A numerical simulation study on the spontaneous imbibition and hydro-thermal coupling in soil using the lattice Boltzmann method

Abstract

This study presents a numerical simulation of underground water spontaneous upward imbibition at high density ratios using the improved lattice Boltzmann method coupled with the P-R equation of state. Porous media was created using the Quartet Structure Generation Set (QSGS) method. The research delved into the impact of factors such as porosity, soil particle size, capillary force, gravity and temperature on spontaneous imbibition. The results indicated that the permeability coefficient of water spontaneous imbibition rises with higher porosity or larger particles. The influence of gravity on spontaneous imbibition became more significant with increased porosity. Three levels of porosity, namely 0.80, 0.65, and 0.50, were simulated to determine the prevailing force between the thermal-driven force and the gravitational hindrance. The variation of groundwater spontaneous imbibition permeability coefficient under the influence of gravity at different temperature gradients was simulated, as was the change in the permeability coefficient without the influence of gravity. The results revealed that for temperature differences above 4 K, gravity had minimal impact with temperature being the main influential factor. For example, for simulation with temperature difference of 10 K, the permeability coefficient differences were 0.006, 0.015, and 0.014 for the three different porosity levels, respectively. When the temperature difference was below 4 K, the disparity in the permeability coefficient increased significantly compared to zero-gravity conditions. Under these conditions, the influence of gravity was greater. For example, for simulation with temperature difference of 2 K or greater, the permeability coefficient differences were 0.306, 0.300, and 0.108 for the corresponding porosity values respectively.