Encyclopaedia Index

### D1DP

is an integer index used in GROUND for the derivative of the natural logarithm of first-phase density with respect to pressure, i.e. DRH1DP.

### D2DP

is an integer index used in GROUND for the derivative of the natural logarithm of second-phase density with respect to pressure, i.e. DRH2DP.

### DARCON

---- PIL real; default= 1.0E4; group 13 -

This is the constant used in the whole-field patch generated when DARCY is set to TRUE. It can be reset at any time before the DARCY command is issued.

### DARCY

----- PIL logical; default=F; group 13 --- -

DARCY.... may be set to true in order to simulate a flow in which Darcy's law applies. Such flows arise in porous media and other highly-resistive media. Since Darcy's law is of a Laplace-equation form, potential-flow phenomena may also be simulated by putting DARCY=T.

In the 3D case, DARCY=T is equivalent to the following commands.

SOLVE(U1,V1,W1)
TERMS (U1,Y,N,N,N,Y,N)
TERMS (V1,Y,N,N,N,Y,N)
TERMS (W1,Y,N,N,N,Y,N)
PATCH(DARCY,PHASEM,1,NX,1,NY,1, NZ,1,1)
COVAL(DARCY ,U1 , DARCON, 0.000E+00)
COVAL(DARCY ,V1 , DARCON, 0.000E+00)
COVAL(DARCY ,W1 , DARCON, 0.000E+00)

DARCON is a real variable, default value 1.0E4, which should be set to (laminar viscosity/permeability).

Thus, DARCY=T causes the velocities to be solved. It cuts out the convection and diffusion terms for economy. It introduces a whole-domain PATCH of type PHASEM in which 'high' resistances are set for the solved-for velocities. The user must ask for pressure to be solved by the command, SOLVE(P1) .

DARCY=T is the recommended way of solving potential flows in BFCs. When DARCY is used for potential-flow simulations, it is important to recognize that the velocity potential is the pressure (P1), divided by the resistance coefficient, DARCON.

### Darcy's law

(constant used in (see DARCON real, Group 13))

(simulation of flow with (see DARCY logical, Group 13))

### DatMaker

DatMaker is a utility which creates .dat files suitable for use with the PHOENICS Virtual-Reality User Interface, from possibly-defective STL files produced by CAD and architectural packages. For details of operation, see here. For more general information on importing CAD files, see here.

---- PIL logical; default=F; group 25 --- -

DBADJS....controls the print-out of the adjustments to pressure and velocities consequent upon the solution of the pressure-correction equation. DBGPHI(P1), DBGPHI(U1), etc must be set to identify those variables for which this print-out is required.

### DBCFIP

---- PIL logical; default=F; group 25 --- -

DBCFIP....gives print-out of the inter-phase friction coefficient.

### DBCMP2

---- PIL logical; default=F; group 25 --- -

DBCMP2....governs print-out from the subroutine which assembles the inter-phase fluxes.

### DBCMPE

---- PIL logical; default=F; group 25 --- -

DBCMPE....gives print-out of the east- and west-links and fluxes of the finite-domain equations at the current z slab. It is subordinate to DBCOMP and DBGPHI.

### DBCMPH

---- PIL logical; default=F; group 25 --- -

DBCMPH....gives print-out of the high- and low-links and fluxes of the finite-domain equations at the current z slab. It is subordinate to DBCOMP and DBGPHI.

### DBCMPN

---- PIL logical; default=F; group 25 --- -

DBCMPN....gives print-out of the north- and south-links and fluxes of the finite-domain equations at the current z slab. It is subordinate to DBCOMP and DBGPHI.

### DBCMPR

---- PIL logical; default=F; group 25 --- -

DBCMPR....gives information about the subroutine which adjusts the volume fractions to make them add up to 1, and which calculates the contribution of phase diffusion to the convective fluxes. It is subordinate to DBGPHI(R2). See also DBCOMP.

### DBCOMP

---- PIL logical; default=F; group 25 --- -

DBCOMP....controls print-out from the subroutine which sets up the finite-domain equations for each variable. See also DBGPHI and DBCMPE, DBCMPN and DBCMPH.

### DBCONT

---- PIL logical; default=F; group 25 --- -

DBCONT....provides debug from the contour-plotting subroutine.

### DBCONV

---- PIL logical; default=F; group 25 --- -

DBCONV....gives print-out of the convection fluxes for phase 1 when DBGPHI(R1) is T, and the phase 2 fluxes when DBGPHI(R2) is T. The pressure-correction equation coefficients are printed at the time of their construction, provided DBGPHI(P1) is T.

### DBEDGE

---- PIL logical; default=F; group 25 --- -

DBEDGE....is subordinate to DBCOMP, DBGPHI(U1) and DBGPHI(V1). It ensures that in DBCOMP print-out, the edge values of v and u are printed, ie. v at IY=NY and u at IX=NX (for XCYCLE=F).

### DBEGWF

---- PIL logical; default=F; group 25 --- -

DBEGWF....gives print-out from the EGWF (EARTH Generated Wall Function) coding on a cell by cell basis.

### DBEMU

----- PIL logical; default=F; group 25 --- -

DBEMU....gives print-out of the kinematic viscosity (laminar and turbulent) when they are GROUND-set. A parameter MULT is printed which indicates by value 0 that the viscosities printed pertain to the current slab IZ; the value 1 signifies that the viscosities at IZ+1 are printed.

