An improved model based on lattice Boltzmann method for the simulation of water and salt migration in unsaturated soils

It is of significant scientific and engineering importance to investigate the fluid flow and mass transfer processes occurring in porous media. In this study, the lattice Boltzmann method (LBM)-based multiphase flow mass transport model is improved using the pseudo-potential model theory and the colour gradient model theory. The improved model is verified in terms of its ability to simulate coupled multiphase flow and mass transport processes and the optimisation of computational efficiency. The model is then employed to study the migration of water and salt in soil, and the results demonstrate that the transport of salt species is primarily influenced by the transport of water. Additionally, under isothermal conditions, there are minor fluctuations in the constant water content in the soil, which can be attributed to local evaporation and condensation processes driven by moisture gradients. Finally, the mechanism of local evaporation leading to local solute concentration was also subjected to investigation.