Encyclopaedia Index


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The X component.


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Once activated, GRID, VECTOR, CONTOURS and SURFACE will be plotted on each X plane in the current plotting region. In the case of STREAMLINES this option together with the [IniPln] option can be used to specify the initial particle seeding plane.

See also: [PlanNo], [Outline]


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[X] the surface contours will be generated on X plane. Usually two out of three directions (e.g. X, Y or Z) will need to be specified, to generate a cross-hatched surface.

x-,y- and z-direction grid specifications

(see GROUPS 3-5)

X-direction coordinates, setting of

(see XFRAC real array, Group 3)

X-extent, enlarging the grid

(see AZXU real, Group 3)



(See FORTRAN CODING in GROUND for the context)

The EARTH variables in the X-wise, Y-wise and Z-wise categories have only one distinct value for each and every value of the coordinate in question. The lengths of the F-array segments which they occupy are therefore NX, NY and NZ respectively.

Examples are:-
XWV's : the distance (or angle) x from the origin to a cell centre; and the difference in x-value between successive u-velocity locations.
YWV's : the radial distance from the symmetry axis to a cell centre; and the difference in y-value between successive v-velocity locations.
ZWV's : the distance z from the origin to a w-velocity location; and the difference in z-value between successive cell centres.

Because of the slab-by-slab nature of the PHOENICS storage and equation-solving arrangements, there are more ZWV's than there are XWV's and YWV's.

The variables in question are those which appear in the COMMON block /LB/ of GRDLOC as:


---- Real Array; Group 6 ---------------- -

XC....is the Satellite array used for body-fitted coordinate grids to represent the Cartesian coordinate x of the corners of the continuity cells. See also YC, ZC and BODY-F.

XC is also a GROUND-accessible real function returning the corner-coordinate value. See also SUBROU.


When the Q1 file contains BFC=T and STORE(XCEN), the values of the cell-centre x-coordinates are printed in the result file. They may also be accessed and used by In-Form statements.


---- Logical; default=F; group 13 --- -

XCYCLE....set to T activates cyclic boundary conditions along the east and west boundaries of the integration domain.

To activate x-cyclic boundary conditions in BFCs, see entry for the XCYIZ command in Group 6.


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

The syntax is : XCYIZ(IZF[,IZL],FUNC)

This command switches the BFC x-cyclic boundaries over the range IZ=IZF,IZL to FUNC, which may be T, F or any valid PIL logical variable. IZF, IZL may be any valid PIL integers. The parameter IZL is optional in that if only a single plane is required, it may be omitted. Thus ;

XCYIZ(3,T) - switches XCYCLE on for slab 3
XCYIZ(1,NZ,F) - switches XCYCLE off for all slabs

The default setting is off for all slabs. XCYIZ may be called more than once to set cyclic boundaries over separate IZ-ranges.The special provision for BFCs is intended for turbomachinery applications in which cyclic conditions are needed at the entrance to and exit from the blade passage. For example: cyclic boundaries upstream and downstream of a blade cascade which starts at IZ=10 and ends at IZ=20, are activated when BFC=T, by: XCYIZ(1,9,T);XCYIZ(21,NZ,T) .

See also the entry for XCYCLE.


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[XF] specifies the starting I index of the current plotting region. The default value is 1.


----- Real array; default=100*1.0; gro -

XFRAC....is an array for use in setting the x-direction coordinates of the "east" faces of the computational cells used for the balances of all variables except (for NX greater than 1) x-direction velocity components U1 and U2.

Distances (or angles if CARTES=F, so that x is measured in radians), are measured from the low-x (i.e. extreme west) boundary of the flow domain.

XFRAC values may be set by means of any of the methods described for TFRAC.


XG2D is an integer index, usable in subroutines called from GROUND, for accessing the 2D array of values, pertaining to the current IZ-slab, of either:
(for CARTES=T or BFC=T) distances of the centres of the continuity cells from the x=0.0 plane in a Cartesian coordinate system, or:
(for CARTES=F and BFC=F) angular coordinates of the centres of the continuity cells in a cylindrical-polar system.

Note that this index is present only if CALL MAKE(XG2D) is present in Group 1, Section 1 of GROUND.


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[XL] specifies the last I index of the current plotting region. The default value is NX+1 for GRID and NX for other plotting elements.


XRAT is a Fortran real variable, used in GROUND. It represents the multiplier of the previous XULAST which gives the current XULAST.


XU2D is an integer index, usable in subroutines called from GROUND, which has a significance similar to XG2D except that the east faces of continuity cells are involved, not cell centres. Unlike XG2D, XU2D has no significance when BFC=T.

Note that this index is present only if CALL MAKE(XU2D) is present in Group 1, Section 1 of GROUND.


---- Real; default=1.0; group 3 ----- -

XULAST....is the overall length of the integration domain in the x-direction, measured in metres for CARTES=T, and in radians for CARTES=F.

