  A systematic study is carried out on a fully resolved fluid-particle model
which couples the Lattice Boltzmann Method (LBM) and the Discrete Element
Method (DEM) using an immersed moving boundary technique. Similar algorithms
have been reported in the past decade, however, the roles of major model
parameters are yet to be fully understood. To examine various numerical errors,
a series of benchmark cases with a wide range of Reynolds number are performed,
starting from a single stationary particle to multiple moving particles. It is
found that for flow with low and intermediate Reynolds numbers, 20 fluid cells
per one particle diameter are necessary to achieve sufficient accuracy (within
5%). For a flow with high Reynolds number, a turbulence model shall be
incorporated so that the effects of unresolved small eddies can be captured in
an accurate and efficient manner. Besides, the LBM-DEM results are also
sensitive to the relaxation time, especially when the spatial resolution is
inadequate. A large relaxation time can introduce additional diffusion of fluid
momentum into the fluid-particle system, leading to weakened hydrodynamic
interactions. By choosing a small relaxation time greater than the lower limit
0.5, a small fluid compressibility error and a strong coupling between fluids
and particles can be achieved, at the cost of computational effort. The test
cases also demonstrate the capability of LBM-DEM to describe the rheology of
particle suspensions by capturing the pore-scale hydrodynamic interactions.
Finally, a guideline for quickly establishing a high-quality LBM-DEM model is
provided.
