previous experimental results. When the shear rate dependence is considered, the tank-treading frequency of red blood cells and capsules of highly elongated initial shapes exhibits a nonmonotonic trend that is characterized by an initial increase leading to a maximum followed by a sharp decrease with decreasing shear rate. This anomalous behavior of the tank-treading frequency is shown to be due to a breathing-like dynamics of the capsule or cell that is characterized by a repeated emergence and absence of deep, crater-like dimples, and a large swinging motion. We further observe that the tumbling frequency exhibits a decreasing trend with increasing viscosity ratio that is in contrast to the theoretical result for the shape-preserving capsules and is due to the periodic deformation and preferential alignment of the capsules in the extensional quadrant of the flow.
影响因子：
8.6
作者：
Skotheim, J. M.;Secomb, T. W.
通讯作者：
Secomb, T. W.