### DBEXP

----- PIL logical; default=F; group 25 --- -

DBEXP....gives information about the expansion/contraction of the grid at each time step, when ZMOVE is T.

### DBFLUX

---- PIL logical; default=F; group 25 --- -

DBFLUX....gives print-out of the cell-wise continuity errors at the stage in the calculation that the cell-face mass fluxes are calculated, provided that DBGPHI(P1) or DBGPHI(R1) or DBGPHI(R2) is set T. See also DBCONV.

### DBGAM

----- PIL logical; default=F; group 25 --- -

DBGAM....gives print-out of the exchange coefficients (the gammas) for those phis for which DBGPHI are T. See DBEMU for significance of MULT; MULT=-1 signifies printed gammas are those of IZ-1.

### DBGEOM

---- PIL logical; default=F; group 25 --- -

DBGEOM....governs debug print-out of the geometrical calculations. There are two parts to this output: the once-and-for-all work at the start of the calculation, and the calculations of areas and internodal distances performed at the start of each z slab. When DBINDX=T as well, the XFRAC, YFRAC, ZFRAC and TFRAC data are printed.

### DBGMAG

---- PIL logical; default=F; group 25 --- -

DBGMAG.... when set true, debug information is displayed on the VDU whilst MAGIC(L) is in use.

### DBGPHI

---- PIL logical array; default= F; group -

DBGPHI....is used to indicate for which dependent variables (DV) debug is wanted, eg. DBGPHI(W1)=T. The type of debug required for the DV indicated is specified by other debug parameters namely: DBCOMP, DBCMPE, DBCMPN, DBCMPH, DBSODA, DBGAM, DBFLUX, DBCONV and DBADJS for which help entries are provided.

If none of these other parameters is set, the DBGPHI(phi)=T elicits print-out of the residuals and solution of phi at the iteration(s), slab(s), sweep(s) and time step(s) indicated by the settings of ITHDB1 to ITHDB2, IZDB1 to IZDB2, ISWDB1 to ISWDB2, and ISTDB1 to ISTDB2.

### DBGRND

---- PIL logical; default=F; group 25 --- -

DBGRND....flags all entries to, and returns from, GROUND, within the bounds prescribed by IZDB1 etc. See also IDBGRD.

### DBINDX

---- PIL logical; default=F; group 25 --- -

DBINDX....gives print-out of the F-array segment addresses of all arrayed quantities in use in EARTH. It may be used to identify the address of an array for which it is desired to perform a SEARCH.

### DBL

------- PIL logical; default=F; group 25 --- -

DBL....gives print-out of the length scales (EL1 and/or EL2) when they are GROUND-set. See also DBEMU.

### DBMAIN

---- PIL logical; default=F; group 25 --- -

DBMAIN....elicits print-out from the subroutine which contains the iteration-, slab-, sweep- and time-step-DO loops. The print-out of the fluid mass in the each control cell is also controlled by this parameter. Used in conjunction with DBGPHI, DBMAIN gives print-out of the initial fields at start up.

### DBMDOT

---- PIL logical; default=F; group 25 --- -

DBMDOT....gives print-out of the inter-phase mass flux.

### DBONLY

---- PIL logical; default=F; group 25 --- -

DBONLY....gives print-out from subroutine ONLYIF.

### DBOUT

----- PIL logical; default=F; group 25 --- -

DBOUT....gives print-out details of the entry to and exit from the general field print-out subroutine.

### DBPRBL

---- PIL logical; default=F; group 25 --- -

DBPRBL....controls print-out of important parameters for parabolic calculations, such as the pressure level downstream of the current slab.

### DBRHO

----- PIL logical; default=F; group 25 --- -

DBRHO....gives print-out of the densities (RHO1 and/or RHO2) when they are GROUND-set. See also DBEMU.

### DBSHFT

---- PIL logical; default=F; group 25 --- -

DBSHFT....gives print-out from subroutines responsible for shifting field stores in and out of core when disc storage is in use. It also gives print-out relating to the reading and writing of the previous-time-step fields.

### DBSODA

---- PIL logical; default=F; group 25 --- -

DBSODA....gives print-out of SOurce DAta inputs specified by COVAL, for both linear sources and arrays of coefficients and values set in GROUND. This information is printed for those phis for which DBGPHI(phi) is set T, and for the patch number indicated by IREGDB.

### DBSOL1

---- PIL logical; default=F; group 25 --- -

DBSOL1....controls print-out from the one-dimensional linear equation solver, subject to DBGPHI.

### DBSOL2

---- PIL logical; default=F; group 25 --- -

DBSOL2....controls print-out from the two-dimensional linear equation solver, subject to DBGPHI.

### DBSOL3

---- PIL logical; default=F; group 25 --- -

DBSOL3....controls print-out from the three-dimensional linear equation solver, subject to DBGPHI. For a print-out over the entire field, IZDB2 and IZPRL (in Group 23) must be set to NZ.

### DBT

------- PIL logical; default=F; group 25 --- -

DBT....gives print-out of the temperatures (TMP1 and/or TMP2) when they are GROUND-set. See also DBEMU.

