Numerical Solution To Subsurface Transport Of Non-Aqueous Liquid Containment

Groundwater has always been related to people's living health and social and economic situation;land is an important material basis for social production and human life.With the continuous development of social economy and the endlessly expansion of industrial scale,the dependence on energy of human has gradually deepened.However,in recent years,the phenomenon of underground environmental pollution is emerging in endlessly.The transport of non-aqueous phase liquids(NAPLs)contaminants,as multiphase seepage phenomenon,is becoming increasingly prominent and complex in the purification of groundwater.In this paper,a mathematical model has been established to describe the transport behavior of Non-Aqueous Fluids in saturated and vadose zone in soils,according to the characteristics of multiphase flow of water,gas and NAPLs in porous media and drawing experience on the mathematical model of groundwater seepage.In the analysis of porous media system that composed of water,gas and NAPLs,the influences of the following factors were considered synthetically: 1)the interfacial tension characteristics of each phase fluid under complex environmental conditions in soil;2)the interaction mechanism between various fluid substances;3)the relationship between the wettability of fluid and its adsorption form in soil pores.The finite element method based on Galerkin discretization and the corresponding implicit iterative algorithm have been developed.By simulating the multiphase flow process in the soil,the spatial-temporal distribution characteristics and pollution range of NAPLs pollutants can be obtained,which provides a scientific basis for quantitative prediction of pollutant purification and treatment design.This paper has mainly studied the following two contents:(1)According to the mathematical model of groundwater seepage analysis and the international advanced three-phase capillary-saturation model,and comprehensively using the numerical methods of finite element and finite difference,the theory of strong nonlinearity flow transfer analysis of immiscible contaminants that dominated by interface tension in saturated and vadose zone in groundwater in the soil was derived.And the numerical discretizing solution was established.Galerkin discretized finite element method is used in the domain space of mathematical model solution,and the time evolution is discretized by finite difference method.This model has taken into account the existence of water,NAPLs and air in the research system,and it can be closer to the actual behavior of pollutant leakage and migration.(2)On this basis,the three-dimensional finite element method of two-phase flow in porous media and its corresponding Fortran source code program were developed.The large sparse matrix after finite element discretization is stored in the form of one-dimensional variable bandwidth to improve the efficiencies of the program.In this paper,the source code is applied to the transport problem of underground immiscible pollutants,and the transport and diffusion behavior of pollutants in groundwater after migrating to groundwater level is simulated.Two typical examples are given to verify the correctness of the program and algorithm.In particular,the two phase flow code of FLAC2 D is used to simulate the same calculation example,and the correctness of the program is further verified by comparison.