Encyclopaedia Index

P1 P2 PAGE PANEL PARAB PARABOLIC FLOWS Parallel PHOENICS Parallel solver PARDAT Parameterized Q1 files PARSOL Particle-tracking PATCH PATCH-WISE Variables PATGEO PAUSE
PBAR PBCL file PCB object PEA
PEOPLE object PERSON object PERSPVU

### P1

----------------------------------------- Integer flag; value=1.

P1....standard name used to denote first-phase pressure. P1 is also used to specify the first-phase mass-flow.

See PHI and NAME for further information.

### P2

----------------------------------------- Integer flag; value=2.

P2....standard name used to denote second-phase pressure or mass- flow. See PHI and NAME for further information.

STORE(P2) causes the pressure acting on the second phase in the momentum balance to be P1 + P2 (so P2 is the EXTRA pressure experienced by phase 2).

It is the responsibility of the user to provide coding which ascribes values to P2; but an example has been supplied in GREX3, group 19, where P2 is set proportional to R2. This is useful for the simulation of then floating layers, for example oil slicks.

### PAGE

---- Autoplot Help ----

PAG[E]
Produces plots which copy directly into a CHAM full-page report box. The default text size is size 4.

### PANEL

---- Autoplot Help ----

PAN[EL]
The plot will be redrawn in CHAM report panel format.

### PARAB

----- PIL logical; default=F; group 5 ----

PARAB.... when T , indicates that the flow is parabolic. Then the calculation is performed in only one sweep by a marching integration that proceeds from low z to high z, with LITHYD iterations performed at each forward z step.

The specification of the mean pressure level at each z location is governed by the parameters IPARAB and AZPH.

PARAB=T can also be used to solve for hyperbolic flows by means of a marching integration, thereby cutting out all influences from high-z to low-z.

See PHENC entry: parabolic flows.

### Parallel PHOENICS

PHOENICS can be operated on parallel-processor systems. The following documents provide relevant information.

### Parameterized Q1 files

These files are those which exploit the capabilities of the PHOENICS Input language to:
• declare new variables, whether real, integer, character or boolean i.e. logical;
• employ conditional structures (if....then....else);
• send messages to the monitor screen and invite responses via the keyboard.
They are discussed at length here; and tutorials which explain how to create and use them may be accessed by clicking here.

See also the Encyclopaedia entry on the protected mode of Satellite operation.

### PATGEO

PATGEO is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of:
geometrical information about the current patch. For example, if the current patch is of type EAST, PATGEO refers to the areas of the eastern cell faces over the current patch at the current z-slab.

### PATGEO: Automatic output of geometry for PHOTON

A GROUND add-on has been prepared that writes the geometrical information of all the PATCHes as PHOTON GRID OUTline commands in a PHOTON USE file. The file can then be executed from PHOTON to draw automatically the geometrical features of the problem by means of the command USE PATGEO, entered after the loading the PHI file.

### PAUSE

---- Autoplot Help ----

PAU[SE]

### PAUSE

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

PA[use]....suspends program execution until you press <Return>. This command is intended mainly for use in USE files.

### PBAR

------ PIL real; default= 0.0; group 14 -- -

PBAR....downstream mean pressure for use in parabolic calculations, i.e. PARAB=T. If IPARAB=0, as in confined flows, the downstream pressure at each z slab is computed by EARTH; but, if IPARAB>1, as in unconfined flows, the user must prescribe the downstream pressure via PBAR.

If the unconfined flow is one of zero pressure gradient, then PBAR may simply retain its default setting of 0.0. However, if a z-wise variation of pressure needs to be prescribed, then the user must set PBAR in the Q1 file to the required pressure level of the first slab, and then the downstream pressure at each z slab must be set via AZPH as explained under the entry AZPH.

In addition to prescribing the downstream pressure level, the user must also prescribe velocity boundary conditions at the free boundaries of the current forward step that are consistent with the prescribed variation of PBAR; thus, the pressure and the longitudinal velocity should obey the Bernoulli relation:

P + 0.5*rho*w**2/2 = constant.

For example, consider the case of a y-z boundary-layer calculation over a flat plate on the South boundary, and in which the North boundary is a free stream with an axial velocity which increases linearly with z. For this situation of a boundary layer in a favourable pressure-gradient the user would set the following PIL commands in the Q1 file:

 IPARAB > 1 which means that the downstream pressure PBAR must be prescribed by the user. AZPH = GRND which means that the downstream pressure PBAR must be set by the user in Group 14 of GROUND for each z slab. PBAR = 0.0 which defines the pressure level for the first z slab.

