The Two-Phase Darcy’s Law (tpdl) interface (), found under the Porous Media and Subsurface Flow branch () when adding a physics interface, is used to simulate fluid flow through interstices in a porous medium. It solves Darcy’s law for the total pressure and the transport of the fluid content for one fluid phase. The physics interface can be used to model low velocity flows or media where the permeability and porosity are very small, for which the pressure gradient is the major driving force and the flow is mostly influenced by the frictional resistance within the pores. The physics interface can be used for stationary and time-dependent analyses.

When this physics interface is added, the following default nodes are also added in the Model Builder — Fluids and Matrix Properties, No Flow (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and mass sources. You can also right-click Two-Phase Darcy’s Law to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is tpdl.

Enter a Reference pressure level pref (SI unit: Pa). The default value is 1[atm].

The dependent variables (field variables) are the Pressure and Fluid content 1. The name can be changed but the names of fields and dependent variables must be unique within a component.

To display this section, click the Show More Options button () and select Stabilization from the Show More Options dialog box.

There are two consistent stabilization methods available — Streamline diffusion and Crosswind diffusion. Streamline diffusion is active by default. The Residual setting applies to both the consistent stabilization methods. Approximate residual is the default setting and it means that derivatives of the capillary diffusion tensor components are neglected. This setting is usually accurate enough and computationally faster. If required, select Full residual instead.

You can choose the order of the shape functions used for the pressure and fluid content variables solved by the Two-Phase Darcy’s Law interface. The default shape functions are P2+P1 Lagrange.

To display all settings available in this section, click the Show More Options button () and select Advanced Physics Options from the Show More Options dialog box.