### DCOM

DCOM....This command causes the Satellite program to write its contents to COPYQ1 in addition to executing the line.

For example, DCOM(BFC=T) writes BFC=T into COPYQ1 and sets BFC to be TRUE.

(see REGEXT)

### Define Blocked Regions

This option defines blocked regions for the plot, in which no contours or vectors will be plotted.

A sub-menu will be activated for the extent of each blocked region in the X,Y and Z directions. Up to 10 blocked regions may be specified.

### Define Domain

-------------------- Define Do Photon Help ----

[Define Domain] activates the sub-menu for the extent of the domain in Cartesian coordinates.

It is used when PHOTON is run without PHI or XYZ files attached, in order to develop geometry files. The default domain extent is 0.0-1.0 in X,Y and Z.

### DEL

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

[Del] activates the menu for deleting a plotted element(s).

### DELAY

------ Command -----------------------

This command takes one integer argument,the value will be used to hold the program for a period of time. The greater the value is, the longer the program holds.

### Delete

[Delete] activates the menu for deleting existing TEXT element(s).

### DELETE

PHOTON will prompt for the first and the last GEOMETRY elements to be deleted. Action will only be taken if you press [Confirm].

### Delete

(Setup Block Region)------------------------------------- Photon Help ----

[Delete] the last block region.

### Delete all

(Grid, Contour, Vector, Stream, Surface Menu)--------------------------------- Photon Help ----

[Delete all] clears the current stack. For example, if the delete-menu is called from the vector-menu, [Delete all] deletes all the VECTOR elements previously generated.

### Delete last

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

[Delete last] deletes the last plotting element in the current stack. For example, in the VECTOR menu, [Delete last] will cause the most recently plotted VECTOR element to be deleted.

### DEN1

------ PIL integer name; default=0; group 7 -

DEN1....indicates which whole-field store will be used for the density of phase 1 in response to the command STORE(RHO1). Such storage is necessary when it is desired to under-relax this property. Once stored, this field should be initialized in group 11.

### DEN2

------ PIL integer name; default=0; group 7 -

DEN2.... indicates which whole-field store will be used for the density of phase 2 in response to the command STORE(RHO2). Such storage is necessary when it is desired to under-relax this property. Once stored, this field should be initialized in group 11.

### DENPCO

---- PIL logical; default=F; group 8 ----

DENPCO...., when T, causes the upwind densities to appear as multipliers in the pressure-correction coefficients; this may promote convergence when steep gradients of density are present.

A further consequence is that the printed residuals of the pressure equation have the dimensions of mass per unit time rather than volume per unit time.

Since June 2011, DENPCO is set T automatically by EARTH, whenever non-uniform densities are present.

### Density of first phase

(see RHO1 real, Group 9)

### Density of first phase, formulae for

(see RHO1 real, Group 9)

### Density of second phase

(see RHO2 real, Group 9)

### Density of second phase, formulae for

(see RHO2 real, Group 9)

### Density pressure correction

(see DENPCO logical, Group 8)

### Density, calculation of

(see RHO1,2, Group 9)

### Density, indication of in phase 1

(see DEN1 integer name, Group 7)

### Density, indication of in phase 2

(see DEN2 integer name, Group 7)

### DENST1

Integer used in GXDENS to denote first-phase density.

### DENST2

Integer used in GXDENS to denote second-phase density.

### Dependent variables, default values of

PHOENICS solves its differential equations by iterative guess-and-correct procedures. Therefore its dependent-variable arrays have to be filled with not-unreasonable values at the start; and this is handled automatically by the provision of "default" values, usually 1.E-10.

In a steady-flow problem, the initial guesses have no influence on the final solution. Often therefore PHOENICS users pay no attention to the initial values, being content to accept the default values.

### Dependent variables, setting PATCH-wise sources of

(see COVAL command, Group 13)

PHOENICS describes a phenomenon involving the flow of momentum, heat or material in terms of distributions in space and time of temperatures, velocities, pressures, concentrations and other physically meaningful quantities. These are the so-called dependent variables.

The distributions involve ascribing numerical values to the temperatures, velocities, etc. at each of an orderly array of locations, called 'nodes' or 'grid-points'; and, if the process is a time-dependent one, such distributions are calculated for each of a succession of instants of time.

PHOENICS can handle either one or two inter-penetrating "phases", i.e. distinguishable fluids. The flow of air alone is a single- phase flow; so is that of water alone. When however a bubbly mixture of air and water is in question, or that of air mixed with droplets of water, the flow is said to be a two-phase one; and the air and water are called phases.

EARTH is equipped to solve for up to 150 dependent variables, and as many more as you care to specify. Certain of the dependent variables can be referred to by name. These are:-
 Name Variable P1 the (shared) pressure of both the phases; U1 the x-direction velocity of the first phase; U2 the x-direction velocity of the second phase; V1 the y-direction velocity of the first phase; V2 the y-direction velocity of the second phase; W1 the z-direction velocity of the first phase; W2 the z-direction velocity of the second phase; R1 the volume fraction of the first phase; R2 the volume fraction of the second phase; RS the volume fraction of the 'shadow' of the second phase; KE the turbulence kinetic energy of one of the phases (the first phase by default); EP the rate of dissipation of turbulence kinetic energy for the same phase; H1 the specific enthalpy of the first phase; H2 the specific enthalpy of the second phase; C1 concentration variable for the first phase; C2 concentration variable for the second phase; C3 another concentration variable for the first phase; C4 another concentration variable of the second phase; .... ...... and so on, until C35 another concentration variable for the first phase.

