COMPARISION OF NUMERICAL MODELS FOR ADVECTION DISPERSION EQUATION

Abstract

In recent years there has been a tremendous increase in the contamination of groundwater due to rapid industrial growth and use of fertilizers and pesticides in agriculture. As this contaminated water passes through the soil and may produce hazardous chemicals, which are risk to public health. For this purpose it is necessary to understand the movement of contaminated groundwater for taking up proper remedial measures. Numerical models are very important tools for studying the movement of contaminants in groundwater. The present study is concerned with comparison of the performance of finite volume method and polynomial interpolation scheme for nonreactive solute pulse. In the present study an operator-split approach is used for solving the contaminant transport equation, which uses an Eulerian framework with finite volume and also polynomial interpolation for advection transport and fully central difference method for dispersive transport. This hybrid formulation helps in accurately simulating both high advective and dispersive transport cases with less restriction on grid size and time step. The model is tested using various analytical solutions for nonreactive cases while analyzing various advection dispersion dominated situations. Different initial and boundary conditions are used which mimic the laboratory and field situations. These laboratory and field situations are analyzed in order to study the numerical dispersions, peak clipping and grid orientation. The model is tested for various Peclet and Courant numbers by using finite volume and polynomial interpolation method. It is observed that the finite volume model gives better results and no oscillations were observed. But incase of polynomial interpolation method oscillations were observed at corners and peaks. The role of suitable flux limiter such as Minmod limiter, Superbee limiter and Van Albada limiter are used in the finite volume method for tracking sharp concentration iii profile and it is observed that the Superbee limiter is better for tracking sharp concentration fronts. The nonreactive and reactive solute pulses are compared using finite volume method for advection and fully central difference method for dispersive transport, it is observed that the movement of concentration of the reactive solute is less as compared with nonreactive solute pulse. The reactive model is tested for various distribution coefficients and it is observed that as distribution coefficient increases the movement of concentration decreases.