Encyclopaedia Index


---- Command; group 11 --------------

CONPOR....command used for setting a constant porosity over a patch.


The first argument specifies the base name used for the PATCHes generated. The name may be up to 8 characters long, but must be unique within the first five.

The second argument specifies the value of the constant: this will normally range from 0.0 to 1.0, but can exceed 1.0 when it is desired to expand the grid.

The third argument specifies by means of EAST, WEST, NORTH, SOUTH, HIGH, LOW which face of the cells in question the porosity value is to multiply, whereas CELL in argument 3 signifies that the porosity value is to multiply the cell volume.

The last 6 arguments of CONPOR determine which cells are in question according to ix-first, ix-last, iy-first, iy-last, iz-first, iz-last. If NREGX, NREGY, or NREGZ is greater than 1, the domain limits for CONPOR may be specified in terms of region numbers (see PATCH entry for details).

CONPOR also sets INIADD to F, so that the porosity settings made are not additive.

For further information, see the PHENC entry: CONPOR


(the command for defining a constant-porosity patch)

The above satellite-help entry describes the CONPOR command as it was originally introduced into PHOENICS. However, the command found further uses, and was augmented by further capabilities. The present article describes these, under the headings:

However, it should be mentioned that the once-popular setting:


as a means of representing the presence of solid obstacles to flow, is no longer necessary, and is best avoided.

Indeed, the Satellite of version 2.1.3 and later will replace settings of VPOR to zero, by settings of PRPS to 198.0, which corresponds to an anonymous solid, which is impervious to heat.

It is now best to use CONPOR only when some value other than 0.0 or 1.0 is to be set. The presence of solids is better handled directly, by way of PRPS.

What follows here is therefore mainly of historical interest.

(a) Omission of the name

If the first (ie NAME) argument of CONPOR is omitted, the PHOENICS SATELLITE will supply one, naming the patches as CMP0, CMP1, CMP3 etc in the order of their appearance in the Q1 file.

(b) Activation of wall friction

Although it has always been possible to introduce anywhere in the model the effect of wall friction, early users of the CONPOR command desired that they could be spared the necessity for introducing six wall patches for each block fow which CONPOR had set the volume porosity to zero.

For this reason, the CONPOR command was extended by the convention that, if NEGATIVE values were introduced for the IXF argument (say) then a wall-friction patch would be introduced for the WEST face of the block; and such patches would be correspondingly introduced on the EAST, SOUTH, NORTH, LOW and HIGH faces by making negative settings of IXL, IYF, IYL, IZF and IZL. Of course, the location of the block was influenced only by the absolute values of IXF, IXL etc.

This practice is still supported by PHOENICS version 2.1 for turbulent flow (signalled by a negative value of ENUT); but it has no influence for laminar flow, for which wall friction is the default conditions.

Should any user wish to switch wall friction OFF, for laminar flow, he must now do so by introducing a "GROUP-12" patch, of diffusion type, with a zero third argument in the relevant COVAL.

The advantages of the change of practice are:-

The current recommended practice is to avoid the use of negative IXF etc for turbulent flow also, by the simple expedient of setting = T the PIL variable EGWF, which stands for Earth-Generated Wall Functions (see PHENC entry of that name); for this causes EARTH to detect where a fluid adjoins a cell blocked by porosity or a true solid, and the take the necessary action to calculate the turbulence and the momentum transfers.

(c) Allowance for the presence of participating solids

When PHOENICS was first used for solving conjugate-heat-transfer problems, CONPOR was used to block the flow, without preventing the heat transfer, by the assignment of "value" to -1.0. Then the above- described wall-friction patches came into being, and associated heat-transfer boundary conditions; but the volume porosity remained at 1.0, so that the within-solid thermal processes could be simulated.

This practice had both conceptual and practical disadvantages, as compared with the currently recommended practice involving PRPS and EGWF=T. The conceptual puzzle was: If VPOR should really be 1.0, why set it to - 1.0? Indeed, what has porosity to do with the case anyway?

The practical disadvantage was that uncomfortably large numbers of patches were generated.

(d) Now-dispensed-with features

If the value is 0.0, and the third argument is CELL, the PHOENICS satellite has in the past created storage for cell-surface porosities and set these to zero at the faces of the zero-volume cells. Starting with version 2.1.2, this no longer occurs; for EARTH is able to detect the presence of the solid obstruction from the local value of VPOR, or (since version 2.1.3) PRPS.

(e) Examples of use

sets the porosity of the east faces of all the cells in the zone IX=2 to 5, IY=6 to 8, IZ=1 to 2 equal to 0.25 .