However, variables C1 to C35 need not be concentrations; you can decide for yourself what they shall represent.

### Depth

Cells are filled using the Warnock method: each cell is subdivided until:

i) a subdivision can be filled with one colour
ii) the size of the subdivision is smaller than the pixel size
iii) the cell has been subdivided a specified number of times.
This is the parameter DEPTH.
Suggested values of DEPTH range from 1 to 8.

1 --- fills each cell with one polygon.
8 --- fills each cell to pixel level.

### Depth

The top view of the outline of the object is shown in the colour red and can be moved with the mouse relative to the centre of the screen, which defines the position of the object relative to the view plane.

The red cross at the centre of the screen shows the current centre for rotating and spinning.

### Desktop

The area of the Commander from which the PHOENICS modules can be run by using a hotkey or icon.

### DFEG

(Data Finite Element Generation) directive (see TR206)

### DIAGnostic

---------------------------------

Diagnostic messages are printed on occasion by the SATELLITE and by EARTH. Those from the SATELLITE will normally be concerned with errors in PIL syntax, and will indicate to the VDU (except in batch-mode output) the PIL statement in error. See group 25 and DEBUG to learn of what debug can be obtained from EARTH.

### DIFCUT

---- PIL real; default= 0.5; group 8 --- -

DIFCUT....diffusion/convection cutoff.

The diffusion contribution to the finite-volume-equation coefficient is diminished by DIFCUT*ABS(convection contribution), but not allowed to become negative, in order to account approximately for diffusion-convection interactions.

Therefore the default value, which cuts off diffusion when the cell Peclet number equals 2.0, corresponds to the "hybrid- interpolation" scheme, whereas DIFCUT=0.0, giving no diminution, corresponds to the "upwind-interpolation" scheme.

### Diffuser object

In the parlance of heating and ventilating engineers, a "diffuser" as a fitting through which air enters a room.

To facilitate their introduction into simulation scenario, special 'PHOENICS objects' are provided. Click here for the description in the FLAIR user guide.

(see GROUP 12)

### Diffusion fluxes, accessing or altering

(see UDIFF logical, Group 8)

### Diffusion neighbours,accessing or altering

(see UDIFNE logical, Group 8)

### Diffusion/convection cutoff

(see DIFCUT real, Group 8)

### DIGITISE

---- Autoplot Help ----

DIG[ITISE]

The cursor can be used to obtain the x and y coordinates of any series of points on the screen. These will be stored in memory as the next data set, and can thus be plotted as normal. The points can be saved on a disc file by using the ELEMENT SAVE command.

### DIMENSion

----------------------------------

>> See the Encyclopaedia entry 'DIMENSIONING'.

### DIMENSIONING

All the main PHOENICS arrays are dimensioned dynamically at runtime. For more details see the entry Dynamic storage

### Direct-access file

A type of data file used by PHOENICS in which the information is accessed directly, rather than sequentially (see sequential formatted file). Direct-access files are quicker to access than sequential files, but they are not portable across machines of different makes.

### Direction

The surface contour will be generated by going through all the planes along the direction; it can be X, Y or Z.

### DISPLAY

When the word DISPLAY starts in the third column of a Q1 file, all of the lines following it are displayed on the screen, until the command ENDDIS, also starting in the third column, is encountered,

Library case 701 shows an example, and illustrates the placing of the DISPLAY text between

#cls,

which clears the screen and

#pause

which prevents further scrolling until RETURN is pressed.

Library case 492 shows that it is also possible to place

#pause

statements within a DISPLAY section. This is necessary if there are too many lines of text to be seen at any one time.

Valid PIL statements within a DISPLAY section, if they start in the first or second column, will be executed, but not printed. However it is recommended that they should not be placed there, for the sake of orderliness.

When the VR-Editor is being run, the DISPLAY appears in the text window in the bottom right-hand corner of the screen. The display of the text window is controlled by the View - Text box menu. The #pause macro will cause the text window to appear automatically if it had been turned off.

Additionally, when the cham.ini file contains the line:

display=on

the presence of DISPLAY in the Q1 file causes SATELLITE to:

• copy the material in question into a file called display.htm,
• activate the default browser, and
• display the contents of the file on the screen.

This is especially useful when the DISPLAY section contains HTML links, as does, for example, that of library case h101 .

### DISTIL

---- PIL logical; default=F; group 20 --- -

DISTIL....when set T directs to logical unit 21 a "distilled" output. This highly compressed print-out is used when the code is installed, in order to check that the test battery is working correctly. For each variable stored, it prints out an EXpected mean value and the calculated mean value, and if these two numbers differ by more than a pre-set tolerance a CHECK flag is printed.

See DSTTOL, NULLPR and EX for further information.

