A finite volume model for the hydrodynamics of combined free and porous flow in sub-surface regions

In this paper, a finite volume model for the 3-D analysis of sub-surface water flow is described. The model is applied to simulate groundwater hydrodynamics in domains representing combined free flow and porous sections. The free flow section is isotropic, while the porous section is assumed to be a saturated and anisotropic medium with a constant porosity. The Navier-Stokes equations are used to simulate the free flow regime, while the porous flow is modelled by the Darcy equation. The governing equations of motion for each sub-domain are linked through the imposition of suitable matching conditions at the free/porous flow interface. At the exit from the domain, 'no boundary condition' is imposed to avoid forcing of any artificial condition on the flow system. This is guided by previously published work that recommends this approach for obtaining realistic simulations for complex flow systems. Results presented in this paper show that depending on pressure distribution, underground flow circulation inside the porous domain may occur. It is also shown that the direction of the porous flow may reverse at the interface, with the flow front reversal and the circulation centre moving away from their initial positions with time. (C) 2002 Elsevier Science Ltd. All rights reserved.