(10)
where μf is the fluid viscosity.
The Kozeny–Carman relation (Kozeny et al., 1927; Carman 1939) was used to estimate the permeability. Two-way coupling was accomplished by updating the permeability coefficient information for each fluid element and updating the fluid velocity field of each discrete element. The permeability of each fluid element was calculated from the porosity of the PFC3D model, and the calculation is given by Eq. (11),