This has the disadvantage that grid refinement cannot be effected by simply (say) doubling NX, NY and NZ; one must additionally modify the IXF, IXL, IYF, etc for patches which define their locations in the grid.
Fortunately there exists a solution to this difficulty; or, rather, two: one old and the other new, namely:
A small amount of information on this topic is to be found in TR 326; but more is needed.
PATCH is a PIL command used in a Q1 file to define sections of the domain over which:
PATCH can have 10 arguments, whereby:
PATCH(patch_name, TYPE, IXF, IXL, IYF, IYL, IZF, IZL, ITF, ITL)
However, they may also be algebraic expressions, for example:
PATCH(SOURCE,PHASEM, 1, NX/2, NY/4, NY, 3, NZ/6+1, 8, 10)
PATCH might have only 6 arguments, namely:
PATCH(patch_name, TYPE, OBJECT, object_name, ITF, ITL)
wherein:
Examples of the geometrically-located PATCH are to be found in Input-File-Library case 274 . Click here for RSET and here for PATCH.
Two further points should be noted, namely:
Group 11.Initial field variables (PHIs) PATCH(BODY1 ,INIVAL, 1, 3, 2, 3, 6, 10, 1, 1) INIT(BODY1 ,PRPS, 0.000000E+00, 1.980000E+02) PATCH(BODY2 ,INIVAL, 1, 3, 4, 6, 7, 10, 1, 1) INIT(BODY2 ,PRPS, 0.000000E+00, 1.980000E+02)This however is a manifestation of EARTH's internal accounting; and it has no bearing on the question of which kind of locator should be used.
1 (c) Geometric locators; via dot-patch
A different means of introducing geometrically-located patches is the recently-introduced
dot-patch device.
Description and exemplification can be accessed via the hyperlink. Here it suffices to say that:
PATCH(INLET,WEST,1,1,1,NY,1,1,1,1) ! the no-dot patch PATCH(.INLET,WEST,0,0,0,1000,0,1000,1,1000)
The reason is that grids are artificial entities, necessary for the purpose of perfoming numerical calculations, but forming no part of the physical phenomenon which is to be simulated.
Indeed it is often desirable to perform the simulation with more than one grid, using perhaps a coarse grid at first so as to establish the major features of a flow and a succession of finer ones later, in order to procure greater accuracy. The use of the SPINTO module makes it easy to do so.
In such a successive refinement operation, it would be extremely tiresome to have to change all the IXF, IXL, etc. of the PATCHes each time the grid was changed.
If geometric locators are used, there is no need for this.
The uses of PATCH in the four above-mentioned Groups will now be described separately.
In group 11, the last two arguments are always 1, for the initial values can be set only at time step 1.
The PATCH types operative in group 11 are:
INIVAL, LINVLX, LINVLY and LINVLZ.
PATCH in Group 11 is always followed by one or more INIT commands, each having four arguments, namely: patch name, variable index or name, coefficient, and value.
An example is:
PATCH(START,INIVAL,1,NX/2,1,NY,3,NZ-2,1,1)
INIT(START,U1,0.0,12.5)
This, because the type is INIVAL, will set the initial value of U1 to equal 12.5 if the PIL variable INIADD equals F; but if INIADD=T, the value 12.5 is added to whatever has already been set by FIINIT(U1) and by earlier-appearing INIT commands.
If the variable is being stored but not solved, as would be the case with porosities for example, the value will be retained throughout.
When porosities ( eg. NPOR ) fields are being set, it is important to remember to put FIINIT(NPOR)=1.0, so that no blockage is present in sections of the domain not identified by PATCH.
If it is desired to give the variable initial values which vary linearly with ix, iy or iz, the following steps should be taken:
When INIADD is true, judicious use of the various types of patches permits complicated initial-value variations to be contrived.
For more complicated variations of the initial fields than those provided by the above options, the fourth argument of INIT should be set to GRND. This causes EARTH to visit group 11 of GROUND for an array of GROUND-set VALues for each cell in the PATCH. For example:
PATCH(DOMAIN,INIVAL,1,NX,1,NY,1,NZ,1,1)
INIT(DOMAIN,H1,0.0,GRND)
requires the user to provide in group 11 of GROUND a sequence which fills the EARTH array referred to by the index VAL for INDVAR=H1 at each IZ slab of the domain.
