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  1. Properties used in PHOENICS
    1. The list of properties
    2. The indirect and direct ways of setting properties
    3. The three main methods of writing the input file
  2. Setting properties by selecting materials
    1. When one material fills the whole domain
    2. When different parts of the domain are occupied by different materials
  3. Setting individual properties
    1. When one material fills the whole domain
      1. Setting uniform properties
      2. Setting properties which vary in accordance with formulae coded in GXname files
      3. Using In-Form
      4. Using PLANT
      5. Introducing user's-own Fortran
    2. When different parts of the domain are occupied by different materials

1. Properties used in PHOENICS

1.1 The list of properties

The properties of materials which are relevant to flow simulations are:

The following table lists the properties used in PHOENICS, with their PIL-variable names and their SI units.

PIL variableSI unitsnature
RHO1 kg/m**3 phase-1 density
DRH1DP m**2/Newton proportionate change of RHO1 with pressure
RHO2 kg/m**3 phase-2 density
DRH2DP m**2/Newton proportionate change of RHO2 with pressure
ENUL m**2/skinematic laminar (reference) viscosity
ENUT m**2/s kinematic turbulent contribution to effective viscosity
PRNDTL(indvar) dimensionless,if >0 Prandtl or Schmidt number
PRNDTL(indvar) watts/(m*degC), if <0 and if indvar is enthalpy or temperature, thermal conductivity
PRNDTL(indvar) kg/m*s, if <0 and if indvar is not enthalpy or temperature, exchange coefficient
PRT(indvar) dimensionless turbulent contribution to the effective Prandtl or Schmidt number
PHINT(indvar) according to indvar equilibrium interface value for phase 1
PHINT(indvar) according to indvar equilibrium interface value for phase 2
TEM1 or TMP1 degCelsiusphase-1 temperature
TEM2 or TMP2 degCelsiusphase-2 temperature
EL1 mphase-1 turbulence length
EL2 mphase-2 turbulence length
CP1 joule/(kg*degC) constant-pressure specific heat of phase 1
CP2 joule/(kg*degC) constant-pressure specific heat of phase 2
DVO1DT 1/degC proportionate change of first-phase specific volume (i.e 1/RHO1) with temperature
DVO2DT 1/degC proportionate change of second-phase specific volume (i.e. 1/RHO2) with temperature
EMISS 1/m absorptivity = proportion of radiation which is absorbed per unit length
SCATT 1/m proportion of radiation which is scattered per unit length
CFIPS Newton*s/m**4 momentum-transfer rate from one phase to another per unit volume and per unit of velocity difference
CMDOT kg*s/m**4 mass-transfer rate per unit volume and per unit of velocity difference
CINT(indvar) dimensionlessratio of exchange coefficient to inter-phase friction factor for phase-1 side of interface
CINT(indvar) dimensionlessratio of exchange coefficient to inter-phase friction factor for phase-2 side of interface
CVM dimensionlessvirtual-mass coefficient for two-phase flow.

The same properties are listed also at the top of the open-source Fortran file gxprutil.for, which lists in addition:

the indices

by which they are referred to in EARTH and GROUND coding and, the relevant cases, in the PROPS file.

1.2 The indirect and direct ways of setting properties

Properties can be set in one or other of two ways, namely:
  1. indirectly, by naming the fluids and/or solids which are present, and stating what parts of the domain they occupy.

    Then, if PHOENICS recognises the names, it will evaluate and use the properties which prevail at each location from the corresponding formulae;
    and also (when the formulae make reference to them) from the prevailing:
    temperature, pressure and concentrations.

  2. directly, by specifying the properties individually, either as constants or by way of formulae, and then specifying the places where each is to be evaluated.
Method a is often the simpler; for PHOENICS is supplied with property formulae for a large number of commonly-arising materials.

Method b is the more flexible; for it allows arbitrary (combinations of) properties to be investigated, whether or not materials possessing them actually exist.

Both ways can be employed during the course of the same simulation. For example, some parts of the domain can be occupied by named materials, while other parts are occupied by materials of which the properties are set individually.

The material-property information is stored in PHOENICS in two places, namely:

  1. The PROPS file, which:

  2. The core library case 089, which:

Both are ASCII files which may be edited by users who wish to supply additional entries.

