[linnemann]

What are nutilda and R for when solving using simpleFoam?

[danie]

nuTilda is the kinematic turbulent viscosity

[ngj]

and R is the Reynolds Stress tensor.

Best regards,

Niels

[linnemann]

Hey thanks for the quick reply :-)

[dinonettis]

Hi everybody!

concerning R and nutilda I would like to know something more as well!!
-First of all, should I iniatilize them with a value different from 0??
-Second, in simpleFoam when I use the k-epsilon model I've read on this forum that they are not necessary. Why??

Thank you in advance.

dino

[ivanwhlau]

Hi,
I am running a k-epsilon RNG model (simepleFoam).
turbulent, incompressible air flow around a rectangular low rise 3D building
I have set the following initial values of inlet:
U
k=1/2(UI)^2
epsilon=Cmu^0.75*k^1.5/l
nuTilda=Cmu&K^2/epsilon (is it correct?)
Do I need to set the value of R (currently, zeros)? If so, what should that be?
Please kindly advise.
Regards,
Ivan

[ivanwhlau]

Hi, all,
In regards to boundary conditions, besides inlet,
I have the following: outlet, wall, ground, external
zeroGradient for every parameters
U=0,0,0 at wall & ground
p=0 at outlet
Should I set k as zero at wall?
Re~=10^5
Pleas kindly help.
Regards,
Ivan

[eugene]

You only have to set the fields used by your solver/model. nuTilda and R are not used by the RNG model. For high-Re models k at the wall is normally set to zero gradient.

[ivanwhlau]

Thanks a lot, Eugene.

[gerado]

Hi openfomers,
I am trying to understand the implementation of simpleFoam but I have a problem with nuTilda.
can someone tell me the difference between nut and nuTilda ?


Regards

Gerard

[hellorishi]

HI Gerard,

I dont know the details, however I am also interested.

Just a clue: check the C++ documentation:
http://foam.sourceforge.net/doc/Doxygen/html/incompressible_2kEpsilon_2kEpsilon_ 8C-source.html

00120 nut_(Cmu_*sqr(k_)/(epsilon_ + epsilonSmall_))

and some details...
http://foam.sourceforge.net/doc/Doxygen/html/classFoam_1_1incompressible_1_1RASM odel.html


Yet to read it completely. Post here if you find answers to your questions.

Regards
Rishi

[markusrehm]

Hello,

an answer is given here

http://www.cfd-online.com/Forums/ope...t-nutilda.html

Markus

[alyucel]

Originally Posted by dinonettis

Hi everybody!

concerning R and nutilda I would like to know something more as well!!
-First of all, should I iniatilize them with a value different from 0??
-Second, in simpleFoam when I use the k-epsilon model I've read on this forum that they are not necessary. Why??

Thank you in advance.

dino

i'am wondering too

Second, in simpleFoam when I use the k-epsilon model I've read on this forum that they are not necessary. Why??

and where is using openFoam R and nuTilda?

[Tobi]

Hello,

• nut is not necessary to declar if you want standard settings. OpenFOAM sets up your nuTilda -> nut itselfs and you will get this field in every saved iteration step.
• R is not necessary anymore

Source code:
$FOAM_SRC/turbulenceModel/incompressible/ras/kEpsilon

    nut_
    (
        IOobject
        (
            "nut",
            runTime_.timeName(),
            mesh_,
            IOobject::NO_READ,
            IOobject::AUTO_WRITE
        ),
        autoCreateNut("nut", mesh_)
    )

tmp<volSymmTensorField> kEpsilon::R() const
{
    return tmp<volSymmTensorField>
    (
        new volSymmTensorField
        (
            IOobject
            (
                "R",
                runTime_.timeName(),
                mesh_,
                IOobject::NO_READ,
                IOobject::NO_WRITE
            ),
            ((2.0/3.0)*I)*k_ - nut_*twoSymm(fvc::grad(U_)),
            k_.boundaryField().types()
        )
    );
}