Study On The Gravity-Driven Motion And Interaction Of Particles

Particle two-phase flow has always been a classic problem in fluid mechanics due to its widespread existence in nature and extensive use in industrial production.In this paper,the settling and rising of circular particles,the settling of spheres,and the rising of self-propelled particles are studied by using the lattice Boltzmann method combined with an improved bounce-back scheme.The results are as follows:(1)Numerical calculations are carried out on the settling of circle particles,the effects of density ratio and diameter ratio between particles are mainly considered.Maximum and minimum value of density ratio between particles have a good power-law relationship with the diameter ratio within the selected Reynolds number range(10 ≤Re≤50).And when the diameter ratio is small,the effect of Re on the maximum and minimum values of density ratio between particles is significant.In addition,a unique horizontal oscillatory motion(HOM)pattern was revealed.(2)For the rising of circle particles,the effects of Reynolds number(5≤Re≤10)and density difference between the particles on the motion and interactions of particles were studied.Numerical results include streamlines,particle motion trajectories and phase diagrams.The transition of particle motion mode occurs ’when the value of density difference increase,and each transition between the modes of particles motion is accompanied by a sudden increase in the rising velocity of particles.In addition,the critical value of mode transition is not a constant which is found to increase with the Reynolds number.(3)A three-dimensional lattice Boltzmann method was employed to simulate the settling of two spheres in a square tube,which were released from rest at an initial plane.The effects of the initial arrangements of spheres and the Reynolds number on the terminal settling plane where the spheres are sedimenting steadily were studied.It has been found that the spheres tend to deflect more towards the diagonal or anti-diagonal planes at intermediate Reynolds munbers.In addition,the angle between the terminal settling plane and the center-line plane shows a trend of first decreasing and then increasing with the Reynolds number for all cases studied.(4)The widely-used squirmer(self-propelled)model was incorporated into the lattice Boltzmann method with an improved bounce-back scheme.Then the motion and interactions of squirmers in the vertical channel were numerically investigated.The effects of the self-propelled intensity as well as the self-rotation magnitude were revealed.