A CFD-DEM-IBM Method for Cartesian Grid Simulation of Gas-Solid Flow in Complex Geometries

The use of CFD-DEM method to accurately simulate gas-solid flows in complex geometries is challenging, mainly due to the complexity related to the use of unstructured computational grids. To this end, the gas-solid flows in complex geometries were simulated using Cartesian grids in present study, where the interactions between gas phase and complex geometries were firstly modelled using the immersed boundary method (IBM) implemented in OpenFOAM, it was found that the computational efficiency is quite low. To improve the efficiency of the CFD-DEM-IBM solver, a new IBM method was then proposed by removing the neighboring immersed boundary cells from the interpolated extended stencil in the reconstruction of the velocity field near the wall, and proposing a new zero-gradient boundary condition to replace the original Neumann boundary condition for reconstructing the pressure field.

Single-phase flow past a stationary cylinder, single-phase pipe flow, gas-solid flow in a cylindrical fluidized bed and fluidized bed with immersed tubes were simulated with four different IBM imposition methods to assess the accuracy and efficiency of CFD-DEM-IBM solver. It was shown that the results of CFD-DEM-IBM simulations, which are more accurate than those of using unstructured grids, agree well with the reported experimental, analytical and/or numerical results available in literature, and the computational efficiency of newly proposed CFD-DEM-IBM solver is one or two order of magnitudes faster than that of the original IBM in OpenFOAM.