### Distilled output

(see DISTIL logical, Group 20)

### DISWAL

------------- Command; group 9 ------------ DISWAL

DISWAL... activates the calculation of the distance of the centre of each cell from the nearest wall, and is equivalent to the following PIL commands;

SOLVE(LTLS);SOLUTN(LTLS,Y,Y,Y,P,P,Y)
TERMS(LTLS,N,N,Y,N,Y,Y)
STORE(WDIS);LITER(LTLS)=1000

The wall distance is used by the LVEL turbulence model and the IMMERSOL radiation model.

### DIVIDE /DIVIDE X /DIVIDE Y

---- Autoplot Help ----

DI[VIDE] [X or Y] [a] [i] [j]

Divide x- or y- coordinates of data elements i - j by amount a. Amount and element range will be prompted for. At any stage '/' forces return to OPTION?. See also HELP on : MULTIPLY X, MULTIPLY Y, SHIFT X, SHIFT Y

### (1) DO loops are implemented in PIL by the commands:

DO <DO loop counter>=<low value>,<high value>,[<increment>]
<pil statements>
ENDDO

<DO loop counter> is a name to which the value of the DO loop counter is assigned. Within the scope of a DO-loop, the <DO loop counter> can be accessed like any other Integer variable. The <DO loop counter> must not have been defined previously as a PIL variable.

<low value> and <high value> define the range over which the <DO loop counter> runs; they are Integer expressions.

<increment> is the optionally-specified increment to the <DO loop counter> and is an integer expression which can be positive or negative. If it is not specified, it defaults to 1.

ENDDO denotes the end of the DO-loop. For example, for NX=2, NY=8 and NZ=12, the following DO loops are valid and execute 6 times:

DO II=1,6
DO II=NY,NX,-1
DO II=NX+NY,2*NZ-2,2
...
...
...
ENDDO
ENDDO
ENDDO

DO loops can be nested to a maximum depth of 20. The FORTRAN-77 convention for 'zero-trip' loops has been followed. Thus, for example:

DO II=2,1 .... ENDDO

will not be executed at all.

### (a) The following statements:

DO JJ=1,3
+ PATCH(INL:JJ:,NORTH,1,1,JJ,JJ,1,1,1,1)
ENDDO

are equivalent to:

PATCH(INL1,NORTH,1,1,1,1,1,1,1,1)
PATCH(INL2,NORTH,1,1,2,2,1,1,1,1)
PATCH(INL3,NORTH,1,1,3,3,1,1,1,1)

### (b) The following command sequence

sets the inflow at the IY=NY boundary of a POLAR case, over the first section of the circumference, and puts a fixed pressure over the remainder.
```

GROUP 13. Boundary conditions and special sources
Inlet
REAL(UEXT,UIN,VIN,ANGU,ANGV)
INTEGER(IM1)
UEXT=1.0
DO II=1,IX1
+ ANGU=XULAST*XFRAC(II);UIN=UEXT*SIN(ANGU)
+ IF(II.EQ.1)THEN
+   ANGV=.5*XFRAC(II)*XULAST
+ ELSE + IM1=II-1
+   ANGV=ANGU-.5*(XFRAC(II)-XFRAC(IM1))*XULAST
+ ENDIF
+ VIN=UEXT*COS(ANGV)
+ INLET(IN:II:,NORTH,II,II,NY,NY,1,1,1,1)
+ VALUE(IN:II:,P1,VIN*RHO1)
+ VALUE(IN:II:,U1,UIN)
+ VALUE(IN:II:,V1,-VIN)
ENDDO
```

### DMPSTK

---------- PIL logical, default T -------

The default setting ensures that on exit from the SATELLITE, Q1 is overwritten by the contents of the stack, and not COPYQ1 as was the case in PHOENICS V1.4. This means that any DO loop and other flow-control constructs will be preserved.

When set to F, Q1 will be overwritten with COPYQ1, which contains the 'processed' PIL which results from the execution of the stack.

### DO

---------------- Advanced PIL command --- -

DO loops may be included in Q1 files. The syntax is exemplified by:

DO II=1,NX+1
XC(II,1,1)=II-1
ENDDO

### Do

[Do] takes the current setting and draws the plotting element on the screen.

### DO

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

DO <var>= <start value> <end value> <inc value>

<PHOTON commands>

ENDDO

The DO command enables a series of PHOTON commands to be repeated over a range of values. The syntax is similar to a DO loop in FORTRAN, however there is no label nor it is possible as yet to do nested DO loops. It is available under both command mode and use files. As in FORTRAN the increment value is optional.

For example to plot vectors over each of the Z planes:
DO IZ = 1 M
VEC Z IZ SH
ENDDO

When plotting contours it is necessary to provide additional values, eg a sub-division size with the fill option. These must be supplied on the same record otherwise the DO loop will fail. So that:
DO IX = 1 M 5
CON TEM1 X IX FILL ; 0.01
ENDDO

will provide colour fill contours, but
DO IX = 1 M 5
CON TEM1 X IX FILL
0.01
ENDDO

will cause an error. However, if the subdivision size is ommitted then the user will be prompted for it when the line is processed.

### Dollar-name patches

If a PATCH name begins \$name, where name is the four-character name of a solved or stored variable, a corresponding COVAL for variable PHI will introduce a source of PHI equal to:

(VAL-PHI)*CO*NAME

where CO is the third argument of the COVAL, VAL is the fourth argument of the COVAL, and NAME stands for the local value of the variable having the name which has been referred to.