In Group 14 of GROUND the user would insert the following
coding to define the downstream pressure:

• GWFRE=ZW+GZ0
• PBAR=PTOT0-0.5*RHO1*GWFRE*GWFRE

where:

• GWFRE is the free-stream velocity;
• GZ0 is the user-specified virtual origin;
• ZW is the z-location of high face of the current z-slab;
• RHO1 is the fluid density; and
• PTOT0 is the user-specified free-stream total pressure.

The foregoing settings must be reinforced by appropriate free- stream boundary conditions at each z, thus in the Q1 file:

• PATCH(FREE,NORTH,1,1,NY,NY,1,NZ,1,1)
COVAL(FREE,P1,FIXP,0.0);COVAL(FREE,W1,ONLYMS,GRND)

The GRND value for W1 causes EARTH to visit Group 13 Section 12 of GROUND for a value for the cell at NY equal to the external velocity at the current IZ slab, as the following Fortran coding contrives:

IF(INDVAR.EQ.W1.AND.NPATCH(1:4).EQ.'FREE') THEN
L0VAL=L0F(VAL)
F(VAL+NY)=ZW+GZ0
ENDIF

See the Encyclopaedia entry 'VAL' for the significance of the VAL index.

### PBCL.DAT File

The pbcl.dat file is written by Earth to facilitate graphical display of the flows around and within objects of which the surfaces cut the computational grid planes obliquely, for which bodies PARSOL creates subsidiary cells, referred to as 'sub-cells'.

At the present time, cut cells can contain only two sub-cells, of which the one which lies outside the object is called 'sunny' and the one inside is called 'dark'.

PBCL is an acronym signifying 'Partially-Blocked Cell', which is what cut cells were called at first, when the sunny sub-cell was always filled with a fluid and the dark-sub-cell with a solid which 'blocked' the flow. This restriction no longer exists.

Pbcl.dat is read by the Viewer; and is also read by Earth itself when performing restart runs.

The structure of the file is as follows:

• line 1 contains:
• the total number of cut cells in all domains, NPBC,
• the PHOENICS version number (2 integers, format (I8, I3))
• The next three lines are then repeated for each cut cell.
• line 2 contains:
• the domain number;
• the structured-grid cell number within the domain, namely (IX-1)*NY+IY+(IZ-1)*NX*NY;
• the PRPS value of 'sunny' subcell(4 integers, format (I8));
• the PRPS value of the 'dark' subcell (4 integers, format (I8));
• line 3 contains 12 reals, format (1P12E13.6), namely:
• x,y,z coordinates of the cell-cutting face centre (3 reals);
• x,y,z components of unit normal to that surface (3 reals);
• x,y,z coordinates of the centre of the sunny subcell (3 reals);
• x,y,z coordinates of the centre of the dark subcell (3 reals);
• line 4 contains: M*2*number_of_cut_cells values of sunny and dark sub-cell PHI values
(M*2*NPBC reals, format(1P12E13.6))
where M is the number of STOREd variables.

If an attempt is made to restart an Earth run with PARSOL=T, but the pbcl file is absent or empty, Earth will issue an error message and stop. If it is desired under these circumstances to force the restart to continue, the line:

```    SPEDAT(SET,RESTRT,PARSOL,L,F)
```

can be added to group 19 of Q1. The Earth run will continue. All variables which would have been read from pbcl (i.e. have FIINIT(phi)=READFI) will have the fluid and solid values in the cut cells set to zero. Variables not set to be read from pbcl will have their fluid and solid values initialised normally. This setting can be made from the VR-Editor Main Menu 'Initialisation' panel by setting 'Restart cut-cell values' to NO.

When intermediate dumping (steady or transient) is activated, the names of the intermediate pbcl files are derived from pbc+ start_letter+sweep or step number. If the start letter is A and the dumping frequency is 1, the files will be pbca1, pbca2, pbca3 etc. For steady cases the start letter is always s.

If for some reason it is decided not to write intermediate pbcl files during a steady run, perhaps because the files are too big or too slow to write frequently, the setting

```    SPEDAT(SET,DUMP,PARSOL,L,F)
```

can be added to group 19 of Q1. Only the final pbcl at the end of the run (or end of each time step for which dumping is requested) will be written.

If the PHIDA flag is set to F, the PBCL file will be written as sequential formatted using the formats given above. If PHIDA=T, the PBCL file will be written as sequential, unformatted. This is the quickest to write and produces the smallest file sizes; but they are not human-readable.

### PCB, a PHOENICS-VR object type

A PCB object is a 3D volume, solid or fluid with non-isotropic thermal conductivity. See the description in the PHOENICS_VR Reference Guide, TR326

### PCOR

------ PIL integer name; group 7 ----------

PCOR.... indicates which whole-field store will be used for the pressure corrections in response to the command STORE(PCOR).

