The Fluid Properties node adds the momentum and continuity equations solved by the physics interface, except for volume forces, which are added by the Volume Force feature. The node also provides an interface for defining the material properties of the fluid.

For the Viscoelastic Flow interface, the Fluid Properties node also adds the equations for the components of the elastic stress tensor.

By default, the Temperature model input is set to Common model input, and the temperature is controlled from Default Model Inputs under Global Definitions or by a locally defined Model Input. If a Heat Transfer interface is included in the component, it controls the temperature Common model input. Alternatively, the temperature field can be selected from another physics interface. All physics interfaces have their own tags (Name). For example, if a Heat Transfer in Fluids interface is included in the component, the Temperature (ht) option is available for T.

You can also select User defined from the Temperature model input in order to manually prescribe T.

The default Absolute pressure pA is p + pref, where p is the dependent pressure variable from the Navier–Stokes or RANS equations, and pref is from the user input defined at the physics interface level. When pref is nonzero, the physics interface solves for a gauge pressure. If the pressure field instead is an absolute pressure field, pref should be set to 0.

The Absolute pressure field can be edited by clicking Make All Model Inputs Editable () and entering the desired value in the input field.

The density can either be specified by a material, or by a User defined expression. The density in a material can depend on temperature and pressure, and these dependencies are automatically replaced by pref for weakly compressible flows and pref and Tref for incompressible flows (as specified by the Compressibility setting at the physics interface level). If density variations with respect to pressure are to be included in the computations, Compressibility must be set to compressible. Any dependencies in the density on quantities other than temperature and pressure must be consistent with the Compressibility setting at the interface level.

For laminar flow, Newtonian and Inelastic non-Newtonian constitutive relations are available. Newtonian fluids have a linear relationship between the shear stress and the shear rate.

The Dynamic viscosity μ describes the relationship between the shear rate and the shear stresses in a fluid. Intuitively, water and air have low viscosities, and substances often described as thick (such as oil) have higher viscosities.

Non-Newtonian fluids are encountered in everyday life and in a wide range of the industrial processes. Examples of non-Newtonian fluids include yogurt, paper pulp, and polymer suspensions. Such fluids have a nonlinear relationship between the shear stress and the share rate. The following inelastic non-Newtonian models are available: Power law, Carreau, Carreau–Yasuda, Cross, Cross–Williamson, Sisko, Bingham–Papanastasiou, Herschel–Bukley–Papanastasiou, Casson–Papanastasiou, DeKee–Turcotte–Papanastasiou, Robertson–Stiff–Papanastasiou, Ellis, and Houska thixotropy.

The following parameters are required for the Power law:

For the Carreau model, the following parameters are required:

For the Carreau-Yasuda model, the following parameters are required:

For the Cross model, the following parameters are required:

For the Cross-Williamson model, the following parameters are required:

For the Sisko model, the following parameters are required:

For the Bingham–Papanastasiou model, the following parameters are required:

For the Herschel–Bukley–Papanastasiou model, the following parameters are required:

For the Casson–Papanastasiou model, the following parameters are required:

For the DeKee–Turcotte–Papanastasiou model, the following parameters are required:

For the Robertson–Stiff–Papanastasiou model, the following parameters are required:

For the Ellis model, the following parameters are required:

For the Houska thixotropy model, the following parameters are required:

The default values for the parameters are listed in Table 3-1.

If μ0, μp, m, or μDK is User defined, or the Houska thixotropy model is used, the thermal effects are activated with five options: None, Arrhenius, Williams–Landel–Ferry (WLF), Exponential, and User defined.