Encyclopaedia Index

### Z

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The Z component.

### Z

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Once activated, GRID, VECTOR, CONTOURS and SURFACE will be plotted on each Z 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.

### Z

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

### Z-dependent properties

Z-DEPENDENT properties When setting a property in GROUND as an IZ-dependent function, the user need not concern himself with the question of whether the current- or high-slab value is being computed. EARTH looks after this matter.

### Z-direction diffusion coeff., proportion of

(see ZDIFAC real, Group 8)

### Z-direction in 1- or 2-dimensional problems

To use the z-direction in a one- or two-dimensional problem usually increases the computer time, as compared with using the x- or y-direction; but it increases the fineness of grid which may be used with a computer of given size. It is the built-in out-of-core facility of PHOENICS which brings the latter advantage.

### Z-direction, setting coordinates of

(see ZFRAC real array, Group 5)

### Z-length of domain, specifying the

(see ZWLAST real, Group 5)

### Z-wise variables

See PHENC: X-wise variables

### Z-wise moving grid, specification of

(see ZMOVE real flag, Group 19)

### ZC

---- PIL real Array; Group 6 ----------------

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

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

### ZCEN

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

### ZDIFAC

---- PIL real; default= 1.0; group 8 --- -

ZDIFAC....proportion of z-direction diffusion coefficient added to the denominator of the finite-volume correction equation when the whole-field solver is not used. Positive values less than 1.0 may accelerate convergence when z-direction diffusion is strong.

Since this acts only on a coefficient of the correction equation, it does not affect the final solution but only the speed with which the solution is reached.

### ZF

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

### ZFRAC

----- PIL real array; default=100*1.0; -

ZFRAC....Array for use in setting the z-direction coordinates of the "high" faces of the computational cells used for the balances of all variables except (for NZ greater than 1) z-direction velocity components W1 and W2.

Distances are measured from the low-z (i.e.extreme low) boundary of the flow domain.

ZFRAC values may be set indirectly by means of the commands GRDPWR,SUBGRD or by one of the two other methods described for TFRAC.

### ZGNZ

ZGNZ 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 of the centres of the continuity cells from the z=0.0 plane. The array is accessed via GETZ and holds values for all IZ.

### ZL

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[ZL] specifies the last K index of the current plotting region. The default value is NZ+1 for GRID and NZ for other plotting elements.

### ZMOVE

----- PIL real flag; value= -10230.0; -

ZMOVE...Set W1AD= ZMOVE in order to inform EARTH that the z-wise moving-grid option is to be used.

This moving-grid option permits the z-wise grid to be sub-divided into any number of parts ( up to NZ ), which may be specified as stationary, moving and expanding or contracting, by way of subroutine GXPIST in section 1 of group 19 of GROUND.

Subroutine GXPIST called from GREX supplies an example of a 2-part grid suited to piston-in-cylinder calculations. The control parameters for this option are: IZW1, AZW1, BZW1 and CZW1. GXPIST presumes that the settings of the grid distribution by ZFRAC are for the grid when the piston is at bottom dead centre.

The following diagram depicts a 3-part grid suited to piston-in-cylinder calculations when the cylinder head has a cavity in it which requires a fixed grid:

```
1-------------->z
1
1        IZW(1)               IZW(2)          IZW(3)
1   :-------:--------------------:---------------:
1   :   1   :         2          :       3       :
1   :       :                    :               :
1   :-------:--------------------:---------------:
1        ZWO(1)                ZWO(2)         ZWO(3)   X
1                  O (= 'old', i.e. previous-time-step) ZW values
1
t    :-------:----------------------------:---------------:
1   :   1   :              2             :       3       :
1   :       :                            :               :
1   :-------:----------------------------:---------------:
1        ZWN(1)                       ZWN(2)          ZWN(3)
V                N (= 'new', i.e. current-time-step) ZW values
--------->---------------------------->--------------->
WAV(1)                       WAV(2)           WAV(3)
```

Part 1 of the grid, which contains the cylinder-head cavity is stationary.

Part 2 expands and contracts according to WAV(2), = d ZWN(2)/dt .

Part 3 m which contains the piston, which may have a bowl within it, moves with the velocity WAV(2) neither expanding nor contracting, provided that WAV(3) = WAV(2) .

### Zoom

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The image of the object in the current graphic window can be enlarged/shrunk with the mouse moving up/down.

### ZW

ZW is a Fortran real variable used in GROUND. It represents the z coordinate of the high face of the current slab. Being an item in the GRDLOC COMMON file, it may be accessed from GROUND files. However it possesses the correct value only from Group 19 section 4 onwards. It can be safely used in Groups 8, 9 and 13.

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

ZWADD....Addition which is made to z-coordinate values when these are used in some grid-stretching and other formulae in parabolic calculations, e.g. width increases as (zw+zwadd)**exponent.

See AZXU for more details.

### ZWLAST

---- PIL real; default=1.0; group 5 -----

ZWLAST....z-length of domain, with significance similar to those of XULAST and YVLAST.

### ZWNZ

ZWNZ 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 of the HIGH faces of the continuity cells from the z=0.0 plane. The array is accessed via GETZ and holds values for all IZ.

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