See IMB1 for further information.

### PEOPLE, a FLAIR object specifying the heat source due to a number of people

See the description in the FLAIR User Guide.

### PERSON, a FLAIR object specifying the heat source due to a single person

See the description in the FLAIR User Guide.

### PerspVU

PHOTON will generate the image in perspective view.

### Phase

(Vector Edit Menu)-------------------------------------- Photon Help ----

[Phase] permits selection of the plotting of first- or second-phase velocity vectors. Phase 1 is the default, and the second-phase vectors may be plotted by typing in 2. This menu button is inactive for single-phase runs.

(see EL1)

(see EL2)

(see PHNH1A)

(see CINH1A)

(see CINH2A)

### PHASEM

---- PIL real flag; value= 13.0; group 13 -

PHASEM....is a PATCH type used to dictate that the sources associated with the corresponding COVAL commands in group 13 will be equal to:

coefficient*(value - variable value at the grid node) *(mass of the relevant phase in the cell).

PHASEM is recommended for introducing gravitational and other body-force fields, in which case FIXFLU will normally appear in the coefficient location. It ensures that the mass calculated is consistent with the other terms in the finite-domain equation, especially the pressure term. One consequence of this is that no motion will be predicted for a fluid subjected to a uniform body force ( eg. as in hydrostatics ).

It is recommended for use when flow resistance resulting from fluid-solid interactions are to be represented by empirically-based pressure-drop correlations. It will ensure that the finite-domain formulae will reduce exactly to the required correlation ( when resistance is the dominant force ).

### PHENC

, the abbreviation used for PHOENICS Encyclopaedia

### PHNH1A

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

PHNH1A....parameter used in formulae for phase-1 interface values of dependent variables(phi). Further parameters of the same kind are PHNH1B and PHNH1C.

(see CONFIG)

### PHOENICS ENVIRONMENT

This module is nothing other than the VR-Editor; but the name 'environment' is used when it is desired to emphasise that buttons which appear on the Editor window can initiate many other actions than those associated with the input of simulation-defining data.

The environment module can be activated by the commands 'vre' or 'sat e'.

In some documents, for example TR 326, it is referred to as the 'VR-Environment'.

It may be truly said that the Satellite in 'environment' mode competes with the PHOENICS Commander; for their capabilities do overlap to some extent.

Since however this competition allows users to choose which they prefer, CHAM sees no reason to eliminate it.

(see PIL)

### PHOENICS-3

(see PHOENICS Overview, and PHOENICS Chronicle)

### PHS2P

----- PIL logical; group 19; sec. 4 ------

PHS2P... is used, for two-phase cases, to select the particular method used for calculating the pressure excess of the second phase.

See the help and encyclopaedia entries on P2, and GREX for further information.

### PHS2PA

---------- PIL real; group 19 -----------

PHS2PA... is used in the calculation of the pressure excess of the 2nd phase fluid when P2 is stored.

See the help and encyclopaedia entries on P2, and GREX for further information.

### PHS2PB

---------- PIL real; group 19 -----------

PHS2PB... is used in the calculation of the pressure excess of the 2nd phase fluid when P2 is stored.

See the help and encyclopaedia entries on P2, and GREX for further information.

### PHS2PC

---------- PIL real; group 19 -----------

PHS2PC... is used in the calculation of the pressure excess of the 2nd phase fluid when P2 is stored.

See the help and encyclopaedia entries on P2, and GREX for further information.

### PICKUP

---- PIL logical; default=F; group 11 --- -

PICKUP....start run N from run N-1. When set T in GROUP 11, the initial fields are those resulting from the previous run in a multi-run series. See RUN.

(see CONFIG)

### PINTO

PINTO is a stand-alone code which makes it possible to transfer phi-file and xyz-file data from one grid to another which is coarser or finer.

### Plane

(Contour Menu) ------------------------------------- Photon Help ----

[Plane] tells the plane where the current CONTOUR element is being plotted.

### Plane

(Contour Edit Menu) -------------------------------------- Photon Help ----

The colour scale for shaded and filled contours is determined by the maximum and minimum values of the plane on which the contour is being plotted. PLANE scaling is used to plot contours on a single plane where the range of values is narrow compared to the overall field range.

### Plane No.

[Plane No.] specifies the plane where the current GRID element is being plotted.

### Plane No.

[Plane No.] specifies the plane where the current VECTOR element is plotted.

### PlanNo

[PlanNo], together with X (or Y or Z), specifies the grid plane on which the plot is to be drawn. In the case of STREAMLINES, it specifies the particle seeding plane.

