Encyclopaedia Index


Angled in- and outlets Angled plates
Application Album
Automatic Grid Generation Automatic meshing
AWSR. i.e.time-Average Well-Stirred Reactor


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

Command to terminate Satellite run without saving data.


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

[Abort] the current setting and reset the plotting queue to the original order.


----- PIL real; default= 0.5; group 23 -- -

ABSIZ....sets the horizontal extent of the abscissa in plots of residuals and monitor values, and in PROFIL plots for which IPROF is greater than zero.
The default value gives a plot with 50 columns.

See also ORSIZ.


(File Menu)------------------------------------- Photon Help ----

[Accept] will take the current menu setting and open PHI(DA) and XYZ(DA) files.


(Save Menu)------------------------------------- Photon Help ----

Accept the file name and the title then save the screen contents as a new frame in the save-file.


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

[Accept] the current setting for the block region.


ACCUTM, a utility which computes the time spent by PHOENICS in the execution of defined Fortran sequences.

The Fortran statements which have to be included are as follows:

CALL ACCUTM('this 1',1)

CALL ACCUTM('this 1',2)

This counts the accumulated time between the calls with second arguments 1 and 2; and the call with second argument 3 causes print-out of that time.

It should be noted that the execution of ACCUTM itself occupies some time, the amount of which has to be determined machine-by- machine.

The name of the sequence (here 'this 1') should be a six-character variable.


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

ADDDIF....When T, includes viscous contribution to momentum transfer in pressure-correction coefficients. The formulation requires the distance to the nearest wall, so the command DISWAL should also be used.

ADDITIONAL equations solved by PHOENICS

(Note: this entry is best read after reading that on differential equations solved by PHOENICS)

"Closure" of the equation set

In order that the differential equations solved by PHOENICS should constitute a soluble set of equations, additional equations must be supplied, which supply information about the auxiliary variables and the boundary conditions.

Auxiliary-variable specifications

In general, an auxiliary variable a1 (say) can be an algebraic function of the other auxiliary variables a2, a3, etc. and of the dependent variables p1, u1, ..., c135:

a1 = f(a2, ...,an; p1, u1,...,c135)

An example of such a function is the ideal-gas law for density:

rho1 = P1 * W/(R*T)

where W is the molecular weight, R is the universal gas constant and T is the temperature.

PHOENICS is equipped with many formulae for the auxiliary variables as switch-on options; but it also permits users to supply their own if they wish. (See PHENC: AUXILIARY)

Boundary conditions

The need for boundary-condition information can be demonstrated by integration of the governing differential equation over the whole volume of the domain, with the result:

d(ri*rhoi * Fi)/dt + div(ri*rhoi*Vi*Fi - ri*Gf,i*grad(Fi)) = ri*Sf,i

Volume integral of [ri*Sf,i - d(ri*rhoi*Fi)/dt] = Surface integral of [(ri*rhoi*Vi*Fi - ri*Gf,i*grad(Fi)]norm

Evidently, what have to be specified at the domain surface are the convective and diffusive fluxes normal to the surface area, i.e.:

[ri*rhoi*Vi*Fi]norm & [- ri*Gf,i*grad(Fi)]norm

By default, PHOENICS takes these fluxes as zero at all boundaries of the domain. The boundary-condition-defining task is to identify the patches of the domain surface at which non-zero fluxes are required, and to specify the fluxes which apply there.

The pressure variable, P1, is associated with the continuity equation. Integration of this equation over the domain volume, followed by application of the divergence theorem, shows that what has to be specified at the domain surface is the mass flux normal to the surface, i.e.,


Thus, the boundary-condition data for P1 determine the mass-flux specification.

Interior surfaces are represented in the same way as exterior surfaces.


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

ADJEPR...by the distance when set to true, activates a multiplication of the EPOR variable distance between cell centres in the x-direction which is used in thin-film lubrication cases. See GREX3 for further information.