### DOMAIN

---- Command; group 6 ---------------

DOMAIN....is a 6-argument command used for the specification of sub-domains for the purpose of generating a body-fitted grid. The 6 arguments are for integers Ifirst to Ilast, Jfirst to Jlast and Kfirst to Klast, in the corner-coordinate nomenclature described under the BODY-F entry.

Typically, DOMAIN is used to define lines, areas (enclosed by 4 lines) and volumes (enclosed by 6 areas). A DOMAIN command should always be followed by commands which fill in the grid coordinates within the sub-domain defined. For example, the following commands will cause one edge of the domain to fall on a straight line the end points of which are the cartesian coordinates 1.0,1.0,1.0 and 10.0,10.0,10.0 :

```
SETPT(1,1,1,1.,1.,1.); SETPT(1,1,NZ+1,10.,10.,10.)
DOMAIN(1,1,1,1,1,NZ+1)
SETLIN(XC,XF+(XL-XF)*LNK)
SETLIN(YC,YF+(YL-YF)*LNK)
SETLIN(ZC,ZF+(ZL-ZF)*LNK)
```

The SETPT commands set the cartesian coordinates of the end points of the line defined by DOMAIN; and the SETLIN commands set the cartesian coordinates of the cell corners on this line to vary linearly with the K index from one end to the other. Here, LNK signifies "linear in K", ie. it equals (K-KF)/(KL-KF).

See SETPT and SETLIN for further information.

### DOMAIN

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

DO[main].... prompts for the extent of the domain in Cartesian coordinates. It is used when PHOTON is run without PHI or XYZ files attached, in order to develop geometry files. The default domain extent is 0.0-1.0 in X,Y and Z.

### DONACC,the donor-acceptor method

DONACC is defaulted to F. It is active only for transient, two- phase calculations; that is for STEADY=F and for ONEPHS=F. Under these circumstances, DONACC=T selects the so-called 'donor- acceptor' scheme for formulating the volume fraction (R1 and R2) equations.

The DONACC=T setting is appropriate for calculations in which the two phases are separated by a distinct, continuous interface, as, for example, when the motion of a wave on a liquid surface, or that of a large gas bubble in a body of liquid, is to be considered. The alternative two-phase situation (for which DONACC should remain =F) occurs when the two phases are finely dispersed, at least as compared with the grid size; examples are the steam-water mixture, and finely-distributed fuel particles or droplets which are suspended in the gases within a furnace or combustion chamber.

The job of DONACC is to ensure the maintenance of the sharpness of the interface as it moves about in time. Thus, DONACC=T involves special interpolation rules for determining the volume fraction used in the calculation of cell-face mass fluxes.

For DONACC=T, RLOLIM sets the value of the phase-1 volume fraction (ie R1) below which each cell is regarded as full of phase-2 fluid. The value of R1 above which the cell is regarded as full of phase-1 fluid is RUPLIM. A suitable value for RLOLIM is of the order of 0.001 to 0.01.

Flows exhibiting a sharp interface may also be treated as single- phase flows with discontinuities of properties. See GALA, and HOL.

(see DONACC)

### Dongle

A hardware device which is used sometimes for locking PHOENICS to a machine.

### DOS

(Disk Operating System) Operating system used by PC's.

### DOT

---- Autoplot Help ----

DO[T]n [i] [j]

Plots data elements i - j using dashed lines of type n. If i & j are omitted all elements in memory but not on the screen will be plotted. 'n' is an integer in the range 1 - 5 as follows :
 DOT1 = short dash; DOT2 = dash-dot; DOT3 = medium dash; DOT4 = long dash; DOT5 = very long dash.

If n is omitted, DOT1 is assumed.

### Dot-patch, a new (April 2009) PIL command

• A Dot-patch is a PATCH, of the kind used in a Q1 file for setting initial and boundary conditions, which has a dot as the first character of its name, e.g.
.STEP

• The 'dot-patch' command is similar to the conventional PATCH command; but the position of the corresponding patch in four-dimensional space-time is not represented by the conventional indicial arguments: IXF, IXL, IYF, IYL, IZF, IZL, ITF, ITL.

• Instead, the place of these arguments is taken by corresponding real numbers: RXF, RXL, RYF, RYL, RZF, RZL, RTF and RTL.
These represent the lowest and highest coordinates of the 'faces' of the 'space-time block' in the x, y, z and time directions, normalised by reference to the domain extents, namely XULAST, YVLAST, ZWLAST and TLAST.

• The dot at the start of the name is a signal to the EARTH module that the indices corresponding to the first and last grid interval must be evaluated from the above eight arguments and from the separately-defined computational grid.
Its advantage is that the user does not have to consider what grid is to be used.

• An Input-File-Library case illustrating the use of a dot-patch is case 289, which concerns the influence of grid fineness on the flow over a backward-facing step.

• When first introduced (April, 2009), the dot-patch had three limitations, namely:
1. The RXF, RXL, etc had to be given 1000 times their proper values, so as to circumvent the proclivity of the SATELLITE to turn them into whole numbers.
EARTH subsequently divided them by 1000 in order to compensate.
2. Because it as yet had not been instructed to do so, the SATELLITE, took no account of dot-patches when adjusting the grid to fit objects or 'regions'; this would be desirable as an option.
3. RTF could not be given the value 0. as would be natural for inital value patches or for boundary-condition patches which are active from the start of the simulation time, because it interfered with the SATELLITE's indexing arrangements. 1.0 had to be used instead.
All these limitations have since been removed.