### PLANT

was introduced into PHOENICS in 1997 so as to enable the capabilities of PHOENICS to be extended by users in any desired direction. This they could of course already do by means of 'user-programming'; but PLANT does the programming for them.

PLANT allows users to express their wishes by way of formulae typed into the Q1 file; these are then converted automatically into their Fortran equivalents in a GROUND sub-routine, which is then compiled and built into a special executable.

While this is convenient for many purposes, it has the disadvantage that it works only with re-compilable versions of PHOENICS.

Nowadays therefore most users prefer to make use of the later-developed In-Form feature which attains the same ends without the writing of any Fortran, and therefore also without re-compilation.

In-Form has rendered both PLANT and user-programming superfluous; but both are still available for those who prefer them.

### PLATE, a PHOENICS-VR object type

The PLATE object represents a zero-thickness obstacle to flow, which may be porous. See the description in the PHOENICS_VR Reference Guide, TR326

### PLINE

------------ PIL Graphics command ----

The syntax is : PLINE(X1,Y1,X2,Y2,ICOL,IDASH)

This draws a line between screen co-ordinates (X1,Y1) and (X2,Y2) in colour ICOL and dash IDASH. The range of screen co-ordinates is 0.0 to 1.0 for both X and Y.

### Pline

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

If you type in a series of points in the input window, PHOTON will join them one by one with straight lines to form a multiline.

### PLOT_SURFACE, a PHOENICS-VR object type

A PLOT_SURFACE object is used to declare a surface on which contours or vectors can be displayed. It has no effect on the solution. See the description in the PHOENICS_VR Reference Guide, TR326

### Point, setting of

(see GSET (P,...))

(see SOLUTN)

### POINTS

---- Autoplot Help ----

PO[INTS]
Command only active for PHOENICS restart files. Forces plotting of all variables (including scalars) at cell faces. Return to cell-centre/cell-face operation by repeating POINTS.

### POINT_HISTORY, a PHOENICS-VR object type

A POINT_HISTORY object defines a single cell transient monitor point. See the description in the PHOENICS_VR Reference Guide, TR326

### POLIS

The Phoenics On-Line Information system, introduced with PHOENICS Version 2.0

### POLRA

----------- PIL real; group 13 -----------

POLRA... is used to specify the flow speed on patches, with names beginning with POL, for BFC cases.

See GXPOLR for further information.

### Polygon

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

If you type in a series of points in the input window, PHOTON will join them one by one and close it automatically once a line with only the single carriage return has been typed in. The closed space will be filled with the current colour.

### PORIA

----------- PIL real; group 19 -----------

PORIA... is used in the specification of porosities that depend, dynamically, upon pressure for cells for which IZ is no greater than IPORIA.

See the help and encyclopaedia entries on POROSI, and GREX, GXHOL, for further information.

### PORIB

----------- PIL real; group 19 -----------

PORIB... is used in the specification of porosities that depend, dynamically, upon pressure for cells for which IZ is no greater than IPORIA.

See the help and encyclopaedia entries on POROSI, and GREX, for further information.

### POROSITY

Porosities are factors usually, but not necessarily, less than unity, which multiply (before they are used for convection or diffusion fluxes or for sources) the east areas, north areas, high areas or volumes of designated cells. West, South and Low areas are changed automatically in accordance with what is determined for the East, North and High areas of adjoining cells.

In order to set and use porosities, it is necessary either to use the CONPOR command or to do each of the following:

1. Select an unused variable-index number for each porosity needed,
eg EPOR=18; NPOR=19; VPOR=20 .
2. Give each a name eg NAME(18)=EPOR; NAME(19)=NPOR,etc.
3. Provide the relevant storage by the commands SOLUTN(EPOR,Y,N,N,N,N,N) etc.

(Note that items 1, 2 and 3 can alternatively be achieved by means of the keyword command, STORE(EPOR,NPOR,VPOR), but the stores then taken will be the first unused ones, working backwards from NPHI.)

4. Set the required initial values in GROUP 11 by means of FIINIT and of PATCH (with INIVAL or LINVLX etcthe "type"), and of INIT with suitable arguments.

If porosities are to be changed during the course of execution, suitable coding must be introduced into a GROUND subroutine, an example of which is subroutine GXPORA called from GREX.

It should be remembered that PATCH and COVAL here act in an additive manner (when INIADD is T). Thus if HPOR (say) is to equal 1.0 over most of the domain but 0.2 over a small portion of it, it will be best to set:

• FIINIT(HPOR)=1.0 followed by:
PATCH(name,INIVAL, , , , , , , , ) and
INIT(name,HPOR,0.0,-0.8) ; for this will
subtract 0.8 from 1.0 to give the required value.

