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 Turbulent Flow interfaces, the Fluid Properties node also adds the equations for the turbulence transport equations.

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, the Specify dynamic viscosity (default) and Inelastic non-Newtonian options are available. Use the default option to either get the dynamic viscosity from a material, or to add a user defined expression. The Inelastic non-Newtonian option includes several inelastic non-Newtonian models for the relationship between the shear stress and shear rate.

If the Specify dynamic viscosity option is selected, an inelastic non-Newtonian model can be selected by adding the corresponding Material Properties group as a subnode to a material node.

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, Bingham–Papanastasiou, Herschel–Bulkley–Papanastasiou and Casson–Papanastasiou.

The following parameters are required for the Power law:

For the Carreau model, the following parameters are required:

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

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

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

The default values for the parameters are listed in Table 3-2.

For the Turbulent Flow, k-ε, Turbulent Flow, k-ω, and Rotating Machinery, Turbulent Flow k-ε interfaces, an upper limit on the mixing length is required.

When the Mixing length limit lmix,lim is set to Automatic, it is evaluated to the shortest side of the geometry bounding box. If the geometry is, for example, a complicated system of slim entities, this measure can be too high. In such cases, it is recommended that the mixing length limit is defined manually.

For the Turbulent Flow, Low Re k-ε; Turbulent flow, Algebraic yPlus; Turbulent Flow, L-VEL; Turbulent Flow, SST; Turbulent Flow, Spalart–Allmaras; and Turbulent Flow, v2-f interfaces, a Wall Distance interface is included.

When the Reference length scale lref is set to Automatic, it is evaluated to one tenth of the shortest side of the geometry bounding box. The solution to the wall distance equation is controlled by the parameter lref. The distance to objects larger than lref is represented accurately, while objects smaller than lref are effectively diminished by appearing to be farther away than they actually are. This is a desirable feature in turbulence modeling because small objects would have too large an impact on the solution if the wall distance were measured exactly. The automatic value is usually a good choice but the value can become too high if the geometry consists of several slim entities. In such cases, it is recommended that the reference length scale is defined manually.