### Downstream pressure for parabolic calculations

(see PBAR & AZPH)

### Downward

(Stream Set Menu)----------------------------------- Photon Help ----

Streamlines will only be tracked downstream from the starting positions.

### DRAG_LIFT, a PHOENICS-VR object type

A DRAG_LIFT object is used to define a region over which the momentum imbalance (force) will be calculated. See the description in the PHOENICS_VR Reference Guide, TR326

### DRAW

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

DR[aw] .... is a REPLAY command which displays a frame from a SAVE file. The FILE command must have been used to open a SAVE file before DRAW can be used.

The SCALE and SHIFT commands can be used to alter the size and position of the frame on the screen, and the CLEAR/NOCLEAR commands permit the building up of pictures from separate frames.

### DRAW

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

[Draw] activates the sub-menu for drawing individual an plotting element (e.g. Grid, Vector etc.).

### DRAW

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

[Draw] displays a frame from a SAVE file. The SAVE file must have been opened with FILE first.

[Scale] and [Shift] can be used to alter the size and position of the frame on the screen, and the [Clear/NoClear] commands permit the building up of pictures from separate frames.

### Draw

[Draw] causes the streamlines to be drawn according to the current setting.

### Draw

[Draw] causes a SURFACE to be drawn according to the current setting.

### DRH1DP

---- PIL real; default= 0.0; group 9, .. -

DRH1DP....is the compressibility of the phase 1 fluid equal to, (d(RHO1)/dp)/RHO1 ,ie. d(ln(RHO1))/dp .

Its value is stored three-dimensionally, and may therefore be printed out, under-relaxed, or held between the VARMIN and VARMAX limits, by including the command:
STORE(DRH1)
in the Q1 file.

Non-uniform values of DRH1DP may, in PHOENICS versions later than 3.3, be conveniently set by way of In-Form; but setting via GROUND remains possible, as follows.

If DRH1DP is given a positive value, that value is used for the dependence of the first-phase density on pressure. Recourse to GROUND is necessary when density is a non-linear function of pressure, or a function of other variables. The following options have been provided in subroutine GXDRDP called from GREX, and are selected as indicated:

DRH1DP=GRND3 selects the compressibility formula that results when the RHO1=GRND3 density option is differentiated with respect to pressure and divided by density, ie. RHO1B/(pressure+PRESS0). As a safety precaution, GREX automatically sets DRH1DP=GRND3 if it finds that RHO1=GRND3.

DRH1DP=GRND5 associates an isentropic formula with the RHO1=GRND5 option ( which has the ideal-gas-law form ), ie. it sets DRH1DP to, RHO1C/(pressure+PRESS0), where RHO1C is the ratio of the specific heat at constant volume to the specific heat at constant pressure. As a safety precaution, GREX sets DRH1DP=GRND5 if it finds that RHO1=GRND5; and if RHO1C is zero ( i.e. not set ), then RHO1C is set to 1.0/1.4.

If these options fail to meet the user's needs, he should set DRH1DP=GRND and insert the appropriate coding sequence in subroutine GROUND, GROUP 9 SECTION 2, using the index D1DP to set the in-EARTH storage array for this quantity at the current slab.

The built-in enthalpy source term that represents the work done by the pressure ( ie. the substantive derivative Dp/Dt - see SOURCE) is omitted by EARTH if it finds that DRH1DP is zero ( ie. that the fluid is incompressible ), irrespective of the second argument of TERMS for H1.

### DRH2DP

---- PIL real; default= 0.0; group 9, .. -

DRH2DP....is the compressibility of the phase-2 fluid equal to, (d(RHO2)/dp)/RHO2 ,ie. d(ln(RHO2))/dp . It is used similarly to DRH1DP of which the entry should be consulted for further information.

Placing a STORE(DRH2) command in the Q1, causes it to become a whole-field variable.

### DSTTOL

---- PIL real; default= 1.E-2; group 20 - -

DSTTOL....is the tolerance which determines the magnitude of the disparity between the EXpected and calculated values at which a 'CHECK' flag is printed in the distilled output.

See DISTIL for further information.

### DT

DT is a Fortran real variable used in GROUND. It represents the current time-step size.

### DTFALS

----- PIL real array --------------------

Internal storage of information set by RELAX command.

### DUDX

------ PIL logical; default=F; group 19 --- -

DUDX....= T causes the inclusion of the du/dx term in the generation function used in the source of KE and as the dissipation source in the specific enthalpy equation, H1.

The user can activate the inclusion of those other spatial derivatives of velocity that he regards as significant by setting DUDY, DUDZ, DVDX, DVDY, DVDZ, DWDX, DWDY and DWDZ as required. By setting GENK=T the user can activate all terms. In BFC cases, the full generation term is computed, and DUDX etc. are not used.

### DUDY

------ PIL logical; default=F; group 19 --- -

DUDY.....See DUDX.

### DUDZ

------ PIL logical; default=F; group 19 --- -

DUDZ.....See DUDX.