AEAST is an integer index, used in GROUND to access an array containing the 'free' east-face area after blockages are deducted, at the current z-slab.


AHIGH is an integer index, used in GROUND to access an array containing the 'free' high-face area after blockages are deducted, at the current z-slab.


See also the lecture and the open-source coding.

1. Description of model

The Algebraic Slip Model is provided in PHOENICS to simulate multi- phase processes. It is based on the assumption that there is a single continuous phase containing other dispersed components whose motion (slip velocity) relative to the continuous phase is given by an algebraic relationship involving local hydrodynamic variables.

PHOENICS solves for variables associated with the flow in the usual manner for a single-phase fluid; now however the variables are to be associated with the mixture. Local volume fractions for each component (including the continuous phase) are then determined from individual conservation equations, with the constraint that the component fluxes across each cell face should be compatible with the corresponding mixture flux.

Solution of all component conservation equations is carried out together at the end of the slab solution of the mixture hydrodynamic variables, using cell and slab iterations.

The slip velocity for each component is the local equilibrium or terminal velocity: this is reasonable if the time scale of the changing hydrodynamic conditions experienced by the dispersed components is much longer than the time scale on which the droplets, bubbles or particles adjust to them. The slip velocity is derived from a conventional drag coefficient formulation. The drag coefficient, CD, is given by max(24/Re,0.42), where Re is the Reynolds number based on slip velocity and droplet, bubble or particle diameter; alternative expressions can easily be coded if required.

Mixture properties are determined as linear combinations of individual component properties, based on volume fractions; different formulations can easily be introduced if required.

2. Implementation in PHOENICS

Please see the lecture on the algebraic slip model in the multi-phase-flow section of the general lectures on PHOENICS.


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

[Allgrids] switches all GRID elements ON/OFF. It is not an attribute of the current GRID element.


---- Autoplot Help ----

ALN [X or Y]
Takes the exponential of the x or y axis of all data elements. SCALE will give a correctly scaled plot. See also HELP on : LN, LOG, ALOG, SCALE


---- Autoplot Help ----

ALO[G] [X or Y]
Takes the anti-log of the x or y axis of all data elements. SCALE will give a correctly scaled plot. See also HELP on :


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

The starting positions of the streamlines will be uniformly distributed along a straight line in the projection of the initial plane defined by [InitPln] in the STREAMLINES menu.

After pressing this button, PHOTON prompts you to supply the number of streamlines.

Angle of slope, specifying the sine of

(see SNALFA)


---- PIL real; default=20.0; group 6 ----

This is used when performing a grid-orthogonality check with the GRDCHK command. The indices of any cell having an angle below ANGMIN will be displayed. ANGMIN may be reset by the user. The units of ANGMIN are degrees.


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

ANGVEL... is the angular velocity used by GXROTA to calculate the rotational source terms for cylindrical-polar and BFC cases: see the help on ROTA for further information.


ANORTH is an integer index, used in GROUND to access an array containing the 'free' north-face area after blockages are deducted, at the current z-slab.


See PHENC entry: F-array of EARTH


(Geometry Menu)---------------------------------------- Photon Help ----

[Arc] draws an arc by typing in three points in the input window.

ARC command in PHOTON

The ARC command in PHOTON is used to plot circles and circular arcs. An arc or circle is defined by 3 points in 3D space, the order of which is significant in the case of an arc, as it determines the direction in which the arc is drawn.

An ARC command consists of four command lines: the first of these contains the line type, the line colour, and the 'circle' indicator (0 means draw an arc, 1 means draw a circle). The remaining three command lines define the cartesian coordinates of 3 points on the arc.

Here is an example of an ARC command:

In this case, a full circle will be drawn in line type 1 and colour 6 through the three points specified. If an arc were specified rather than a circle, then the line would be drawn from point 1 (0.1 0.1 0.1), through point 2 (0.2 0.3 0.4) to point 3 (0.5 0.5 0.5).


