Mass and Momentum Transfer at fluid-porous interfaces: Jump Boundary conditions for non-parallel Flows
Abstract
We derive boundary conditions for two-dimensional parallel and non-parallel flows at the interface
of a homogeneous and isotropic porous medium and an overlying fluid layer by solving a macroscopic
closure problem based on the asymptotic solution to the generalized transport equations (GTE) in the
interfacial region. We obtained jump boundary conditions at the effective sharp surface dividing the ho-
mogeneous fluid and porous layers for either the Darcy or the Darcy-Brinkman equations. We discuss
the choice of the location of the dividing surface and propose choices which reduce the distance with the
GTE solutions. We propose an ad-hoc expression of the permeability distribution within the interfacial
region which enables to preserve the invariance of the fluid-side averaged velocity profile with respect
to the size r0 of the averaging volume. Solutions to the GTE, equipped with the proposed permeability
distribution, compare favorably to the averaged solutions to the pore-scale simulations (PSS) when the
interfacial thickness ∆ is adjusted to r0 . Numerical tests for parallel and non-parallel flows using the ob-
tained jump boundary conditions or the generalized transport equations show excellent agreement with
the GTE solutions, with experiments and pore-scale simulations. The proposed model of mass and mo-
mentum transport is predictive, requiring solely information on the bulk porosity and permeability and
the location of the solid matrix of the porous medium. Our results suggest that the Brinkman corrections
may be avoided if the ratio a = ∆/δB of the thickness of the interfacial region to the Brinkman pene-
tration depth δB is large enough, as the Brinkman sub-layer is entirely contained within the interfacial
region in that case. Our results can be easily extended to deal with three-dimensional configurations and
anisotropic porous media.