三维颗粒（群）沉降的格子Boltzmann全解析数值模拟

发布时间：2018-05-22 16:42

本文选题：悬浮粒子流 + 格子Boltzmann　；参考：《华中科技大学》2015年硕士论文

【摘要】：颗粒-流体系统广泛存在于环境工程、生命科学以及工业应用等领域,其中对于悬浮颗粒运动规律,尤其是颗粒群的运动规律是多相流领域的一个热点难点问题。本文采用格子Boltzmann方法(LB)+附件边界应力方法(EBF)+MPI并行程序来模拟悬浮颗粒(群)的运动规律,颗粒的运动由牛顿运动方程进行描述,颗粒与颗粒颗粒之间的碰撞采用Glowinski等人2001年提出的碰撞模型进行处理。本文主要研究的是三维单、双颗粒以及颗粒群的运动规律及背后存在的机理。首先,本文模拟了壁面边界条件下不同初始位置对颗粒运动的影响以及不同周期边界条件对颗粒运动的影响。在壁面边界条件下,单颗粒位于不同初始位置时虽然起初会对速度有微弱影响,但并不影响其最终沉降速度;初始位置处于非中心位置时,颗粒会产生旋转运动。对于不同边界条件下单颗粒的运动进行研究,我们发现单颗粒在自由边界条件下沉降的最快,其次是周期边界,最后是壁面边界。其次,本文详细分析了等粒径颗粒和非等粒径颗粒的运动规律,在非等粒径颗粒的研究中我们发现小颗粒在上时出现了多个临界值,包括粒径比、初始间距、密度比,这些临界值将颗粒运动分成两个区域,一个是能发生DKT现象的区域,另一个则是不能发生DKT现象的区域,而能不能发生DKT现象的关键在于不同参数下颗粒尾涡的吸引能不能导致后面颗粒在一定时间间距内赶上前面颗粒。最后,本文对颗粒群运动进行了模拟研究,包括不同初始位置对颗粒群运动的影响以及100数量级和1000数量级颗粒群的模拟,通过对速度及其统计量分析、位置及其统计量分析、颗粒流体相互作用分析使得我们对于颗粒群整体运动规律和机理有了一定的认识。另外本文针对颗粒群系统的Ga和体积分数进行了研究,Ga较小时颗粒竖直沉降平均Re的震荡微弱,Ga较大时,颗粒竖直沉降平均Re的震荡强烈,颗粒-流体及颗粒-颗粒间的相互作用明显,流场涡量值较大,涡结构由平滑到皱褶再到破碎、脱落。
[Abstract]:Particle fluid systems are widely used in environmental engineering, life sciences and industrial applications. Among them, the motion law of suspended particles, especially the motion of particle groups, is a hot and difficult problem in the field of multiphase flow. In this paper, the lattice Boltzmann method is used to simulate the motion of suspended particles (groups) by using the adnexal boundary stress method (EBF) MPI. The motion of particles is described by Newtonian equation of motion. The collision between particles is treated by the collision model proposed by Glowinski et al in 2001. In this paper, the motion and mechanism of three dimensional single, double particles and particle groups are studied. Firstly, the effects of different initial positions on particle motion and the effects of different periodic boundary conditions on particle motion under the wall boundary condition are simulated. Under the condition of wall boundary, single particle at different initial position will have weak influence on velocity at first, but it will not affect the final settlement velocity, and when the initial position is in non-central position, the particle will produce rotational motion. For the study of the movement of the ordered particles under different boundary conditions, we find that the settlement of single particles is the fastest under the free boundary condition, followed by the periodic boundary, and finally the wall boundary. Secondly, in this paper, we analyze the movement law of equal and non-equal size particles in detail. In the study of non-equal particle size, we find that there are several critical values when small particles are up, including particle size ratio, initial spacing, density ratio. These critical values divide the motion of particles into two regions, one where the DKT phenomenon can occur, and the other where the DKT phenomenon cannot occur. The key to the occurrence of DKT phenomenon lies in the attraction energy of particle wake under different parameters, whether the latter particles catch up with the front particles within a certain time interval. Finally, the motion of particle group is simulated, including the influence of different initial position on particle group motion, and the simulation of 100th and 1000 order of magnitude particle group. Through the analysis of velocity and its statistics, the position and its statistics are analyzed. The analysis of particle-fluid interaction gives us a certain understanding of the law and mechanism of particle group motion. In addition, for the Ga and volume fraction of the particle group system, it is studied that when the oscillation of the average re of the vertical sedimentation of particles is weak and Ga is large, the oscillation of the average re of the vertical sedimentation of the particles is strong. The interaction between particle and fluid and between particle and particle is obvious, the vorticity of flow field is larger, and the vortex structure changes from smoothness to wrinkle to breakage and shedding.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O347.7;O241

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