This node defines the material properties of the fluid of the Porous Medium, the Unsaturated Porous Medium, the Dual Porosity Medium, the Dual Permeability Medium, or the Unsaturated Porous Medium parent node.

The available options for the Fluid type are Incompressible, Compressible, Compressible, linearized, or Ideal gas. The selection determines how the density and compressibility of the fluid are set.

The default Reference density ρref uses values From material. For User defined enter another value or expression.

The default Density ρ uses values From material. For User defined enter another value or expression as a function of the absolute pressure. The compressibility of the fluid is computed from it.

The default Reference density ρref and the Fluid compressibility χf use values From material. For User defined enter another value or expression. The fluid density increases linearly as a function of the fluid pressure.

For Ideal gas it uses the ideal gas law to describe the gas density. In this case, specify the thermodynamics properties. Select a Gas constant type — Specific gas constant Rs (the default) or Mean molar mass Mn (SI unit: J/(mol·K)). For Mean molar mass the universal gas constant R = 8.314 J/(mol·K) is used as the built-in physical constant. For both properties, the defaults use values From material. For User defined enter another value or expression.

For all fluid types specify the Dynamic viscosity μ (SI unit: Pa·s) uses values From material. For User defined enter another value or expression.

The Polymer Flow Module allows the use of inelastic non-Newtonian models. For Darcian Flow, you can choose between two options: Specify dynamic viscosity (default) or Inelastic non-Newtonian. Use the default option to either get the dynamic viscosity from a material, or to add a user defined expression. The default option lets you either use the dynamic viscosity from a material or define it with a custom expression. The Inelastic non-Newtonian option provides several models and defines the Apparent shear rate.

The following inelastic non-Newtonian Models are available for the Fluid feature under the Porous Medium feature:

The setup of these models in porous media is similar to their definition under the Fluid Properties feature.

To define the apparent shear rate , either enter a user-defined expression for the correction factor (α) or choose the Capillary bundle approach from the list and provide a value for the Tortuosity factor (C).

A default Fluid node is automatically added to the Porous Medium, the Unsaturated Porous Medium, the Dual Porosity Medium, the Dual Permeability Medium, and the Unsaturated Dual Permeability Medium node.