(see ARC command in PHOTON)

Argument-setting commands

(see PIL)



ARITHMetic....the PHOENICS Input Language (PIL) can, in addition to simple assignment statements of the type name=value, also express arithmetic. The operators recognized are +, -, * , / and ** . The delimiters recognized are the brackets ( and ). The standard trigonometrical functions, such as COS and SIN, are also recognized.

Numerous examples of the use of PIL arithmetic are provided in the PHOENICS Input Library.

See also PHENC entry:PIL


----- Command; group 1 ---------------

PIL users may declare and access their own arrays. The syntax of an array declaration is:


where type is INT, REAL, CHAR or LOG depending on the type of array being declared, and d1, d2 and d3 are integer expressions defining the dimensions of the array. The maximum number of dimensions of an array is 3. Examples are:

Character-array elements are 68 characters long and defaulted to ' ', integer arrays have default values of 0, real arrays of 0.0 and logical arrays of F. However the name of the character array , e.g. ARR1 above, may not exceed 6 characters.

Array expressions can be used on the right- and/or left-hand sides of expressions, with the limitation that, on the right-hand side, array indices can be only simple variables or positive constants.

Examples are:-

It should be noted that CHARACTER array elements must be evaluated between colons in order to yield their values on the right-hand-side of expressions, as in the third example above.

Attempts to access an array element outside the declared bounds will elicit an error message.

The maximum number of arrays which can be declared is 100.

The amount of space reserved for array elements is determined by the PARAMETERS MXISP,MXRSP, MXCSP and MXLSP which are declared in routine ARRJB in the file SATLIT.FTN. These can be reset by the user to increase the amount of array-space available.

The XC, YC and ZC arrays (see Group 6) can be accessed on the right-and left-hand sides of expressions, eg:

The indices in the corner co-ordinate arrays can be constants or simple variables only. Thus the following is ILLEGAL:


Arrays, declaring and accessing

(see ARRAY)


ASLP is a PIL logical variable which activates the Algebraic SLip Model q.v. for multi-phase flow.
See also and encyclopaedia entries on GREX3 and Advanced multi-phase flow for further information.


An ASSEMBLY object acts as a 'container' for several linked objects. See the description in the PHOENICS_VR Reference Guide, TR326


... an abbreviation sometimes used for Algebraic Slip Model)


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

The starting positions of the streamlines are picked up with the cursor one by one in the projection of the initial plane defined by [InitPln] in the STREAMLINES menu.


(see CONFIG)


Since 2007, PHOENICS has been capable of using unstructured grids for its calculations, as well as structured ones.

Now, in 2009, an automatic grid-generation capability has been added which, starting with a coarse grid and a set of instructions provided by the user in the Q1 file, subdivides the cells systematically, in the vicinity of solid object, inlets and outlets, so as produce an unstructured grid having the smallest cells in the regions which most need them.

It can also be used in a solution-adaptive manner, which provides refinement in regions which can be determined only after the solution process has begun.

A full account of this facility can be accessed by clicking here.


---- PIL logical; default=F; group 24 --- -

AUTOPS....EARTH can work in the so-called "autopsy" mode, which permits a user to perform a thorough analysis of the SAVEd results by the performance of a series of single-sweep runs which print but do not solve.

Provided that SAVE was set T in a previous run, an autopsy run can be performed by the instructions:
together with any desired output options.

For example:

Of course, precisely because no further solution operations are conducted in an autopsy run, the only results which can be printed and plotted pertain to the end of the previous run; and imbalances in equations cannot be printed correctly.


Auxiliary variables are distinguished from dependent variables by being derived from algebraic equations rather than from differential ones. Examples of auxiliary variables are:

When such variables are constants, they are represented in PHOENICS as scalars. When non-constant, they can (if desired) be stored as field variables by adoption for this purpose of one or more of the 50 dependent-variable stores.


