[volker]

Hi,

I experienced a problem when using the post-processing utility R to evaluate the Reynolds stress tensor based on a compressible simulation using a kEpsilon turbulence model. The Reynolds stress tensor is needed as initialization for a RSM simulation.
The problem I experienced is basically related to the compressible nature of my simulation and it seems that the R-utility is written exclusively for incompressible flows (makes use of transportProperties file).
I searched already the forum without success.
Does anybody have a suggestion how to resolve that issue?


I'm happy about any idea.


Greets, Volker

[SD@TUB]

Hello Volker,

reading in Doxygen --> base class for incompressible turbulence models, i guess that R just work for incompressible turbulent calcualtions so far.

I tried some sampling with your mentioned tool and i'm a little confused, 'cause i get six columns for the reynolds stress tensor in my output file!
Could you/someone explain me the columns? In Doxygen i can't find the source of the utility R!
For future development of post-processing tools it would be useful to include an obvious header to the produced output files.


Regards,
/Stefan

[chegdan]

Originally Posted by SD@TUB

Hello Volker,

reading in Doxygen --> base class for incompressible turbulence models, i guess that R just work for incompressible turbulent calcualtions so far.

I tried some sampling with your mentioned tool and i'm a little confused, 'cause i get six columns for the reynolds stress tensor in my output file!
Could you/someone explain me the columns? In Doxygen i can't find the source of the utility R!
For future development of post-processing tools it would be useful to include an obvious header to the produced output files.


Regards,
/Stefan

I know this is old, but I thought I would answer anyway.

You only have 6 components because you have a symmetric tensor Rxx, Ryy, Rzz, Rxy, Rxz, Ryz. that means that Rxy=Ryx, Rxz=Rzx, and Ryz=Rzy.

[rajeshkunwar]

Hi Volker,

I am also facing the same problem while getting Reynolds stress. Did u solve this issue? If yes, please post the solution so that others can also get benefited.

Regards
Rajesh

[chegdan]

You can make a custom tool to calculate R for compressible cases. To create a compressible turbulence model you will need to read in:

    Info<< "Creating turbulence model\n" << endl;
    autoPtr<compressible::turbulenceModel> turbulence
    (
        compressible::turbulenceModel::New
        (
            rho,
            U,
            phi,
            thermo
        )
    );

So you will need a thermo object to pass to the constructor. Basically, you will have to look at a compressible solver (e.g. rhoPimpleFoam) and add things like a compressible phi, thermo from basiPsiThermo, etc. Most of these changes are in the createFields.H file in the R utility....but I suggest you make your own utility separately called something like "Rcompressible". Additioanlly, you will have to change some entries in the Make/Options file to let the compiler know where to search for these new "compressible" classes. Hope this helps.

[rajeshkunwar]

Thanks Mr. Daniel for your help.

I have created the utility for computing Reynolds stresses for compressible solver.

Regards
Rajesh

[charmc]

Dear Rajesh:
As a newer to openfoam ! Can you write more detail about how to creat the utility for computing Reynolds stresses for compressible solver ?
Thank you !

[flames]

Hello there,

In openfoam, what is the order of the components in Reynolds stress tensor? For example, the Reynolds stress is (1,2, 3, 4, 5, 6), how these 6 components corresponds to the Rxx, Ryy ......? Thank you in advance!

flames

Originally Posted by chegdan

I know this is old, but I thought I would answer anyway.

You only have 6 components because you have a symmetric tensor Rxx, Ryy, Rzz, Rxy, Rxz, Ryz. that means that Rxy=Ryx, Rxz=Rzx, and Ryz=Rzy.

[johnkh]

Rxx, Rxy, Rxz, Ryy, Ryz and Rzz correspond to R(0), R(3), R(4), R(1), R(5) and R(2) respectively.

[maphd]

Hi,

I have a question: is there a way to read Reynolds stresses directly from Fluent? If you could help me on this, I really appreciate it.

Thanks,

[jensi_t]

Hey maphd,

you can use the fluentDataToFoam utility, but you have to adapt it bacause Reynolds Stresses are missing:

    //Reynolds stresses
    
    if (fields.found(128) || fields.found(129) || fields.found(130) || fields.found(131) || fields.found(132) || fields.found(133))
    {
        Info << "Converting reynolds-stresses field" << endl;
        volSymmTensorField R
        (
            IOobject
            (
                "R",
                mesh.time().timeName(),
                mesh,
                IOobject::NO_READ,
                IOobject::NO_WRITE
            ),
            mesh,
            dimensionedSymmTensor("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), symmTensor::zero)
        );

        if (fields.found(128))
        {
            R.replace
            (
                symmTensor::XX,
                fdc.convertField
                (
                    "UU",   // field name
                    128,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }

        if (fields.found(129))
        {
            R.replace
            (
                symmTensor::YY,
                fdc.convertField
                (
                    "VV",   // field name
                    129,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }
        
        if (fields.found(130))
        {
            R.replace
            (
                symmTensor::ZZ,
                fdc.convertField
                (
                    "WW",   // field name
                    130,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }
        
        if (fields.found(131))
        {
            R.replace
            (
                symmTensor::XY,
                fdc.convertField
                (
                    "UV",   // field name
                    131,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }
        
