Orbital drift of capsules and red blood cells in shear flow
Orbital drift of capsules and red blood cells in shear flow
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DOI：
10.1063/1.4820472
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发表时间：
2013-09-01
影响因子：
4.6
通讯作者：
Bagchi, Prosenjit
中科院分区：
文献类型：
--
作者：
Cordasco, Daniel;Bagchi, Prosenjit
许多数值研究都考虑了在胶囊和红细胞的旋转轴保持在剪切面上的条件下，胶囊和红细胞在剪切流中的动力学。相比之下，几项实验研究表明，在一定的控制参数范围内，红细胞的旋转轴可能会偏离剪切面。本文对不同初始未变形形状，即长圆形、扁圆形和双凹形的胶囊在简单剪切流动中的取向动力学进行了三维数值模拟。观察到，与Stokes流中的刚性椭球不同，胶囊的旋转轴在进动运动时朝向涡量轴，或在皮划艇运动时朝向剪切面。观察到比动力学取决于初始形状、毛细管数和内外流体粘度之比。在粘度比的生理值附近，双凹形状执行轮子一样的滚动运动。如果粘度比降低到生理范围以下，则随着毛细管数的增加，观察到向皮划艇动力学的转变。研究发现，发生从滚转到皮划艇转变的临界剪应力与粘度比有关。(C)2013 AIP出版有限责任公司。
Many numerical studies have considered the dynamics of capsules and red blood cells in shear flow under the condition that the axis of revolution of such bodies remained aligned in the shear plane. In contrast, several experimental studies have shown that the axis of revolution of red blood cells could drift away from the shear plane in a certain range of controlling parameters. In this article, we present three-dimensional numerical simulations on the orientation dynamics of capsules in simple shear flow with different initial undeformed shapes, namely, prolate, oblate, and biconcave disk. It is observed that unlike rigid ellipsoids in Stokes flow, capsules reorient their axis of revolution either towards the vorticity axis while undergoing a precessing motion or towards the shear plane while undergoing a kayaking-type motion. The specific dynamics are observed to depend on initial shape, capillary number, and the ratio of the internal to external fluid viscosity. Near the physiological values of the viscosity ratio, the biconcave shape performs a rolling motion like a wheel. If the viscosity ratio is reduced below the physiological range, a transition to the kayaking dynamics is observed with increasing capillary number. The critical shear stress at which the rolling-to-kayaking transition occurs is found to be dependent on the viscosity ratio. (C) 2013 AIP Publishing LLC.