The same field initialization can be achieved by the following commands:

FIINIT(HPOR)=1.0 followed by
PATCH(name,INIVAL, , , , , , , , ) and
INIT(name,HPOR,0.0,0.2) ; for this will overwrite 1.0 by 0.2 to give the required value.

Porosities can be printed out in precisely the same way as other variables, viz by OUTPUT(variable name,,,,,,)

Porosity factors have in the past been used for the representation of solid obstacles present in the domain, cells that are full of solid material being given volume- and cell-face-porosities of zero.

This practice is no longer necessary or recommended. Direct use of the property-marker variable PRPS being preferred.

See also the entries for: PATCH, TYPE, INIADD, INIT, INIVAL, LINVLX, LINVLY, LINVLZ and CONPOR for further information.

(see EPOR)

(see HPOR)

(see NPOR)

### PorosityCheck ON/OFF

(Setup Menu)----------- PorosityChe Photon Help ----

[Porosity ON/OFF] where the variable VPOR has been stored, PHOTON will automatically disable plotting vectors and contours within cells where VPOR=0.0.

If it is required to plot within blocked cells, then [Porosity OFF] will disable the porosity checking within PHOTON.

[Porosity ON] will restore checking.

### Position

[Position] shows the position (bottom-left corner) of the current text string in the plotting window. It can be modified by typing in the new window co-ordinates.

### POTCMP

--------- PIL logical; group 19 ---------

POTCMP... is used to activate, for potential flows, a correction for compressibility.

See the encyclopaedia entry on potential flows, and GREX and GXPOTC for further information.

### Potential flow

#### Introduction

"Potential flow", also called "ideal-fluid flow" or "irrotational flow", is a mathematical concept to which real flows approximate only in special circumstances, namely those in which:

• viscous effects are absent; and
• compressibility effects are small.

Their distinguishing mathematical feature is that the velocity field obeys the equation:

velocity vector equals minus grad POT
where POT is a scalar, called the "velocity potential".

Combination with the mass-conservation principle, which states that

the divergence of velocity (multiplied by density if this is non-uniform) is zero,
leads to the so-called "Laplace Equation" for POT, namely:

where rho is the local fluid density.

#### Solution by PHOENICS

Equations of this kind can be very easily solved by PHOENICS; for they are similar to the simplest-possible heat-conduction equation, namely that which is valid when the thermal conductivity is uniform and heat sources are absent.

If therefore the statement:

SOLVE(POT)

is placed in the Q1 file, and appropriate boundary conditions are provided, PHOENICS will generate the values of the velocity field throughout the domain.

From these, the components of the velocity vector can be obtained by differentiation; and indeed this is done automatically by PHOENICS if the Q1 also contains the statements:

• POTVEL=T; and
• STORE(U1, V1, W1).

If, in addition, the Q1 contains:

• STORE(P1)
the pressure, or rather the difference of the pressure from the value of FIINIT(P1) , will also be automatically computed and printed.

Because the equation is linear, only one sweep through the domain is needed, provided that the whole-field solver is used (if NZ >1) and LITER(POT) is set to a sufficiently large number.

Examples may be found in the Input-File Libraries; thus:

• case 126 which shows how to compute the ideal-flow field around a plate inclined to the flow. [Click here to see the velocity vectors];
• case 128 which shows how to compute the ideal-flow field around a model Formula-1 racing car.
• case 129, which shows how In-Form can be used so as to define the source-sink distribution which has the same effect on the flow as a solid body immersed in it. [Click here to see the streamlines and potential contours]

#### Compressible potential flow

PHOENICS can also solve the compressible-flow potential equation, by making Gj a function of the local Mach number.
Core-library case 117 provides an example. Because the Mach-number distribution is not known at the start, an iterative (ie multi-sweep) procedure has to be adopted. The relevant PIL setting is POTCMP = T; and this activates calls to subroutine GXPOTC in file GXMODS.F.

#### An (older) alternative method

An alternative method is based on the analogy which exists between the potential-flow equations and the equations that govern flow in a highly-resistive medium.

The command DARCY=T activates these latter equations, and results in solutions for the velocity fields and the pressure.

The velocity-potential is proportional to the DARCY pressure, the constant of proportionality being the reciprocal of the resistance coefficient used in the COVALs for the velocities, which by default is 1.E5.

This method is less economical than solving for the potential directly, because it necessitates the solution of u, v, w and p.

It is however of historical interest, because it was the first method used in PHOENICS for solving the potential-flow equations; and it illustrates the flexibility of the PHOENICS structure. Core- library case 275 uses the technique; and library case B514, and others, show that it can be used with body-fitted coordinates.

