  Discrete particle simulation, a combined approach of computational fluid
dynamics and discrete methods such as DEM (Discrete Element Method), DSMC
(Direct Simulation Monte Carlo), SPH (Smoothed Particle Hydrodynamics), PIC
(Particle-In-Cell), etc., is becoming a practical tool for exploring lab-scale
gas-solid systems owing to the fast development of parallel computation.
However, gas-solid coupling and the corresponding fluid flow solver remain
immature. In this work, we propose a modified lattice Boltzmann approach to
consider the effect of both the local solid volume fraction and the local
relative velocity between particles and fluid, which is different from the
traditional volume-averaged Navier-Stokes equations. A time-driven hard sphere
algorithm is combined to simulate the motion of individual particles, in which
particles interact with each other via hard-sphere collisions, the collision
detection and motion of particles are performed at constant time intervals. The
EMMS (energy minimization multi-scale) drag is coupled with the lattice
Boltzmann based discrete particle simulation to improve the accuracy. Two
typical fluidization processes, namely, a single bubble injection at incipient
fluidization and particle clustering in a fast fluidized bed riser, are
simulated with this approach, with the results showing a good agreement with
published correlations and experimental data. The capability of the approach to
capture more detailed and intrinsic characteristics of particle-fluid systems
is demonstrated. The method can also be used straightforward with other solid
phase solvers.