1.3 The three main methods of writing the input file

As explained in PHOENICS Overview (TR001), what PHOENICS does is controlled by an input-data file called Q1; and of the several methods provided for writing this file the most frequently used are:

In the present article, attention will be focussed on what the Q1 should contain, no matter which method is used. However, a full account of the setting of properties by the menu-interactive method can be found in the appropriate section of TR 326.

2. Setting properties by selecting materials

2.1 When one material fills the whole domain

(a) If the older selection-by-number method is employed, the following statement in the Q1-file suffices:

SETPRPS(argument1, argument2)


For example:


dictates that the properties will be those of atmospheric air, because that is the significance of IMAT=0 .



would set the second-phase fluid to be water with the properties pertaining to 20 degrees Celsius.

Then the Q1EAR file, which is created at the end of a SATELLITE run records in a structured manner what information (including defaults) will be sent to the solver module, EARTH, contains the lines:

  Group 9. Properties
 RHO1    = 1.189000E+00
 RHO2    = 9.982300E+02
 DVO2DT  = 1.180000E-04 ;DRH2DP = 0.000000E+00
 ENUL    = 1.544000E-05
 CP1     = 1.005000E+03 ;CP2    = 4.181800E+03
and the EARDAT file, which conveys the same information in more condensed form, contains the lines:

 DOMAIN    PHASE_1_MAT    I       0
 DOMAIN    PHASE_2_MAT    I      67
which are reflected in the RESULT file as:
 Group 19. EARTH Calls To GROUND Station
 USEGRD  =    T  ;USEGRX =    T
These lines signify that, for the whole domain of simulation, the first-phase material has the properties associated with material 0 of the PROPS file. while the second-phase material has the properties of material 67.

It should be remarked the, since version 3.4.2, Earth no longer makes specific use of the domain-fluid concept, but picks up all the information which it needs from other EARDAT items.

(b) If the newer In-Form-based selection-by-name method is employed, the following lines could be placed in the Q1-file in order to select, for example, mercury as the phase-1 fluid:


Then the Q1EAR, EARDAT and RESULT files would all contain copies of the formulae which EARTH will use for the computation of density. specific heat, viscosity and thermal conductivity.

The EARDAT version is:

 PROPERTY  RHO1           C=POL3(TEM1&14.293&-2.68226&5.3957$
 PROPERTY  RHO1           CE-4&-3.16674E-7)
 PROPERTY  ENUL           C=POL3(TEM1&5.47854&-.02372&4.3529$
 PROPERTY  ENUL           C9E-5&-2.79475E-8)/(-10110)
 PROPERTY  CP1            C=POL3(TEM1&159.54&-.10108&1.23163$
 PROPERTY  CP1            CE-4&-3.60116E-8)
 STORED    COND           C=POL3(TEM1&3.90003&.01799&-8.2070$
 STORED    COND           C1E-6&1.52734E-9)

Here the 'POL3' and 'TEM1' are clues indicating that third-order polynomials are to be used for each of RHO1, ENUL, CP1 and COND, these being the formulae which are to be found in the loaded input-library case 089.

In-Form's case 089 refers only to phase-1 fluids. The just-described lines will therefore dictate that mercury is the first-phase fluid.

Of course it can easily be modified to allow phase-2 fluids to be selected.

Input-Library cases which illustrate this mode of property setting are 761 and 762.

(c) The phrase "one material fills the whole domain" does not, it should be mentioned, preclude the presence of "blocked-off" regions, which the material does not occupy, provided that whatever is contained in those regions is without influence on the phenomena being simulated other than, perhaps, to impose the no-slip condition at their boundaries.

Such regions are indicated by possession of PRPS values (see below) equal to:

2.2 When different parts of the domain are occupied by different materials

It frequently occurs that PHOENICS is required to simulate flow and heat transfer in circumstances in which solid bodies are present. Often these solids interact thermally with the fluids.

Moreover, different parts of the domain may be occupied by different fluids, as when a glass bottle containing hot water is cooled by contact with external air.

This requirement is met by assigning different IMAT values to the spaces which each material occupies. Specifically:-

Example: core library case 922

This case does indeed illustrate what happens when a heated steel block is suspended in a bath of cooling water.

The following three images show:

It happens that case 922 is a variant of core library case 921, inspection of which shows that the STORE(PRPS) and FIINIT(PRPS) settings have actually been effected by the use of PIL macros.

