Numerical simulation of transition layer at a fluid-porous interface

The study of flow phenomena at the sediment-water interface is very important in the field of environmental hydraulics. When a porous layer is overlaid by viscous fluid flow, a thin transition zone between the layers is formed, which is responsible for the interfacial momentum and mass transfer. This layer, also referred as Brinkman layer, is associated with the depth of penetration of the influence from the free-fluid region. This paper presents the preliminary results of numerical simulation of the flow in a rectangular geometry representing the region around the interface between a fluid and a porous media. The geometry reproduces that experimentally investigated by Goharzadeh et al. [2005]. The flow was described by the Navier-Stokes equations in the free region and the Brinkman equation in the porous region. Numerical simulations were carried out in laminar steady-state flow using Multiphysics 3.5a, a CFD code, in a range of Darcy number Da from 8.13×10-8 to 2.43×10-6 and of fluid-based Reynolds number Ref from 6 to 21. The thickness of the transition layer, defined as the height below the permeable interface up to which the velocity decreases to Darcy scale was measured from the simulated flow field. Numerical data were generally lower than the experimental data, but they were in agreement with the observed trends because the thickness of the transition layer increased with the increasing Da whereas it was not greatly altered by the increasing Ref.