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

[Average] sets the averaging method for vector calculation in BFC cases. When [Average] is set [No], only the High, North and East values of the Cartesian components for each cell are used.

However, if it is set [Yes], all six Cartesian components are used. This may affect the resulting velocity vector in some cases.


---- Autoplot Help ----


Alternately removes and replaces x and y axes. Default ON. See also HELP on : BOX, FRAME, TICK, EQUAL, UNEQUAL, SCALE

Axes Systems

PHOTON by default uses the right-handed co-ordinate system. You may, however, switch between the left-handed and the right-handed systems. You can use the following SET command options to select the co-ordinate system:

SET LHAND- to select left-handed co-ordinate system; SET RHAND- to select right-handed co-ordinate system.

PHOTON by default uses the right-handed co-ordinate system. You may, however, switch between the left-handed and the right-hande systems. You can use the following SET command options to select the co-ordinate system:

SET LHAND- to select left-handed co-ordinate system;
SET RHAND- to select right-handed co-ordinate system.


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

AZDZ....determines the variation of DZ with z distance.

AZDZ is used, especially in parabolic calculations, for changing the z-direction step size, DZ. If AZDZ is given any constant value other than GRND, the step size is multiplied by the factor (1.0 + AZDZ) at each forward step. The step size so multiplied is always the nominal one which has been set by the SATELLITE (via GRDPWR, or by direct settings of the ZFRAC array elements).

When AZDZ is set equal to GRND, EARTH will expect to find a direct setting of DZ in GROUP 5 of GROUND.


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

AZPH....linear coefficient for the downstream pressure level PBAR .

AZPH (P stands for pressure, and H for high) is a quantity which may be useful in parabolic runs for which IPARAB is set greater than zero; for these are the ones for which the downstream (i.e. high) pressure is set by the user. If AZPH is set to a constant, other than GRND, the downstream pressure will exceed the current-slab pressure by the amount AZPH * DZ. If, however, AZPH is set equal to GRND, EARTH will visit GROUP 14 of GROUND in order to pick up a value of PBAR, which will then be used as the downstream pressure.


------ PIL real; default=0.0; group 19 ----

AZW1....is a parameter used in specification of the movement of the first part of an n-part grid. In the piston-in-cylinder example provided in subroutine GXPIST ( called from GREX ), AZW1 is the rotation rate of the crank in radians/sec.

Setting AZW1=GRND1 activates the constat-piston-velocity option, the value of the velocity being set equal to BZW1 .

See also IZW1, BZW1 and CZW1.


------ PIL real; default= 0.0; group 3 --- -

AZXU....an exponent, which determines the variation of XULAST with z distance. This feature is used in parabolic calculations ( see PARAB ) to enlarge the x extent of the grid with downstream location so as to permit the capture of the lateral growth of jets, boundary layers, wakes and the like.

AZXU, when not equal to 0.0 (its default value), effects a variation of the x-direction extent of the grid, i.e. of XULAST, with variation of distance z. When AZXU is set to a constant other than GRND, XULAST is multiplied at each z-direction step by the factor:
(1.0 + AZXU*DZ/(ZWADD+Z)) .
The cumulative effect of this is an approximate power-law growth, XULAST/(XULAST at inlet) = (1.0+ZW/ZWADD)**AZXU , where ZW is the z-coordinate of the current z step.

When AZXU is set to 1.0, this gives a linear growth of the x-grid width in the z direction, of slope equal to: ((XULAST at inlet)/ZWADD) . Hence, for a desired slope, set ZWADD equal to XULAST at inlet divided by the slope.

If AZXU is set to GRND, it causes EARTH to visit GROUP 3 of GROUND where XRAT is to be set as the factor which will multiply XULAST.


------ PIL real; default= 0.0; group 4 --- -

AZYV....an exponent which determines the variation of YVLAST with z distance.

AZYV has a function similar to that of AZXU; but it effects a stretching or contraction in the y-direction instead, by operating on YVLAST.