4.5. Fluid

The fluid pane is used to select the models and parameters defining the fluid phase. The fluid pane is only accessible if the fluid phase is being solved.

Name The name used to refer to the continuous phase in the GUI. By default, the continuous phase is termed “fluid”, However, it may be renamed for convenience.

4.5.1. Fluid Model Options

Solve Momentum Equation By default, all momentum equations are solved. Individual momentum equations may be disabled by toggling the check box.

Solve Species Equations By default, species transport equations are not solved for the fluid phase. If species equations are enabled, species will need to be added to the fluid phase using the fluid species tool.

Enable Scalar Equations By default, no additional scalar transport equations are solved with the fluid phase. Additional scalars may be added by toggling the scalar checkbox and specifying the number of additional scalars to track.

Energy Equations Energy equations cannot be enabled or disabled on a per-phase basis. As such, they are enabled or disabled for all phases in the Model Setup pane.

4.5.2. Fluid Properties

Density has units of \((\frac{kg}{m^3})\) and may be specified using one of the following approaches.

  • Constant:

    • A positive (non-zero) number must be provided.

  • Ideal gas law

    • Requires fluid temperature be specified for the whole domain and all flow boundary conditions.

    • Requires a fluid molecular weight.

  • User-Defined Function (UDF)

    • A custom equation of state must be provided in the usrproperties.f

    • A custom solver must be built.

Viscosity has units of \((Pa \cdot sec)\) and may be specified using one of the following approaches.

  • Constant:

    • A positive (non-zero) number must be provided.

  • Sutherland’s law

    • Requires fluid temperature be specified for the whole domain and all flow boundary conditions.

  • User-Defined Function (UDF)

    • A custom equation of state must be provided in the usrproperties.f

    • A custom solver must be built.

Molecular Weight has units of \((\frac{kg}{kmol})\) and may be specified using one of the following approaches.

  • Constant:

    • A positive (non-zero) number must be provided.

  • Mixture

    • Requires fluid species definition.

    • Requires fluid species mass fractions specification for the whole domain and all flow boundary conditions

Specific Heat has units of \((\frac{J}{kg \cdot K})\) and may be specified using one of the following approaches.

  • Constant:

    • A positive (non-zero) number must be provided.

  • Mixture

    • Requires fluid species definition.

    • Requires fluid species mass fractions specification for the whole domain and all flow boundary conditions

  • User-Defined Function (UDF)

    • A custom equation of state must be provided in the usrproperties.f

    • A custom solver must be built.

Thermal Conductivity has units of \((\frac{W}{m \cdot K})\) may be specified using one of the following approaches.

  • Constant:

    • A non-negative number must be provided.

  • Dilute Mixture Approximation

    • Requires fluid temperature be specified for the whole domain and all flow boundary conditions.

  • User-Defined Function (UDF)

    • A custom equation of state must be provided in the usrproperties.f

    • A custom solver must be built.

Reference pressure has units of \((Pa)\) and is zero by default. A constant value may be specified to shift the simulation pressure prior to scaling.

Pressure scale factor is dimensionless and is one by default. A constant value may be specified to scale the simulation pressure.

\[P_{scaled} = \frac{P_{simulation} - P_{reference} }{ P_{scale factor}}\]

4.5.3. Fluid Model Species

Specie that comprise the fluid phase are summarized in the species overview table. New species are added by clicking the add button, add, at the top of the species table, and selecting one or more valid regions (see Fig. 4.6).