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. The consistent interface allows different fluids to be used in an input file by simply swapping the name of the Fluid Properties UserObject in a plug-and-play manner.

Fluids available

This module provides fluid properties for many different gases, liquids and mixtures.

Available Objects and Subsystems

Properties available

Each FluidProperties UserObject above provides access to several fluid properties. Two main formulations are available using

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

  • (p, T) - pressure and temperature

although some fluid properties may be available in terms of other primary variables. Depending on the actual fluid implementation, any number of the following fluid properties may be available.

  • Density: rho_from_p_s(pressure, entropy)

  • Density: rho_from_p_T(pressure, temperature)

  • Dynamic viscosity: mu_from_v_e(volume, energy)

  • Dynamic viscosity: mu_from_p_T(pressure, temperature)

  • Enthalpy: h_from_p_T(pressure, temperature)

  • Enthalpy: h_from_T_v(temperature, volume)

  • Fluid name: fluidName()

  • Gibbs free energy: g_from_v_e(volume, energy)

  • Internal energy: e_from_v_h(volume, enthalpy)

  • Internal energy: e_from_p_rho(pressure, density)

  • Internal energy: e_from_T_v(temperature, volume)

  • Internal energy: e_from_p_T(pressure, temperature)

  • Isobaric specific heat: cp_from_v_e(volume, energy)

  • Isobaric specific heat: cp_from_p_T(pressure, temperature)

  • Isochoric specific heat: cv_from_v_e(volume, energy)

  • Isochoric specific heat: cv_from_T_v(temperature, volume)

  • Isochoric specific heat: cv_from_p_T(pressure, temperature)

  • Molar mass (kg/mol): molarMass()

  • Pressure: p_from_v_e(volume, energy)

  • Pressure: p_from_T_v(temperature, volume)

  • Pressure: p_from_h_s(pressure, entropy)

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

  • Ratio of specific heats: gamma_from_p_T(pressure, temperature)

  • Specific entropy: s_from_v_e(volume, energy)

  • Specific entropy: s_from_p_T(pressure, temperature)

  • Specific entropy: s_from_h_p(enthalpy, pressure)

  • Specific entropy: s_from_T_v(temperature, volume)

  • Specific volume: v_from_p_T(pressure, temperature)

  • Speed of sound: c_from_v_e(volume, energy)

  • Speed of sound: c_from_p_T(pressure, temperature)

  • Temperature: T_from_v_e(volume, energy)

  • Temperature: T_from_p_h(pressure, enthalpy)

  • Thermal conductivity: k_from_v_e(volume, energy)

  • Thermal conductivity: k_from_p_T(pressure, temperature)

  • Thermal expansion coefficient: beta_from_p_T(pressure, temperature)

Derivatives of fluid properties with respect to the primary variables are also available for several of the fluid properties listed above. These can be evaluated using the following notation: rho_from_p_T(p, T, rho, drho_dp, drho_dT) etc.


Fluid properties are now available using an interface suitable for use with MOOSE's Automatic Differentiation capability. See example in the next section.

The full list of available methods can be found in either the source code or the Modules Doxygen page for each FluidProperties class.


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 existing UserObject interface.


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.


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]);

In a similar fashion, fluid properties can be accessed using the Automatic Differentiation interface using the DualReal version which provides both the value and derivatives

DualReal rho = _fp.p_from_T_v(T, v);

where and are DualReal's. The result (density rho in this example) then contains both the value of density and its derivatives with respect to the primary variables T and v.

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 and overriding the methods that describe the fluid properties. These can then be used in an identical manner as all other Fluid Properties UserObjects.


Fluid Properties Interrogator

The FluidPropertiesInterrogator is a user object which can be used to query eligible fluid properties objects.

Additional objects

Several additional objects such as AuxKernels and Materials are provided:

Available Objects and Subsystems

  • Fluid Properties App
  • PressureAuxComputes pressure given specific volume and specific internal energy
  • SaturationTemperatureAuxComputes saturation temperature from pressure and 2-phase fluid properties object
  • SpecificEnthalpyAuxComputes specific enthalpy from pressure and temperature
  • StagnationPressureAuxComputes stagnation pressure from specific volume, specific internal energy, and velocity
  • StagnationTemperatureAuxComputes stagnation temperature from specific volume, specific internal energy, and velocity
  • TemperatureAuxComputes temperature given specific volume and specific internal energy

Available Objects and Subsystems