### POTVEL

--------- PIL logical; group 19 ---------

POTVEL... is used to activate, for potential flows, the calculation of velocities from the potential gradients.

See the encyclopaedia entries on potential flows, GREX and GXPOTV for further information.

### POWER /POWER X /POWER Y

---- Autoplot Help ----

POW[ER] {dir} {f} {i j}
The X (or Y, as specified by 'dir') coordinates of elements i-j will be raised to the power f. SCALE will redraw the plot correctly scaled to the new values.

### The PQ1-Editor

This executable, pq1ed.exe, has been created by CHAM in order to facilitate the writing of parameterized Q1 files in the format enabling their use as the basis of Simulation Scenarios. It can also be used as a general-purpose text editor which possesses numerous convenient features, an overview of which can be seen by clicking here.

Especially noteworthy are:

• the code-completion feature, which facilitates the making of single-line entries, and
• the text-macro feature, which facilitates the inclusion of larger bodies of text.

Moreover both of these can be customized by the user to suit his own purposes.

### Prandtl energy model

See PHENC entry Prandtl energy with prescribed length scale

### Prandtl mixing-length model

See PHENC entry Prandtl mixing-length model

### Prandtl number: a dimensionless transport property, defined as:

• the kinematic viscosity divided by the thermal diffusivity, for heat transfer, and
• the kinematic viscosity divided by the material diffusion coefficient when material transfer is in question.

PHOENICS allows each transported quantity to be characterized by two distinct Prandtl numbers, the first relating to the laminar contribution to transport and the second to the turbulent contribution.

The variables expressing their values are, respectively:

These variable are also used, alternatively, for setting:-

• the thermal conductivity when heat transfer is in question, and
• the material diffusivity (with dimensions length**2 / time) for mass transfer.

That this alternative meaning is to be used is signalled by setting the value of PRNDTL to the negative of the desired value.
Thus if the thermal conductivity is to be set to xxxxx, the Prandtl number for enthalpy or temperature (according to which is being solved for) must be set to - xxxxx .

### Preliminary print-out

(see GROUP 20-24)

### Prescribed effective-viscosity model

See PHENC entry Prescribed effective viscosity model

### PRESS0

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

PRESS0....parameter representing the reference pressure, to be added to the pressure computed by PHOENICS in order to give the physical pressure needed for calculating density and other physical properties.

The use of this variable is strongly recommended in cases in which the static component of the pressure is much greater than the dynamic head. The reason is that the static component can be absorbed in PRESS0 leaving the stored pressure field, ie. P1, to represent the dynamic variations which otherwise may be lost in the round off, according to the machine precision and the ratio of dynamic variations of pressure to the static head.

This use of PRESS0 is typified in the Input Library cases that compute the flow in the combustion cavity of reciprocating engines.

(see IPARAB)

### PRESSURE RELIEF, a PHOENICS-VR object type

A PRESSURE RELIEF object defines a single cell fixed pressure point. See the description in the PHOENICS_VR Reference Guide, TR326

### Presumed-pdf model

See PHENC entry Presumed-pdf model

### PRINT0

PRINTO is an EARTH real variable which determines whether small quantities shall be printed as zero. Its default value is 1.e-11

Users desiring to change this to 0.0, say, should insert, at the top of the Q1 file, the sequence:

prt0begin print0 0.0 prt0end

This sequence will be read by EARTH as a consequence of the CALL RQ1R statement in section 2 group 1 of GREX3.F

This method of data-transfer to EARTH has been adopted temporarily so as to avoid increasing further the number of SATELLITE-readable variables.

### Private directory

Any directory from which users run PHOENICS programs. Private directories are frequently (but not necessarily) under PHOENICS. Private directories must have all the files present in the "model" private directory d_modpri. The directory d_priv1 in the PHOENICS standard installation is an example of a private directory.

### Private version

A version of a PHOENICS program that has resulted from the modification, compilation, and linking of an original PHOENICS module by the user. Private versions normally reside in private directories.

### PRLC1A

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

PRLC1A....parameter used in formula for laminar Prandtl number of phase-1 concentration C1. Further variables of the same kind are: PRLC1B, PRLC1C, PRLC2A, PRLC2B, PRLC2C, PRLC3A, PRLC3B, PRLC3C, PRLC4A, PRLC4B, PRLC4C. The 1's,2's ...etc refer to concentration variables, C1, C2, C3 and C4.

### PRLH1A

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

PRLH1A....parameter used in formula for laminar Prandtl number of phase-1 enthalpy. Further parameters of the same kind are: PRLH1B, PRLH1C.

