Direct numerical simulation of freely falling particles by hybrid immersed boundary – Lattice Boltzmann – discrete element method
In this study, a coupling rule based on Lattice Boltzmann Method (LBM), Immersed Boundary Method (IBM), and Discrete Element Method (DEM) was developed to simulate settling of particles in Newtonian liquid. The direct forcing IB-LBM, which was enhanced by the split-forcing technique, was utilized to account for fluid/solid interactions. Dynamic behavior of particles during collisions was evaluated by DEM, in which contact forces were computed based on overlap distances and relative velocity between two particles. The lubrication force was also included in equation of motions that allowed the coupled IB-LB-DEM to accurately account for the fluid film before collision. The hybrid model was verified by examining the freely falling of single and tandem circular particles in a vertical box. The particle-particle collision was included in the model and particular attention was given to the examination of the effects of collision parameters including restitution and friction coefficients on the particle sedimentation behavior. The transverse and longitudinal positions and velocities of two falling particles are compared for a wide range of physical parameters. Finally, free falling of 28 particles for two different friction coefficients were simulated to show capability of the new model for analyzing particulate flows.
Keywords: Collision model, Discrete element method, drafting, immersed boundary-Lattice Boltzmann method, kissing, tumbling