To check that the initial fields are correctly set, the user should set INIFLD=T to cause EARTH to print out the initial fields at the beginning of the calculation.
Uni-directional flows can be initialized by means of the special PATCH names starting IBFC that causes group 11 of GREX3 to call subroutine GXBFC.
The following commands result
in a uniform initial flow at 99.0 m/s, parallel to ZC in a body-fitted grid,
PATCH(IBFC,INIVAL,1,NX,1,NY,1,NZ,1,1)
INIT(IBFC1,U1,0.0,GRND1)
INIT(IBFC1,V1,0.0,GRND1)
INIT(IBFC1,W1,0.0,GRND1)
INIT(IBFC1,UCRT,0.0,0.0)
INIT(IBFC1,VCRT,0.0,0.0)
INIT(IBFC1,WCRT,0.0,99.0)
PATCH....can be used in Group 12 to make local adjustments to the terms in the differential equations.
The following patch- names, in which ? is a 'wildcard' and GP12 can be replaced by an ampersand, cause the terms indicated, for the variable appearing as the second argument of a corresponding COVAL statement, to be multiplied by the third (CO) argument of that COVAL, in the cells occupied by the PATCH.
| Patch-name | terms affected |
| GP12CON? | all convection terms |
| GP12SOR? | all built-in source terms |
| GP12CNE? | east-face convection terms |
| GP12CNN? | north-face convection terms |
| GP12CNH? | high-face convection terms |
| GP12DFE? | east-face diffusion terms |
| GP12DFN? | north-face diffusion terms |
| GP12DFH? | high-face diffusion terms |
For example:
PATCH(GP12CNEW,CELL,IXF,IXL,IYF,IYL,IZF,IZL,f-step,l-step)
COVAL(GP12CNEW,W1,0.0,0.0)
COVAL(GP12CNEW,W2,0.0,0.0)
would cut out the east-face convection terms for the first- and
second-phase z-direction velocity components, in the cells and for the duration indicated
by arguments 3 to 10 of the PATCH command.
'Contact resistances' can be introduced into heat-transfer simulations using GP12DF patches. The ability to multiply the total diffusive conductance, for a particular variable and a particular patch, by the constant appearing as the CO argument of the corresponding COVAL is used. In addition, the VAL argument is given significance.
Specifically, the resistance to diffusion now becomes equal to: (resnom + VAL)/CO, where resnom is the nominal resistance, ie that computed by PHOENICS EARTH.
The diffusive coefficient becomes the reciprocal of the above resistance, multiplied by the cell-surface area.
The feature is useful when it is desired to introduce a "contact resistance" to heat conduction. Then VAL should take the value of this resistance and CO should be set as 1.0.
If it is desired to replace the EARTH-calculated resistance by another, say "resnew", then VAL should be set as resnew*1.e10 and CO should be set as 1.e10 .
I M P O R T A N T
This feature works only for variables for which the harmonic-mean diffusion option has been selected.
PATCH is used in Group 13 to define the areas or volumes over which boundary conditions or special sources are to be set by means of COVAL.
The PATCH types operative in group 13 are:
CELL, VOLUME, PHASEM, FREEVL,
NORTH, SOUTH, EAST, WEST, HIGH, LOW,
FREEE, FREEN, FREEH,
EWALL, WWALL, NWALL, SWALL, HWALL, LWALL,
RGRAD, INFLO, OUTFLO,
Much information about what boundary-condition or source functions are to be exercised
by a patch is conveyed by the name of the patch.
An account of the significance of patch
names is to be found in the PHENC entry: RESERVED NAMES.
PATCH is used in group 23 to define sections of the domain over which plots are to be set by the PLOT command. See PATCH in group 13 for the significance of its 10 arguments.
The PATCH-types that are operative in this group are PROFIL and CONTUR.
If the name of the PATCH starts with the letters TAB, the values of the variable used in the plotting of CONTUR maps will be printed out as a TABle before the map is printed.
If the name starts with the letters TBO (ie. TABle Only), only the table will be printed.
The fourth argument of the COVAL (VAL) has no significance in this case.
Sometimes it is desirable to de-activate PATCHes. In a Q1 file, this can be achieved by simply converting the PATCH statement into a comment by shifting it 2 or more columns to the right by means of the system editor. An alternative which also permits PATCH de-activation in an interactive session is to set the PATCH name to SKIP. See SKIP for further information.
