Computation of the Beavers-Joseph slip coefficient for coupled Stokes/Darcy problems.

Physically consistent coupling conditions at the fluid-porous interface with correctly determined effective parameters are necessary for accurate mathematical modeling of various applications described by coupled free-flow and porous-medium problems. To model single-fluid-phase flows at low Reynolds numbers in such coupled systems, the Stokes/Darcy equations are typically used together with the conservation of mass across the fluid-porous interface, the balance of normal forces and the Beavers-Joseph condition on the tangential component of velocity. In the latter condition, the value of the Beavers-Joseph slip coefficient is uncertain, however, it is routinely set equal to one that is not correct for many applications. In this paper, three flow problems (pressure-driven flow, lid-driven cavity over porous bed, general filtration problem) with different pore geometries are studied. We determine the optimal value of the Beavers-Joseph parameter for unidirectional flows minimizing the error between the pore-scale resolved and macroscale simulation results. We demonstrate that the Beavers-Joseph slip coefficient is not constant along the fluid-porous interface for arbitrary flow directions, thus, the Beavers-Joseph condition is not applicable in this case.