The Free and Porous Media Flow, Darcy interface () combines the Darcy’s Law and Laminar Flow interfaces to compute fluid velocity and pressure fields where free flow is connected to porous media. The physics interface is suited for situations when both the free flow and the flow in the porous media are laminar.

When a predefined Free and Porous Media Flow, Darcy interface is added from the Porous Media and Subsurface Flow branch () of the Model Wizard or Add Physics window, the Darcy’s Law and Laminar Flow interfaces are added to the Model Builder. In addition, the Multiphysics node is added, which automatically includes the Free and Porous Media Flow Coupling multiphysics coupling.

The Darcy’s Law interface is used to simulate fluid flow through interstices in a porous medium. It can be used to model low-velocity flows in media where the permeability and porosity are very small, and for which the pressure gradient is the major driving force and the flow is mostly influenced by the frictional resistance within the pores.

The Laminar Flow interface is used to compute the velocity and pressure for a fluid flow in the laminar flow regime. A flow will remain laminar as long as the Reynolds number is below a certain critical value. At higher Reynolds numbers, disturbances have a tendency to grow and cause transition to turbulence.

When physics interfaces are added using the predefined couplings, for example Free and Porous Media Flow, Darcy, specific settings are included with the physics interfaces and the coupling features.