### DVDX

------ PIL logical; default=F; group 19 --- -

DVDX.....See DUDX.

### DVDY

------ PIL logical; default=F; group 19 --- -

DVDY.....See DUDX.

### DVDZ

------ PIL logical; default=F; group 19 --- -

DVDZ.....See DUDX.

### DVO1DT

---- PIL real; default= 0.0; group 9, .. -

DVO1DT....is the volumetric coefficient of thermal expansion of the phase-1 material, i.e. it is the proportional change in specific volume of that material which is brought about by a one-degree increase in temperature.

It is useful for the prediction of natural-convection heat transfer, and for the calculation of thermal stresses in solids.

Its value is stored three-dimensionally, and may therefore be printed out, under-relaxed, or held between the VARMIN and VARMAX limits, by including the command:
STORE(DVO1)
in the Q1 file.

Non-uniform values of DVO1DT may, in PHOENICS versions later than 3.3, be conveniently set by way of In-Form; but setting via GROUND, or activation of gxthrmx.for remains possible.

Use of the last of these methods requires DVO1DT to be set to GRNDx, where x denotes the option chosen; then the variables DVO1A, DVO1B must be given appropriate values. The built-in formulae are as follows (where the absolute temperature, Tabs, is equal to the local temperature, TEM1 or TMP1, plus the constant, TEMP0, which is set in the Q1 file; H1 is the enthalpy):

• DVO1DT = GRND1 selects:
DVO1DT = DVO1A (constant)

• DVO1DT = GRND2 selects:
DVO1DT = DVO1A + DVO1B*Tabs + DVO1C*Tabs**2 (quadratic function of temperature)

• DVO1DT = GRND3 selects:
DVO1DT = DVO1A + DVO1B*H1 + DVO1C*H1**2 (quadratic function of enthalpy)

• DVO1DT = GRND4 selects:
DVO1DT = DVO1A + CP1B*Tabs (linear function of temperature)

• DVO1DT = GRND5 selects:
DVO1DT = a function of temperature interpolated from tabulated values, defined in gxthrmx.for.

### DVO2DT

---- PIL real; default= 0.0; group 9, .. -

DVO2DT....is the volumetric coefficient of thermal expansion of the phase-2 material. Mutatis mutandis, remarks about DVO1DT apply to it also.

### DWDX

------ PIL logical; default=F; group 19 --- -

DWDX.....See DUDX.

### DWDY

------ PIL logical; default=F; group 19 --- -

DWDY.....See DUDX. For the significance of DWDY=T and NONORT=T, see DWDX.

### DWDZ

------ PIL logical; default=F; group 19 --- -

DWDZ.....See DUDX.

### DXG2D

DXDG2D is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of: distances in the IX-direction between centres of continuity cells. In polar coordinates (CARTES=F) where the IX-direction changes continuously with increasing angle, the distance between neighboring cell centres is equal to the chord length, ie. (RINNER+0.5(YFRAC(IY)+AMAX1(0.0,YFRAC(IY-1)))) * 2.0*SIN((XFRAC(IX+1)-AMAX1(0.0,XFRAC(IX-1)))/4.0)*XULAST) .

Note that this index is present only if CALL MAKE(DXG2D) is present in Group 1, Section 1 of GROUND.

### DXU2D

DXU2D is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of: distances in the IX-direction between walls of continuity cells, where the u velocity resolutes are stored.

### DYG2D

DYG2D is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of:

Note that this index is present only if CALL MAKE(DYG2D) is present in Group 1, Section 1 of GROUND.

### DYV2D

DYV2D is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of: distances in the IY-direction between walls of continuity cells, where the v velocity resolutes are stored.

Note that this index is present only if CALL MAKE(DYV2D) is present in Group 1, Section 1 of GROUND.

### DZ

DZ is a Fortran real variable, usable in In-Form statements or in GROUND coding. It represents the current z-direction thickness of the current slab of cells; or else the forward-step size in parabolic calculations.

### DZG

DZG is a Fortran real variable, usable in In-Form statements or in GROUND coding. It represents the distance between the cell centres of the current-slab cell and the high-slab cell.

### DZGL

DZGL is a Fortran real variable, usable in GROUND coding. It represents the DZG of the low-slab cell.

### DZGNZ

DZGNZ is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of: the distances in the IZ direction between centres of continuity cells. The array is accessed via GETZ and holds values for all IZ. When BFC=T, use GTIZYX with the index DZGPH (28); see the SUBROUtine entry for information on GTIZYX and GETZ.

### DZL

is a Fortran real variable, usable in GROUND. It represents the z-thickness of the previous slab.

### DZRAT

DZRAT is a Fortran real variable, usable in GROUND. It represents DZ / DZL.

### DZW1

------ PIL real; default=0.0; group 5

DZW1 is the factor in the equation DZ = DZW1 * grid_width,
used for parabolic flows, when AZDZ has been set to:

• PROPX, a synonym for GRND1.
Then grid_width is the local value of XULAST.

• PROPY, a synonym for GRND2.
Then grid_width is the local value of YVLAST.

### DZWNZ

DZWNZ is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of: values for the distances in the IZ direction between walls of continuity cells. The array is accessed via GETZ and holds values for all IZ.