Fully-resolved Lattice Boltzmann Simulation Of Three Dimensional Particle Settling

The particle-fluid system is widely used in the environmental engineering?biology and industrial applications. The movement of suspended particles is a hot and difficult problem in the field of multiphase flow, especially for the law of particle swarm. In this paper, the lattice Boltzmann method(LB) + external boundary force method(EBF)+ MPI parallel program are used to simulate the motion of the suspended particles. Particle motion is described by the Newton equation of motion, the collision between the particles are solved by the particle collision model proposed by Glowinski et al in 2001.This paper mainly studies three dimensional single, double particle and particle swarm movement regularity and its mechanism?Firstly, effects of different initial position of the particle in the wall boundary condition and different boundary conditions are simulated. In wall boundary condition, the single particle in different initial position has a weak effect on the velocity in the beginning, but does not affect the final sedimentation velocity. Initial position of the particle is not in the center position will produce the rotary motion of particle. The settling velocity in free boundary condition is the fastest, followed by the periodic boundary condition and the wall boundary condition.Secondly, this paper analyzes the movement of particles of the same sizes and different sizes in detail. In the study of particles of different sizes, we find a number of critical values when the small particle above the big particle, including the ratio of diameter?initial spacing of the particles and the density ratio of the particles. The particle motion is divided into two areas by the critical values, DKT phenomenon just occurs in one area. The key of occurrence of the DKT phenomenon is that the small particle can catch up with the big one with the particle's wake attraction under different parameters of the particles in a certain time.Finally, this paper has studied on the motion of particle swarm, including the influence of different initial position and the simulation of 144 particles and 1152 particles. We have a certain understanding to the whole movement of particles by analyzing the speed and position of the particles; we also analyze the interaction between the particle and the fluid. In addition, this paper has studied the influence of Ga and the volume fraction.The oscillation of vertical settlement average Re is weak when Ga is small; while the oscillation of vertical settlement average Re(i.e. the average speed of the particles) is strong when Ga is big, the interaction between particle and fluid is strong, the interaction between particle and particle is also strong, and the flow field of vortex has a big value. The surface of the vortex is smooth when Ga is small, then the surface of the vortex become wrinkling, broken with the increase of Ga.