If the grid has been divided into regions (ie if NREGi > 1, for i=X,Y,Z or T), then PATCHes (and CONPOR commands) may be set over whole regions in any direction by setting the last 8 arguments as #ireg, ie: PATCH(name, TYPE, #iregx-first, #iregx-last,... #iregt-first, #iregt-last).
Also, $ireg or %ireg may be used to specify patches applying to the first or last cell in a region respectively, eg: PATCH(name, TYPE, $2, $2, #1, #1, #1, #NREGZ, #1, #NREGT) would specify a PATCH over the first cell in the second region in the x-direction, over region 1 in the y-direction, over all regions in the z-direction and for all time regions.
If subroutine PATCH is called from SATLIT in FORTRAN, the symbols $, % and # are not
recognised. Thus to set PATCHes by region numbers use
100000+<region number> instead of $<region number>
200000+<region number> instead of %<region number>
300000+<region number> instead of #<region number>
For example, the following PIL command:
PATCH(AAA,VOLUME,$1,$1,#1,#2,%3,%3,1,1)
would become
CALL PATCH('AAA ',VOLUME,100000+1,100000+1,300000+1,300000+2, 1 200000+3,200000+3,1,1)
in FORTRAN.
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:
-CO*PHI*NAME**VAL
where CO is the third argument of the COVAL, and NAME stands for the local value of the variable having the name which has been referred to.
An example which provides a source equal to - 4.0*KE*VOSQ**0.5 is:
SOLVE(VOSQ,KE);REAL(CONST1);CONST1=4.0
PATCH(*VOSQ1,1,NX,1,1,1,1,1,1)
COVAL(*VOSQ1,KE,CONST1,0.5)
The feature is illustrated by library cases 413, 414 and 415. See also PHENC entry: star-name
If the referenced variable has a 2-character name, the patch name must include the blanks, because the internal-to-EARTH test is made on the first 5 characters of the PATCH name.
Thus:
PATCH(*P1 A,... ) followed by COVAL(*P1 A,H1,1.E3,2.0) will create a source of first-phase enthalpy which is proportional to pressure squared; but: PATCH(*P1A,... ) followed by COVAL(*P1A,H1,1.E3,2.0) will not.
Patch-wise variables are those having a distinct value for each cell forming a patch which is created in the SATELLITE. These are stored in segments of the F-array having length equal to
(IXL-IXF+1)*(IYL-IYF+1)*(IZL-IZF+1)
for each patch, one such segment being supplied for each PWV.
The integer names are those which appear in COMMON block /LBPV/ of GRDLOC, which is as follows:
COMMON/LBPV/PVGENR,PVDISS,PVSKIN,PVRLVL,PVSTRS,PVRCDS,PVSTAN,
1 PVMASS,PVVMAS,PVURES,PVVRES,PVWRES,PVMAS2,PVCO,PVCP,
1 PVVMS2,PVURS2,PVVRS2,PVWRS2,PVSCAX,PVSCAY,PVSCAZ,PVYPLS,
1 LBPVSP(7)
From this it can be deduced that space has been provided for 30 patch-wise variables, that the first 23 names have been allocated (but could be changed) and that the last 7 are spares.
The meanings of the 23 allocated names are:-
PVGENR, (generation rate-dissipation rate) of turbulence energy;
PVDISS, generation rate of turbulence energy;
PVSKIN, the "skin-friction" coefficient;
PVRLVL, the relative velocity;
PVSTRS, the wall shear stress divided by density;
PVRCDS, the reciprocal of the wall distance;
PVSTAN, the Stanton number;
PVMASS, the first-phase mass flux;
PVVMAS, the GROUND-set "value" associated with first-phase mass input;
PVURES, the x-direction first-phase velocity resolute;
PVVRES, the y-direction first-phase velocity resolute;
PVWRES, the z-direction first-phase velocity resolute;
PVMAS2, as for PVMASS, but for the second phase;
PVCO, skin-friction factor;
PVCP, pressure coefficient;
PVVMS2, PVURS2, PVVRS2, PVWRS2, PVSCAX, PVSCAY, PVSCAZ, PVYPLS, the normalised wall distance, yplus.
The remainder are spares, which users can employ for their own purposes.
The arguments of the PATCH and COVAL commands are also stored, as single values, in the F-array, whether they are integers or reals.
wbs