### PRNDTL

---- PIL real array; default=1.0; group 9 -

PRNDTL(phi).... if positive, sets the laminar Prandtl number of variable phi.

If it is negative, but not equal to GRND, GRND1, etc, the LAMINAR DIFFUSIVITY of variable phi is set equal to
ABS(PRNDTL(phi)),
with dimensions: length**2/time.

For TEM1 andTEM2, however, negative values denote thermal conductivities, not diffusivities.

PRNDTL(phi) = GRND, GRND1 etc, for a GROUND-set array of laminar Prandtl numbers for variable phi at each slab IZ.

PRNDTL(phi) = -GRND, -GRND1 etc, for a GROUND-set array of laminar diffusivities for variable phi at each slab IZ.

PRNDTL(phi) = GRND1 sets the Prandtl number to the local value of the whole-field variable named PRL, created in Group 7 by the command STORE(PRL), which can be set by FIINIT and PATCH/INIT commands in Group 11.

In two-phase flows, PRNDTL(9) and PRNDTL(10) control the pertinent phase diffusion of mass for phase 1 and phase 2 respectively. However, they must then be set equal to each other; for when phase 1 diffuses out of a cell, an equal quantity of phase 2 must diffuse in.

### PRNTIM

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

PRNTIM....This command prints out the current machine clock time with a character string in front of it. For example, PRNTIM(HELLO) might print out the following line:
HELLO 2001 7 16 15 52 31
wherein the numbers signify:
year month day hour minute second

### PROFA

----------- PIL real; group 13 -----------

PROFA, PROFB, PROFC and PROFD are used in the specification of power-law inlet profiles.

See GXPROFIL for further information.

### PROFIL

---- PIL real flag; value=24.0; group 23 -

PROFIL....is a PATCH type which indicates that a profile of the variable indicated is to be plotted along the line indicated by the arguments of the PATCH command.

The number of columns to be occupied by the plot when IPROF =0 is fixed by the value of the index NCOLPF, the default value of which is 67. For IPROF greater than zero, the dimensions of the plot are governed by ABSIZ and ORSIZ.

(see NTZPRF)

(see NCOLPF)

### PropertyCheck

[PropertyCheck ON/OFF] where the variable PRPS has been stored, PHOTON will automatically disable plotting vectors and contours within cells where PRPS > 100 (set in Q1 file).

If it is required to plot within blocked cells, then [PropertyCheck OFF] will disable the property checking within PHOTON.

[PropertyCheck ON] will restore checking.

### PROPX

A synonym for GRND1. It means "proportional to xulast", and is used for determining the z-direction interval for parabolic flows.

### PROPY

A synonym for GRND2. It means "proportional to yvlast", and is used for determining the z-direction interval for parabolic flows.

### PRPS

#### What it is

PRPS is a whole-field variable used in EARTH and GROUND coding for indicating which material lies within each cell of the grid.

It is activated by placing the STORE(PRPS) command in the Q1 file.

#### Assigning values

Values of PRPS must then be supplied for each cell in the domain, by means of either:

• the PIL statements:
• FIINIT(PRPS) = value, for the 'domain' fluid, usually that which fills the whole domain except for the parts occupied by solids;
• PATCH(..... and INIT(...,PRPS,0.0, value), commonly used for stating where the solids are and what material they consist of; or
• (INITIAL of PRPS is .... with ...), when In-Form is in use, for either fluids or solids.

• or Fortran coding, perhaps created by PLANT, when the recompilable version of PHOENICS is available.

Note that, in a two-phase calculation, PRPS may be used to set the properties of phase 1 only.

#### The PROPS file

Each assignable value denotes an individual material, of which the properties are defined in the file called PROPS, which resides in d_earth. Examples are;

0 denotes air at 0 deg C and 1 atm pressure;
2 denotes air obeying the Ideal Gas Law; and
67 denotes water at room temperature.

The PRPS values are also referred to as "material indices" or "material flags"; and they are given the symbol IMAT in GROUND coding.

The whole file can be viewed by clicking here.

