(445e) Effect of Particle-Fluid Density Ratio on the Stability of Sedimentation or Fluidization of Spherical Particles Using Lattice-Boltzmann Method

Stability of particle-fluid system is studied by employing the Lattice-Boltzmann method. We simulated the sedimentation or fluidization of particles in periodic domains. The Archimedes numbers of the spheres are 71 and 1432, which correspond to particle Reynolds numbers of 3 and 30, respectively, based on the terminal velocities. Solid fractions in the suspensions are 10%, 15%, 25%, 40%. The normal restitution coefficient between particles is selected to be 0.9 and 1.0 to represent cases with and without dissipative collisions. The fluid-particle density ratio was varied from 2 to 1000 to explore the effect of particle-fluid density ratio on the dynamics and stability of the suspension. The unstable transition due to continuously varying particle-fluid density ratio is investigated and quantitative measures of transition are established. As the solid-fluid density ratio is increased, at first transient occurrence of clusters is observed, followed by formation of stable traveling waves. The effect of solid fraction and normal restitution on the point of stability transition are studied. Present investigations are supported by NSFC through Grant No. 51106039 and NSF through Grant No. CBET 1236157 and 1236490.