COMPUTER SIMULATION OF PARTICLE AGGREGATES DURING SEDIMENTATION
COMPUTER SIMULATION OF PARTICLE AGGREGATES DURING SEDIMENTATION
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沉降过程中颗粒聚集体的计算机模拟
DOI：
10.1016/j.cma.2007.05.022
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发表时间：
2007
影响因子：
7.2
通讯作者：
F. R. Cunha
中科院分区：
文献类型：
--
作者：
G. Abade;F. R. Cunha
本文研究了低雷诺数重力沉降过程中微粒速度波动的数值研究。模拟是通过直接计算大量球形颗粒之间的水动力相互作用来完成的。我们将注意力集中在单分散和稍微多分散的球形聚集体上，这些聚集体由半径约为均值的高斯分布的无惯性粒子组成。在消失的粒子斯托克斯数下，分散的粒子发生随机位移，这是由流体速度的随机环境场引起的，而不是由直接的固体碰撞引起的。随着沉降的进行，一个单分散的斑点作为一个有凝聚力的实体持续存在，斑点边界的零星向外粒子交叉。对于颗粒从聚集体中泄漏的速率，提出了一个尺度论点。当引入足够高的多分散度时，根据固体体积分数的不同，聚集体的行为将不同于单分散的团块。观察到的颗粒的波动运动，如果将其视为一个有效的连续体，则可以定义与斑点的颗粒相相关的颗粒压力。对于多分散的斑点，速度波动引起的颗粒扩散趋势清楚地表明颗粒压力对悬浮流动中固体体积分数不均匀形成的抵抗作用。
This work concerns with a numerical investigation of particle velocity fluctuations in a blob undergoing gravity induced sedimentation at low Reynolds number. The simulations were performed by direct computation of the hydrodynamic interactions between a large collection of spherical particles. We focus our attention on both monodisperse and slightly polydisperse spherical aggregates comprised of inertialess particles whose radii have a Gaussian distribution about the mean. At vanishing particle Stokes number the dispersed particles undergo stochastic displacements arising from the random ambient field of the fluid velocity and not from direct solid-body collisions. As the sedimentation proceeds, a monodisperse blob persists as a cohesive entity with sporadic outward particle crossings of the blob boundary. A scaling argument for the rate at which the particles leak away from the aggregate was developed. When a sufficiently high degree of polydispersity is introduced the aggregate will behave differently from a monodisperse blob depending on the solid volume fraction. The observed fluctuating motion of the particles leads to the definition of a particle pressure associated with the particulate phase of the blob if it is regarded as an effective continuum. For polydisperse blobs, the tendency to a particle spreading induced by velocity fluctuations makes clear the effect of the particle pressure on resisting the formation of solid volume fraction inhomogeneities in suspension flows.