The U in the name is a reminder that the staggered-grid arrangements entail that the extremity of the domain in the x-direction is occupied by a velocity (specifically, U1 and U2) location. Grid points at which pressure, temperature, volume fraction and other scalar quantities are located lie halfway between velocity locations.

In parabolic calculations, XULAST can be changed as a function of downstream location by means of the parameter AZXU.


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XYZ.... is used to specify the name of a PHOENICS BFC grid file (XYZ or XYZDA file) which PHOTON will attach, in order to allow viewing of BFC grids. Before attaching the grid, PHOTON enables the specification grid scaling factors.

When a grid file has been attached for viewing, by means of the XYZ command, all commands which rely upon data from a PHI file (eg. VECTOR,CONTOUR, SURFACE) are invalid, and the PHI command must be used to attach a PHI file before these commands can be used.

See also : PHI file

XYZ command in PHOTON

It is possible to view body-fitted-co-ordinate grids alone within PHOTON without you having to attach a 'fields' file. The XYZ command prompts you to enter the name of the grid file you wish to attach. The default file name will be accepted if you press <Return>. The minimum abbreviation for XYZ is X.

XYZ file

An XYZ file contains the geometric data pertaining to a body-fitted- coordinate system. An XYZ file may either be generated by the PHOENICS satellite or by the users' own grid-generation system.

The geometric data in an XYZ file are used as input both for EARTH calculations and for graphic packages for viewing the geometry and grid distributions.

If the geometry does not change during the calculations, the XYZ file after running EARTH will be the same as that written by the SATELLITE. However, if the geometry does change during the calculation, the geometric data of an intermediate or final stage can be written by way of the DUMP subroutine, and will be automatically distinguished from the original XYZ file by the appending of a numerical suffix, eg XYZ9.

The format of the xyx file can be deduced by fortran-literate readers from the following coding sequence used by EARTH to write the file:

c-------------------------- write corner co-ordinates to the xyz file

        CALL OPENFL(24)
        LU=LUNIT(24)            ! logical unit of xyz file
   31   FORMAT(3I5)             ! 3 integers
   32   FORMAT(5(1PE13.6))      ! 5 reals
        WRITE(LU,31) NI,NJ,NK   ! ni=nx+1 ; nj=ny+1; nk=nz+1  ; nij=ni*nj
        L0XC=L0B(12)-NIJ ; L0YC=L0B(14)-NIJ = L0ZC ; L0B(16)-NIJ
        DO IZ=1,NK              ! loop over nk ni*nj slabs
          L0XC=L0XC+NIJ ; L0YC=L0YC+NIJ ; L0ZC=L0ZC+NIJ ! advance l0xc, yc, zc
          WRITE(LU,32) (F(L0XC+IJ),IJ=1,NIJ)    ! nij XCorners
          WRITE(LU,32) (F(L0YC+IJ),IJ=1,NIJ)    ! nij YCorners
          WRITE(LU,32) (F(L0ZC+IJ),IJ=1,NIJ)    ! nij ZCorners

It implies that, after a single line containing nx+a, ny+1, nz+1, the corner coordinates appear in the order:
z-slab 1; xc values, yc values, zc values;
z-slab 2; xc values, yc values, zc values;
and so on.

This is exemplified by the first lines of xyz file grid1 in the BFC input library, as follows:

    6    6   13
 7.849997E-02 7.089996E-02 6.329995E-02 5.570000E-02 4.809999E-02
 4.049999E-02 7.806993E-02 7.051158E-02 6.295317E-02 5.539487E-02
 4.783650E-02 4.027812E-02 7.678455E-02 6.935066E-02 6.191671E-02
 5.448283E-02 4.704890E-02 3.961497E-02 7.465792E-02 6.742990E-02
 6.020185E-02 5.297386E-02 4.574582E-02 3.851778E-02 7.171333E-02
 6.477034E-02 5.782740E-02 5.088450E-02 4.394155E-02 3.699859E-02
 6.798297E-02 6.140119E-02 5.481939E-02 4.823764E-02 4.165583E-02
-1.689791E-08 8.205440E-03 7.411029E-03 6.616615E-03 5.822208E-03

There are two kinds of XYZ files, usually distinguished as XYZ and XYZDA, of which the former is formatted and the latter is a direct- access file. Users specify which geometry-data file is required by setting XYZDA=T in the PREFIX file to produce XYZDA, or XYZDA=F to produce XYZ.

See also: SAVE


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Enter the name of XYZ(DA) file here for a BFC case.


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[XyzFile] is used to specify the name of a PHOENICS BFC grid file (XYZ or XYZDA file) which PHOTON will attach, in order to allow viewing of BFC grids. Before attaching the grid, PHOTON enables you to specify grid scaling factors.

Once an XYZ file is loaded with this option (by pressing the [Accept] button), only the GRID can be plotted with PHOTON.


------ Logical; default=F; group 23 --- -

XZPR....may be set T for tabular print-out of the fields in x-z (ie. constant-y) planes. The default print-out is in the x-y plane, which is less convenient than x-z ( or y-z ) print-out when the z-wise variation of the flow field is of interest.

See also:-YZPR