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-   -   SimpleFoam nutilda an R (http://www.cfd-online.com/Forums/openfoam-solving/60684-simplefoam-nutilda-r.html)

 linnemann May 26, 2008 04:41

SimpleFoam nutilda an R

What are nutilda and R for when solving using simpleFoam?

 danie May 26, 2008 04:52

nuTilda is the kinematic turbu

nuTilda is the kinematic turbulent viscosity

 ngj May 26, 2008 05:12

and R is the Reynolds Stress t

and R is the Reynolds Stress tensor.

Best regards,

Niels

 linnemann May 26, 2008 07:18

Hey thanks for the quick reply

Hey thanks for the quick reply :-)

 dinonettis May 26, 2008 16:30

Hi everybody! concerning R

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??

dino

 ivanwhlau August 17, 2008 10:55

Hi, I am running a k-eps

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?
Regards,
Ivan

 ivanwhlau August 17, 2008 11:07

Hi, all, In regards to bo

Hi, all,
In regards to boundary conditions, besides inlet,
I have the following: outlet, wall, ground, external
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 August 18, 2008 05:57

You only have to set the field

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 August 18, 2008 06:14

Thanks a lot, Eugene.

Thanks a lot, Eugene.

Hi openfomers, I am trying to

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 March 13, 2009 06:22

HI Gerard, I dont know the

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

Regards
Rishi

 markusrehm January 18, 2011 04:08

Hello,

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

Markus

 alyucel October 8, 2014 12:14

Quote:
 Originally Posted by dinonettis (Post 196319) 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 October 9, 2014 08:14

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

Code:

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

```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()         )     ); }```

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