Lattice Boltzmann simulations of sedimentation of a single fiber in a weak vertical shear flow
Lattice Boltzmann simulations of sedimentation of a single fiber in a weak vertical shear flow
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DOI：
10.1063/1.4821775
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发表时间：
2013-09
影响因子：
4.6
通讯作者：
D. Qi;G. He;Ying-ming Liu
中科院分区：
文献类型：
--
作者：
D. Qi;G. He;Ying-ming Liu
悬浮液的不稳定性直接关系到一个粒子相对于其邻近的粒子悬浮液的横流迁移问题。利用晶格玻尔兹曼模拟研究了单个非球形颗粒（纤维）在有界弱剪切流中沉降的横流或横向迁移，该流具有由纤维数密度扰动产生的垂直流线。模拟结果表明，在一定剪切速率下，根据沉降雷诺数R-sd和颗粒展弦比kappa，横向运移可分为三个阶段。在较低的沉降雷诺数R-sd下，悬浮液在第一阶段变得更加稳定。当R-sd增加并超过临界沉降雷诺数R-sd1时，纤维悬浮液在第二阶段变得不稳定。在阶段3，当R-sd足够大时，惯性主导弱剪切流，对稳定性影响不大。最近，Shin、Koch和Subramanian在《有限雷诺数沉淀纤维的稀释悬浮物的结构和动力学》中提出了一种由惯性光纤取向漂移和剪切诱导的交叉流线漂移引起的不稳定机制。流体21,123304(2009)]，经检查并确认。
Instability of a suspension is directly related to the problem of the cross-stream migration of a particle relative to its neighboring particle suspension. Such cross-stream or lateral migration of a single non-spherical particle (fiber) settling in a bounded weak shear flow with vertical streamlines produced by a perturbation to the fiber number density is studied using lattice Boltzmann simulations. The present simulation results demonstrate that at a given shear rate, the lateral migration can be divided into three phases depending on settling Reynolds number R-sd and particle aspect ratio kappa. At a low settling Reynolds number R-sd, the suspension becomes more stable in phase 1. As R-sd increases and excesses a critical settling Reynolds number R-sd1, the fiber suspension becomes unstable in phase 2. In phase 3, at an enough large R-sd, the inertia dominates the weak shear flow and it may have little effect on stability. A mechanism of the instability induced by an inertial fiber orientation drift and a shear induced cross-streamline drift, recently proposed by Shin, Koch, and Subramanian ["Structure and dynamics of dilute suspensions of finite reynolds number settling fibers," Phys. Fluids 21, 123304 (2009)], is examined and confirmed.