        if (fields.found(132))
        {
            R.replace
            (
                symmTensor::YZ,
                fdc.convertField
                (
                    "VW",   // field name
                    132,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }
        
        if (fields.found(133))
        {
            R.replace
            (
                symmTensor::XZ,
                fdc.convertField
                (
                    "UW",   // field name
                    133,           // fluent Unit number
                    dimensionedScalar("zero", dimensionSet(0, 2, -2, 0, 0, 0, 0), 0)
                )
            );
        }
        R.write();
    }

epsilon as well as i remember

        if (fields.found(6))
    {
        Info << "Converting dissipation rate field" << endl;
        fdc.convertField
        (
            "epsilon",   // field name
            6,     // fluent Unit number
            dimensionedScalar("zero", dimensionSet(0, 2, -3, 0, 0, 0, 0), 0)
        )().write();
    }

[canopus]

Thanks to JohnKhoo and to make it clear-

Output files obtained by executing R utility (and those obtained by running sample on it) list Reynolds stresses in order of

Rxx, Rxy, Rxz, Ryy, Ryz and Rzz

respectively.

and for viewing in paraview the same corresponds to

 R(0), R(3), R(4), R(1), R(5) and R(2)

respectively.

[abas.rahmani86]

hi guys
I want to know how i can extraction reynolds stress tensor from k-e model theorically?
tnx

[Jess80]

Hi,

know that k, the turbulent kinetic energy par unity of mass, can be calculated with
k=1/2 (U'x^2+U'y^2+U'z^2 ) where U'x, U'y and U'z are the fluctuating components of velocity in the x, y and z directions.
whereas R is a symmetric tensor with the following components:

Rxx Rxy Rxz
Rxy Ryy Ryz
Rxz Ryz Rzz

and with Rxx=U'x^2
Rxy=0 if isotropic turbulence (same in all directions), otherwise Rxy=Temporal Average (U’x*U’y)
Rxz=0 if isotropic turbulence (same in all directions) , otherwise Rxz=Temporal Average (U’x*U’z)
Ryy=U'y^2
Ryz=0 if isotropic turbulence (same in all directions), otherwise Ryz=Temporal Average (U’y*U’z)
Rzz=U'z^2

If Rxy=Rxz=Ryz=0, k=0.5*(Rxx+Ryy+Rzz)

The other way around you have to make the assumption that turbulence is isotropic, that is Rxx=Ryy=Rzz and Rxy=Rxz=Ryz=0 and therefore Rxx=2k/3.

Hope this helps.

[Jess80]

After searching the OpenFOAM code, I finally found the piece of code that indicates how R is calculated.
It is in the file named eddyViscosity.C and can be consulted at this link: https://www.openfoam.com/documentati...8C_source.html

At line 117: ((2.0/3.0)*I)*tk() - (nut_)*dev(twoSymm(fvc::grad(this->U_)))

When calculating R with the k- ε model, the code for the calculation of the value of nut can be found in kEpsilon.C, line 42 (https://www.openfoam.com/documentati...8C_source.html)

this->nut_ = Cmu_*sqr(k_)/epsilon_;

[Marcio]

Hey guys,

after searching for the Order of the Reynolds Stress file R in OF to compare wirh ParaView I found a switcheroo in the last posts. I mean this post explicitly:

Output files obtained by executing R utility (and those obtained by running sample on it) list Reynolds stresses in order of

Code:

Rxx, Rxy, Rxz, Ryy, Ryz and Rzz

respectively.

and for viewing in paraview the same corresponds to

Code:

R(0), R(3), R(4), R(1), R(5) and R(2)

respectively.

Can somebody else confirm it? The order I saw comparing OF 5.0 and ParaView 5.6 is following:

Rxx , Rxy , Rxz , Ryy , Ryz and Rzz |OpenFoam
R(0), R(3), R(5), R(1), R(4) and R(2) |ParaView


I used the Calculator to extract the Scalar-values for every R-value and compared it to a corresponding line in the turbulenceProperties_R-file

[FoamingSimon]

Originally Posted by Marcio

Hey guys,

after searching for the Order of the Reynolds Stress file R in OF to compare wirh ParaView I found a switcheroo in the last posts. I mean this post explicitly:

Can somebody else confirm it? The order I saw comparing OF 5.0 and ParaView 5.6 is following:

Rxx , Rxy , Rxz , Ryy , Ryz and Rzz |OpenFoam
R(0), R(3), R(5), R(1), R(4) and R(2) |ParaView


I used the Calculator to extract the Scalar-values for every R-value and compared it to a corresponding line in the turbulenceProperties_R-file

I get the same results, using OF 7 and Paraview 5.6.0, when extracting data and comparing these with Paraview plots.

[randolph]

Originally Posted by FoamingSimon

I get the same results, using OF 7 and Paraview 5.6.0, when extracting data and comparing these with Paraview plots.

Seems legit with OpenFOAM v1912 and Paraview 5.6.3

[ARG]

Originally Posted by FoamingSimon

I get the same results, using OF 7 and Paraview 5.6.0, when extracting data and comparing these with Paraview plots.

Seems to be true for OpenFOAM2312 and ParaView 5.12.0-RC3