The Free and Porous Media Flow, Darcy interface uses the Navier–Stokes equations to describe the flow in the free-flow region, implemented by the coupled Laminar Flow interface, and Darcy’s law, implemented by the coupled Darcy’s Law interface, to describe the flow in the porous region.
Here ρns and
uns are the density and velocity on the free-flow side of the interface,
ρd and
ud the density and velocity on the porous side, and
n is a vector normal to the interface. In addition the coupling enforces the balance of the normal forces by:
where pns and
pd are the pressure on the free-flow side and porous side of the interface, respectively, and
K is the viscous stress tensor (defined only on the free-flow side).
where aBJ is the Beavers and Joseph parameter,
κ is the permeability tensor of the porous medium (defined on the porous side of the interface),
μns is the fluid’s dynamic viscosity on the free-flow side of the interface, and
n is the number of space dimensions.
For cases when the permeability tensor is not isotropic, the Use projected permeability option allows to take into account only the permeability in the direction of the tangential velocity component. This is accomplished by replacing the
term on the rights hand side of
Equation 7-38 and
Equation 7-39 by:
with t a unit vector tangent to the interface for 2D and 2D-axisymmetric cases, and for 3D cases by:
The Viscous slip condition allows for a more general coupling condition. This interface condition is given by:
Here Ls is a slip length, and
ub a user-defined interfacial velocity.