Sequence of data values for UPrime2Mean
 

Hello,

The fieldAverage funtionObject can be used to write out prime2Mean values for the velocity field. A section of the resulting output file (UPrime2Mean) is shown below (from the pitzDaily example employing LES):

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volSymmTensorField;
location "0.001";
object UPrime2Mean;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 2 -2 0 0 0 0];


internalField nonuniform List<symmTensor>
12225
(
(0.797714 0.015699 0 0.00107185 0 0)
(0.0880994 -0.00361673 0 0.000736635 0 0)
(0.167389 -0.00701045 0 0.000363688 0 0)

Can you please direct me to the documentation which tells me how the precise components for the 6 values of the symmetric tensor <u'_i u'_k> are arranged? I can well imagine that the first and last are <u'_x u'_x> and <u'_z u'_z>, but I want to be certain about the rest in between.

There is a post from 2015 which asks the same question (see link below):

https://www.cfd-online.com/Forums/op...ime2means.html

I don't disagree with the response provided in the cited post, but I just want to be sure about where this information is coming from. I felt I should post a new thread because the one from 2015 may be too old.

In particular, the response in the post from 2015 suggests: "You can check by using foamCalc components UPrime2Mean and compare to your tensor."

I would like to verify too, but I have two issues: 1) I am not finding many helpful sources on how to use foamCalc (i.e. I have no idea how to use foamCalc), 2) my openFOAM installation (v1912) doesn't even seem to have the foamCalc utility.

So, my request is two-fold:

Source for confirming that the sequence of 6 numbers in the file UPrime2Mean is given by UPrime2Meanxx UPrime2Meanxy UPrime2Meanxz UPrime2Meanyy UPrime2Meanyz UPrime2Meanzz.

And, how to verifiy this with a utility that can be applied to the UPrime2Mean field.

Many thanks for your help.

To my knowledge:

Any symmetric tensor, e.g. the Reynolds stress tensor components are in this order: (Rxx Rxy Rxz Ryy Ryz Rzz) or, using a different notation: (u'^2 u'v' u'w' v'^2 v'w' w'^2).

HPE,

Thank you for your response. I agree that the order you suggest makes sense. But, we are talking about how something has been implemented in software. There must be a section of code, or documentation which confirms this, at the very least. And, to the second part of my question, how can it be verified?
I have found this other post which confirms the sequence you and the post in 2015 I cite in my first message refer to:

https://www.cfd-online.com/Forums/op...ome-grids.html

I can confirm the following sequence of UPrime2Mean.


OpenFOAM (v1912):

1. Rxx
2. Rxy
3. Rxz
4. Ryy
4. Ryz
6. Rzz


ParaView:

1. Rxx
2. Ryy
3. Rzz
4. Rxy
4. Ryz
6. Rxz


I checked it doing the following:

Write the UPrime2Mean field by using a fieldAverage function in the controlDict.I opened the solution with Paraview and choose the calculator filter. Next selected attribute type: cell data.
Result array name e.g. result
Select scalars e.g. UPrime2Mean_XX _YY and so on.

Open a spread sheet view and compare the value with your OpenFoam solution file.

Thank you for sharing that.