#### SOLPRP, PORPRP and VACPRP

Three values of PRPS are of special significance, They appear at the head of the PROPS file thus:
``` SOLPRP 100.0
PORPRP 198.0
VACPRP 199.0```
SOLPRP is the lowest PRPS value belonging to any solid (aluminium metal in the current version).

PORPRP denotes a solid which interacts with the fluid hydrodynamically, so that the no-slip condition prevails at its boundary, but not thermally.

VACPRP denotes a solid which interacts with the fluid only by preventing access to the space which it occupies; the no-slip condition therefore does NOT apply at its boundaries; and these are adiabatic.

Within the solver module of PHOENICS, the PRPS value prevailing at each cell is checked. All those with values greater than 199 are treated as solids; and all those below 198.0 are treated as fluids.

#### Where PRPS = -1.0

A feature introduced with PHOENICS version 3.4.3 is the facility to set the PRPS-value of selected cells equal to -1.0 .

For these cells, the material properties are deduced not from the entries in the PROPS file but from the values of RHO1, ENUL, CP1, PRNDTL(temperature) etcwhich are set in the Q1 file and transmitted via EARDAT.

#### Other sources of information

See PHENC entries: PROPERTIES and PROPS.

### Protected mode of Satellite operation

#### Some history

In 1998 the PLANT feature was introduced into PHOENICS. This allowed formulae to be placed in the Q1 file, which after interpretation by the satellite, caused corresponding Fortran coding to be created, compiled and linked to the solver module.

Then in 2001 the In-Form feature was introduced. Its purpose and effect were the same, namely to allow users to extend the simulation capabilities of PHOENICS; but it did so without requiring Fortran coding to be created, compiled or linked into a new executable.

Both PLANT and In-Form statements had to be protected from the obliterating tendencies of the VR-Editor, by 'SAVE' markers placed before and after them; these warned the Editor to save the statements and place them properly in the Q1 file which it was writing.

In 2007 it was recognised that a similar device could be used to protect those advanced-PIL statements (declarations, IF-statements, relationships, etc which the Editor should not be allowed to obliterate.

Thus came into existence the 'protected mode' of satellite operation, the operation of which will now be illustrated.

The information is also available in pdf format here.

See also the Encyclopaedia entry on q1 files and parts 1 and p2 of a tutorial about how to create parameterised Q! files.

### PRT

------- PIL real array; group 9 ------------ default= 12*1.0,1.314,(NPHI-13)*1.0;

PRT(phi)....sets the turbulent Prandtl number of variable phi, if it is greater than zero. If it is less than zero, it sets the turbulent DIFFUSIVITY of variable phi to ABS(PRT(phi)).

PRT values can not be set in GROUND.

In two-phase flows, PRT(9) and PRT(10) control the phase diffusion of mass in phase 1 and phase 2 respectively.

### PRTSIZ

--------- PIL logical; group 10 ---------

PRTSIZ... is used, in two-phase calculations for droplets using the "shadow" method, to activate a multiplication of the interphase friction term by a ratio to take into account the variation of droplet size with time.

See the help and encyclopaedia entries on INTERPHASE, and GREX and GXDROP for further information.

### PTEXT

------------ PIL Graphics command ----

The syntax is : PTEXT(TEXT,X1,Y1,ICOL)

This writes the specified TEXT at screen position (X1,Y1) in colour ICOL. The range of screen co-ordinates is 0.0 to 1.0 for both X and Y.

### PTIME

------ PIL Graphics Command ----------

The syntax is : PTIME(L1,L2,ICOL,IDASH)

This draws a section of time step distribution in colour ICOL and dash type IDASH. L1 and L2 are the limits.

If ICOL is less than 1, then its effect is similar to that with GGRID; the same is true for IDASH.

### Public version

Unmodified version of a PHOENICS program, as supplied by CHAM. Public versions are normally kept in the corresponding program directory (for example, d_satell for SATELLITE).

### PWLF

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

PWLF is a PIL function to perform a linear interpolation in a table read from a file. The format of the command is:

Yvalue = PWLF(file_name, Xvalue)

Yvalue is the output of the function. It can be directed into any valid PIL variable or command.

file_name - is the name of the file to be read. Within the file, blank lines are ignored. Lines starting * or # are ignored. Anything after ! is ignored. The file can contain any number of lines, but only two columns. Each line must contain two columns. The first active line may optionally contain character strings defining the names of the columns. Space(s), comma, semi-colon or tab can be used as separators between columns.

Xvalue - is the value of X at which Y is to be evaluated.

As an example let the file ethalpy.csv contain the values of enthalpy (ENT) as a function of temperature (TEM):

```  TEM,            ENT
-17.8   ,      -1238746.805
4.4     ,      -1171705.951
26.7    ,      -1104278.562
48.9    ,      -1037069.369
71.1    ,      -969776.1961
93.3    ,      -902399.0434
115.6   ,      -834633.8417
137.8   ,      -767088.3508
170     ,      -668967.72
197.5   ,      -585029.1675
```

To extract the value of enthalpy at 50 deg, one could use:

```REAL(HVAL,TEMVAL)
TEMVAL=50.
HVAL=PWLF(ENTHALPY.CSV,TEMVAL)
```

PWLF can also be used as an InForm function to be executed at solver run-time.

wbs