Fluid Properties Module

The Fluid Properties module provides a consistent interface to fluid properties such as density, viscosity, enthalpy and many others, as well as derivatives with respect to the primary variables. This allows different fluids to be used in the input files by simply swapping the name of the Fluid Properties UserObject in a plug-and-play manner.


Fluid properties are implemented in GeneralUserObjects that have empty initialize(), execute() and finalize() methods, so do nothing during a simulation. Their purpose is to provide convenient access to fluid properties through the UserObject interface.

This module provides fluid properties for different liquids and gases.

Provided formulations are available in terms of:

  • (p, T) - pressure and temperature

  • (v, e) - specific volume and specific internal energy

Energy-volume formulation

For the energy-specific volume formulation, the following properties (with corresponding method names) are provided:

  • Pressure: pressure(volume, energy)

  • Temperature: temperature(volume, energy)

  • Speed of sound: c(volume, energy)

  • Isobaric specific heat: cp(volume, energy)

  • Isochoric specific heat: cp(volume, energy)

  • Ratio of specific heats: gamma(volume, energy)

  • Dynamic viscosity: mu(volume, energy)

  • Thermal conductivity: k(volume, energy)

  • Specific entropy: s(volume, energy)

  • Density: rho_from_p_T(pressure, temperature)

  • Enthalpy: h(pressure, temperature)

  • Internal energy: e(pressure, density)

  • Thermal expansion coefficient: beta(pressure, temperature)

  • Pressure (from enthalpy and entropy): p_from_hs(enthalpy, entropy)

UserObjects available in the FluidProperties module that use the internal energy-volume formulation are

Pressure-temperature formulation

A separate formulation based on pressure (Pa) and temperature (K) is also provided. For the pressure-temperature formulation, the available properties (with corresponding method names) are:

  • String representing fluid name: fluidName()

  • Molar mass (kg/mol): molarMass()

  • Density (kg/m): rho_from_p_T(pressure, temperature)

  • Internal energy (J/kg): e(pressure, temperature)

  • Enthalpy (J/kg): h(pressure, temperature)

  • Specific entropy (J/kg/K): s(pressure, temperature)

  • Dynamic viscosity (Pa.s): mu(pressure, temperature) or mu(density, temperature)

  • Thermal conductivity (W/m/K): k(pressure, temperature) or k(density, temperature)

  • Isobaric specific heat (J/kg/K): cp(pressure, temperature)

  • Isochoric specific heat (J/kg/K): cv(pressure, temperature)

  • Ratio of heat capacites (-): gamma(pressure, temperature)

  • Thermal expansion coefficient (-): beta(pressure, temperature)

  • Henry's law constant (1/Pa): henry(temperature)

Available fluids are:


All Fluid Properties UserObjects can be accessed in MOOSE objects through the usual UserObject interface. The following example provides a detailed explanation of the steps involved to use the Fluid Properties UserObjects in other MOOSE objects, and the syntax required in the input file.

This example is for a problem that has energy-volume as the primary variables. A material is provided to calculate fluid properties at the quadrature points.

For problems that use the pressure-temperature formulation, the procedure for using the Fluid Properties UserObjects is identical, apart from a change in the base class name (from SinglePhaseFluidProperties to SinglePhaseFluidPropertiesPT).


To access the fluid properties defined in the Fluid Properties module in a MOOSE object, the source code of the object must include the following lines of code.

In the header file of the material, a const reference to the base SinglePhaseFluidProperties object is required:

  const SinglePhaseFluidProperties & _fp;

A forward declaration to the SinglePhaseFluidProperties class is required at the beginning of the header file.

class SinglePhaseFluidProperties;

In the source file, the SinglePhaseFluidProperties class must be included

#include "SinglePhaseFluidProperties.h"

The Fluid Properties UserObject is passed to this material in the input file by adding a UserObject name parameters in the input parameters:

  params.addRequiredParam<UserObjectName>("fp", "The name of the user object for fluid properties");

The reference to the UserObject is then initialized in the constructor using


The properties defined in the Fluid Properties UserObject can now be accessed through the reference. In this material, the computeQpProperties method calculates a number of properties at the quadrature points using the values of _v[_qp] and _e[_qp].

  _p[_qp] = _fp.p_from_v_e(_v[_qp], _e[_qp]);
  _T[_qp] = _fp.T_from_v_e(_v[_qp], _e[_qp]);
  _c[_qp] = _fp.c_from_v_e(_v[_qp], _e[_qp]);
  _cp[_qp] = _fp.cp_from_v_e(_v[_qp], _e[_qp]);
  _cv[_qp] = _fp.cv_from_v_e(_v[_qp], _e[_qp]);
  _mu[_qp] = _fp.mu_from_v_e(_v[_qp], _e[_qp]);
  _k[_qp] = _fp.k_from_v_e(_v[_qp], _e[_qp]);
  _g[_qp] = _fp.g_from_v_e(_v[_qp], _e[_qp]);

Input file syntax

The Fluid Properties UserObjects are implemented in an input file in the Modules block. For example, to use the ideal gas formulation for specific volume and energy, the input file syntax would be:

      type = IdealGasFluidProperties
      gamma = 1.4
      R = 8.31

In this example, the user has specified a value for gamma (the ratio of isobaric to isochoric specific heat capacites), and R, the universal gas constant.

The fluid properties can then be accessed by other MOOSE objects through the name given in the input file.

    type = FluidPropertiesMaterial
    e = e
    v = v
    fp = ideal_gas

Due to the consistent interface for fluid properties, a different fluid can be substituted in the input file be changing the type of the UserObject. For example, to use a stiffened gas instead of an ideal gas, the only modification required in the input file is

      type = StiffenedGasFluidProperties
      gamma = 2.35
      q = -1167e3
      q_prime = 0
      p_inf = 1.e9
      cv = 1816

      mu = 0.9
      k = 0.6

Creating additional fluids

New fluids can be added to the Fluid Properties module by inheriting from the base class appropriate to the formulation and overriding the methods that describe the fluid properties. These can then be used in an identical manner as all other Fluid Properties UserObjects.

Objects, Actions, and Syntax