Investigations of two-phase flow in porous media using a total velocity-based numerical model.

摘要

A total velocity-based, two-phase flow numerical model is presented to predict the movement of any two immiscible fluids in shallow, subsurface environments. The model simulates one-dimensional flow in homogeneous or two-layer soil systems and accommodates a variety of initial and boundary conditions. The model is based on a partial differential equation for volume conservation of water (combined with Darcy's law) and an integral equation for total velocity. Total velocity is the sum of the wetting fluid velocity (i.e. water) and nonwetting fluid velocity (i.e. air or an immiscible organic fluid) for two fluids present in a porous medium.; Simulations conducted with the model included infiltration without ponding in a fine over coarse soil and in a coarse over fine soil; ponded infiltration in a fine over coarse soil without air compression; flow of water and an immiscible organic fluid in a homogeneous, vertical soil column; and flow of water and an immiscible organic fluid in a two-layer porous medium. Water content profiles were plotted and mass balance was checked after each simulation. Model output for the water and air flow cases was compared to SWIM, a one-phase flow numerical model. The flow of water and an immiscible organic fluid was verified for homogeneous soils against exact integral solutions developed by others for horizontal, two-phase flow.; The water-air simulations for layered soils without ponding indicated that the water content profiles generated by the model were essentially identical to those generated by the one-phase flow SWIM model. However, the two-phase flow model provides information about the air phase that might be of value if the bulk air phase contains environmental contaminants. The two-phase flow model showed that the presence of a second layer can influence the direction of air flow during infiltration. For cases with ponding, the model showed that the presence of layers influences the time to ponding. Execution times for the two-layer, water-air system simulations were long, and convergence problems were encountered in several cases. The water-organic fluid system simulations were in agreement with physical expectations.