(207g) Stability Boundaries for Sedimentation or Fluidization System of Particle-Fluid Flows

The onset of instability in a fluid-particle system is of great importance due to the fact that instability can give rise to clustering and result in a transformation of fluid-particle drag force. In this work, the effect of particle-fluid density ratio on the stability of sedimentation or fluidization of spherical particles is studied. Stability boundaries for sedimentation or fluidization system of fluid-particle flows are drawn based on simulation results in periodic domains. The Archimedes numbers of the spherical particles are selected to be 71 and 1432, corresponding to particle terminal Reynolds numbers of 3 and 30, respectively, based on the terminal velocities. The particle-fluid density ratio was increased from 2 to 1000, and solid fractions in the systems are 0.1, 0.15, 0.25 and 0.4. The stable-unstable transition due to continuously increasing particle-fluid density ratio is investigated. By using quantitative measures of transition established in our previous work, we show that Reynolds number and solid fractions exhibit the greatest effects on the onset of instability for fluid-particle system. The effect of dissipative collisions of particles are taken into account by selecting the normal restitution coefficient between particles to be 0.9. However, this did not generate very significant impact on the stability boundaries.

Present investigations are supported by NSFC through Grant No. 51106039 and NSF through Grant No. CBET 1236490.