[ce73stargazer]

Hi there

Just for my own study purpose I created a simple mesh with 2 cell in the x direction and 3 layers in y direction. (shown in the scratch).

The numbers written in the scratch show the face number in the face file, however when i checked the owner and neighbour file,I dont understand whats the number in the main body stayed for, anyone have some suggestion?

The owner file shows

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.4.1 |
| \\ / A nd | Web: http://www.openfoam.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/

FoamFile
{
version 2.0;
format ascii;
instance "constant";
local "polyMesh";
object owner;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


29
(
0
2
4
0
2
1
3
0
1
2
3
4
5
0
1
2
3
4
5
0
2
4
1
3
5
0
1
4
5
)


// ************************************************** *********************** //

and the neighbour shows

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.4.1 |
| \\ / A nd | Web: http://www.openfoam.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/

FoamFile
{
version 2.0;
format ascii;
instance "constant";
local "polyMesh";
object neighbour;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


29
(
1 //0
3 //1
5 //2
2 //3
4 //4
3 //5
5 //6
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
-1
)


// ************************************************** *********************** //

[ce73stargazer]

For those who still interested in the answer.

I kind figured it out myself. So basically, the owner file, it's the cell ID file for those faces belongs to which cell.

For example the first face (face 0) in the face file (first value) belongs to cell 0 (first value in the owner file), the second face (face 1) belongs to cell 2 and so on.

Similarly for the neighbours are for these cells with a shared faced.

[pvpnrao]

Hi

Do you know how OpenFOAM decides which cell is owner and which one is neighbor.

Or the logic with which the indices are decided?

[ce73stargazer]

Originally Posted by pvpnrao

Hi

Do you know how OpenFOAM decides which cell is owner and which one is neighbor.

Or the logic with which the indices are decided?

Hi there, if i am not mistaken, I believe that a face is belonging to the cell at the negative direction and neighbour for the cell at positive direction.
For example the case i have there, for face 0, is belong to cell 0 (top left cell)( negative x diretcion)and neighbour to cell 1 (top right cell) (positive x direction).
You can build a simple 2X2X2 cube to check, which should be right

[Nik P.]

Hi,
OpenFOAM notation in polyMesh folder is obviously not meant to be human-readable I am dealing with the same subject. Although the thread is quite old, I add a few remarks:
Thank you for the explanation in second post, @ce73stargazer!

Hi there, if i am not mistaken, I believe that a face is belonging to the cell at the negative direction and neighbour for the cell at positive direction.
For example the case i have there, for face 0, is belong to cell 0 (top left cell)( negative x diretcion)and neighbour to cell 1 (top right cell) (positive x direction).
You can build a simple 2X2X2 cube to check, which should be right

I did not check, but I think this cannot hold for arbitrary meshes, e.g. using tetrahedron. The sign of the direction is not unique if the face is not parallel to a coordinate plane. So the definition in code surely is more complicated than that.


This is probably a bit off-topic, but I was very glad to find the following utility which might also help to understanding polyMesh-information: https://www.openfoam.com/documentati...llCentres.html

[harshabose]

Yes. You are right . A face is shared by two cells and if the face vector is pointing away from, let say Cell A, then Cell A is the owner and the other is neighbour.
In more technical words, the cell which gets positive flux is neighbour and the one giving is the owner. I found a great image depicting this:
https://imgur.com/jb8sOs4

In few case, this might not hold true. Such as in boundary or "non-internal" faces, the owner cell is the cell which the face shares and the neighbour is just kept as "-1" (optional to include in the neighbour file). In boundary conditions such as periodic or symmetry, the neighbour cells are the appropriate ghosts cells.