Fully-resolved Lattice Boltzmann Simulation Of The Particle Suspension Flow

The particle-fluid system has widely varying applications in the fields of nature,industrial engineering and biology. The particle suspensions, particle-fluid interactions andparticle-particle interactions are attracting considerable attentions. The particle suspensionflows are investigated employing the fully-resolved Lattice-Boltzmann method (LBM) withdiscrete external boundary force (EBF) in this thesis. The flow around the particle isresolved by LBM. The no-slip boundary condition at the fluid-particle interface is enforceddirectly by adding the external boundary force to the fluid domain and the particle-fluidinteraction force is directly obtained. Also particle-particle collisions are considered and theparticle motions are captured by the Newtonian dynamic equations.The sedimentations of the suspended particles are simulated in this work, and theparticle motions are revealed by presenting the particle position plots, spacing plots,particle translation velocities, and particle angular velositites. Moreover, the fluidmicrostructure like the vorticity contour, pressure contour and velocity contour arepresented to reveal the particle-fluid and particle-particle interactions.Firstly, the motions and dynamics of two freely settling spherical particles withdifferent initial configurations are investigated. Three different regimes are found to controlthe two particles settling system: repulsion, attraction and transition regime. Each regimedepends on the initial separation distance and the relative angle of the two particles.However, the relative angle plays the main dominant role, while the initial separationdistance only plays an important role in the transition regime. For the same initialseparation distance, the initial relative angle plays an important role: large relative anglemore likely leads to the attractions including DKT motion, while small initial relative anglemore likely leads to repulsion process during the settling. For the same initial relative angle,the initial separation distance influnce the appearance frequency of the transition regime.Moreover, the key parameter to determine the particle motions and dynamics is given inthis work.Moreover, the motions and interactions of many identical partiles (3to100) settling in the long vertical channel are investigated. The settling processes for the many particles areidentified into three stages: Acceleration, Deceleration and Oscillation. The underlyingdynamics for each stage are detailed anlysesed. The DKT montions, repulsion processes,particle aggregation and V-front structures are revealed and we find that the particle wakesplay an important role on the particle motions. Moreover, the particle suspension processesunder periodic boundary condition are simulated with9and27particles.Finally, the sedimentation processes of particles with different diameters areinvestigated. Two different particles setlling one behind the other and side by side aredetailed anlysesed. When the small particle is initially located on the upper side of the largeparticle, the DKT motion may not happen if the large-small particle dimater ratio is biggerthan a certain critical value. When the two different particles are initially located side byside, the repulsion process will not show. Further, the sedimentation of many particles withtwo different diameters settling in a long vertical channel is simulated to find the DKTmotions and V-front structure.