The lines in 921.htm which set the materials, and therefore their properties, are simply:

in which:
is a character variable, set in always-loaded macro 014 to $072
macro 072
loads the macros
( = $071) and 'solidmat' ( = $070), both of which issue the STORE(PRPS) command
is a character variable defined in macro 014 and set equal to FIINIT(PRPS)
is an integer defined in fluidmat as 67
is an integer defined in solidmat as 111

Users are of course free to edit any of these macros, or create new ones, for their personal convenience.

3. Setting individual properties

3.1 When one material fills the whole domain

3.1.1 Setting uniform properties

When the properties are uniform, i.e. have the same magnitudes everywhere (except in blocked regions), all that is needed is for the Q1 to contain statements of the kind:

PIL_name_of_property = value of property.

Examples are:

RHO1 = 1.189
CP1 = 1000.0
ENUL = 1.E-5
CFIPS = 100.0
CMDOT = 0.01

It is of course the user's responsibility to choose the values which meet his or her needs, and to maintain consistency of units.

The values which appear in the Q1 file are echoed in the Q1EAR, in EARDAT and in RESULT.

3.1.2 Setting properties which vary in accordance with formulae coded in GXname files

Properties which vary, for example as functions of temperature, pressure or composition, can be specified, in many cases by:

Further examples may be inspected by clicking on the RHO1 above, and on the following variable names, grouped in accordance with whether they relate to:

3.1.3 Using In-Form

The method of setting non-uniform properties by way of formulae placed in the Q1 file is explained fully in the PHOENICS Encyclopaedia article on In-Form, which there is no need to recapitulate.

Two sections are of especial relevance, namely:

A library case which illustrates the use of such formulae is 763, in which a variety of nearly-equivalent formulae for the same fluid are shown to produce (of course) almost the same flow fields.

3.1.4 Using PLANT

Before In-Form became available, the most convenient method of introducing property formulae which were not represented in the GXx subroutines was to make use of PLANT.

This method is still available. It is described in detail here.

3.1.5 Introducing user's-own Fortran

Before PLANT was introduced, users wishing to introduce novel material properties would do so by introducing their own coding into the user-accessible GROUND sub-routine.

This method is also still available, and is described on-line here.

3.2 When different parts of the domain are occupied by different materials

As explained above, the presence of different materials in different locations is conveyed to the PHOENICS solver by ascribing to each cell a value of the PRPS variable.

This is done by setting initial values, via FIINIT and INIT, for steady-flow cases; and for transient flows also if the materials do not move their positions.

Wherever the PRPS value is one of those listed in the PROPS file supplied by CHAM, or in another referred to by the user, the values of the properties which are used by the solver are those in the file, as has already been described.

However, wherever the PRPS has been set equal to -1.0 , the solver uses the values of the properties which correspond to the PIL variables RHO1, ENUL, CP1, etcetera.

Often this is achieved by setting FIINIT(PRPS) = -1.0, and using INIVAL-type patches for all regions occupied by recognised materials. However, how the PRPS field is set is immaterial; it is only the value in the cell which matters.

Of course, when objects move their positions relative to the computational grid, their motion must be reflected by changes in the PRPS values of the affected cell.

Two further remarks should be made concerning recently-introduced features of PHOENICS, namely PARSOL and In-Form. They are:

  1. PARSOL (an abbreviation for partial solids) has been introduced so as to allow for solid objects of which the boundaries do not coincide with cell boundaries.

    For example, a solid sphere may be immersed in a stream of air; and a cartesian grid may be used for the computation. Then some of its cells have their faces intersected by the surface of the sphere.

    These so-called 'cut-cells' contain two materials, not one.

    When the solver detects such cells, it sets PRPS equal to the value appropriate to the fluid. This may be -1, which is the case when the PIL variables are being used to define properties. Otherwise it will be a value appearing in the PROPS file

    Only the cells which lie wholly within the enclosing surface of the solid retain the PRPS value which was assigned to the object.

  2. When properties are being assigned by way of the In-Form (PROPERTY .... command, the properties dictated by the formulae are applied by default to all cells of the grid.

    If therefore this is undesired (as is usual when solids are immersed in a fluid), application of the formula must be specifically excluded by use of the 'with' condition.