.. _fluid:

.. include:: /icons.rst

=====
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.

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.


Fluid Properties
----------------

**Density** has units of :math:`({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 :math:`(Pa \cdot s)` 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 :math:`({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 :math:`({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 :math:`({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 :math:`(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.

.. math::

   P_{scaled} = {P_{simulation} - P_{reference}}/{P_{scale factor}}


Fluid species
-------------------

Species 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 :numref:`ic_region_select`).