(2)
where u is the particle velocity, m is the particle mass, ffluid is the total force applied by the fluid on the particle, fmesh is the sum of additional forces (externally applied forces and contact forces) acting on the particle, g is the acceleration due to gravity, ω is the particle angular velocity, I is the moment of inertia, and M is the moment acting on the particle.

2.2 Governing Equations of the Fluid Phase

In the CFD–DEM method, the Darcy fluid model has been proven to be an effective and efficient method for predicting fluid behaviour using an appropriate permeability (Goodarzi et al., 2014; Cui et al., 2016; Tang et al., 2017). The Darcy fluid model was adopted for the fluid flow simulation in this study. The governing equations of the transient fluid flow through a saturated porous media based on the Darcy model and the fluid phase are assumed to be incompressible.