Encyclopaedia Index

PHI, the variable name

PHI is a term used in the PHOENICS documentation to name, generically, the conserved quantities for which PHOENICS solves.

These quantities are referenced, in PIL, by use of a name of up to four characters. Each name has an associated integer ( 1 through 150 ) which is used to determine the storage location for the conserved quantity.

For example, the first-phase velocity has the default name, U1, and resides in store number 3. The name used to denote this velocity may be changed to to UVEL (say) by use of the NAME command, i.e. NAME(U1)=UVEL (or NAME(3)=UVEL).

The default names are:
1 P1 First-phase pressure.
2 P2 Second-phase pressure (inactive).
3 U1 First-phase x-direction velocity.
4 U2 Second-phase x-direction velocity.
5 V1 First-phase y-direction velocity.
6 V2 Second-phase y-direction velocity.
7 W1 First-phase z-direction velocity.
8 W2 Second-phase z-direction velocity.
9 R1 First-phase volume fraction.
10 R2 Second-phase volume fraction.
11 RS Second-phase shadow volume fraction.
12 KE Kinetic energy of turbulence for the first phase.
13 EP Rate of dissipation of turbulence kinetic energy of the first phase.
14 H1 First-phase enthalpy.
15 H2 Second-phase enthalpy.
16 C1 First-phase concentration variable.
17 C2 Second-phase concentration variable.
18 C3 Another first-phase concentration variable.
19 C4 Another second-phase concentration variable.
49 C34 Another second-phase concentration variable.
50 C35 Another first-phase concentration variable.

Variables with sequence numbers greater than 51 all have the default name CHAM

The complete set of variables with their current names can be displayed by means of the command VARIABLES.

The attachment of any variable to a particular phase can be changed by means of the TERMS command.

See also the individual entries for P1....H2, NAME and NPHI.


---------------------------------------- Photon Help ----

PHI.... is used to specify the name of a PHOENICS PHI or PHIDA file which PHOTON will attach. Before loading the grid, PHOTON enables you to specify grid scaling factors. If the file is for a BFC run, PHOTON will prompt for the name of an XYZ file. Entering a slash '/' in response to the filename prompt will abort the file-opening command.

See also : XYZ

NEW!:PICS -------------------------------------------------- PICS

PICS (PHOTON Internal Coordinate System) is the coordinate system used by PHOTON to draw graphical elements (line, text etc) on output devices. It is a two-dimensional system (say x-y), with the origin located at the bottom left-hand corner of the display are (eg, the screen or paper). The coordinates used are normalised to the ranges 0 to 4095 (in the x direction) and 0 to 3120 (in the y direction).

PICS units are used to specify the position of the text drawn through the TEXT command (when issued within a USE file), and the geometry features drawn through the GEOMETRY command.



------------------------------------ Photon Help ----

Enter the name of PHI(DA) file here.




----- PIL real array; group 9, sect 8, 9 - Satellite Help - default=-20202.0;

PHINT(phi)....interface value of the variable indicated.

PHINT is an array carrying a real-number value for each variable (i.e. phi ) which indicates, when two phases are present and interphase transport is active, what value prevails immediately at the interface on the side of the phase in question. For the purpose of interphase transport, the phases are treated in pairs. Thus U1 ( index no. 3 ) is paired with U2 (4), H1 (14) is paired with H2 (15). See TERMS for further information.

(a) When neither PHINT of the pair retains its default value,

If PHINT is given any value other than GRND (or GRND1, GRND2, etc), that value will be used for the interface value in calculation of the transfer rate between the bulk of the phase and the interface. Otherwise, EARTH will call GROUND group 9 section 8 (for phase 1), or section 9 (for phase 2), expecting to find that the user has provided an array of phi-values pertaining to the interface.

A common use of PHINT is for the specification of the interface enthalpies of (say) steam and water as being those valid for thermodynamic equilibrium at the prevailing pressure.

If the pressure is almost uniform through the field, the use of constant values of PHINT will suffice; but varying pressure would dictate the use of PHINT=GRND, because the pressure influencing the saturation enthalpies can be known only during the course of the calculation.

The options provided in GREX are as follows:

PHINT(H1)=GRND1 selects the interface value of H1 equal to,
HUNIT*( PHNH1A*(pressure+PRESS0)**PHNH1B + PHNH1C ) .

PHINT(H2)=GRND1 selects the interface value of H2 equal to,
HUNIT*( PHNH2A*(pressure+PRESS0)**PHNH2B + PHNH2C ) .

PHINT(H2)=GRND2 selects the interface value of H2 equal to,
PHNH2A + PHNH2B * ( interface value of H1 ) .

Usually the transfer rates on the two sides of the interface are different; and often the interphase mass-transfer rate depends on the difference. In such a case, the HEATBL option for the mass- transfer rate is appropriate. See HEATBL for explanation.

(b) When either of the PHINTs retains its default value.

Three "floating-interface" conditions are provided for.

** When both PHINTs retain their default values, the transport from one phase to the other is given as the product of the harmonic mean of the transfer coefficients on each side of the interface ( denoted COI1 and COI2 ), and the difference between the bulk values of each phase, eg for enthalpy: (2/( 1/COI1 + 1/COI2 )) * (H1-H2)

** When the PHINT of the first variable is the default and the second has the value V, the flux is modified to: (2/( 1/COI1 + 1/COI2 )) * (H1-H2+V) Here V represents a "jump" condition at the interface.

** When the PHINT of the second variable is the default and the first has the value V, the flux is modified to: (2/(1/(COI1*V) + 1/COI2 )) * (H1/V-H2) Here V is set to, ( interface value of H1 ) / ( interface value of H2 ).

The coefficients COI1 and COI2 are given by the following formulae:
COI1=CINT(phi1)*FIP, and
COI2=CINT(phi2)*FIP, where FIP is the reference transport coefficient determined by the setting of CFIPS.

When CINT(phi1)=GRND, COI1= the GROUND-set magnitude.
When CINT(phi2)=GRND, COI2= the GROUND-set magnitude.

See the CINT entry for further information.