SimpleFoam nutilda an R
 

What are nutilda and R for when solving using simpleFoam?

nuTilda is the kinematic turbu
 

nuTilda is the kinematic turbulent viscosity

and R is the Reynolds Stress t
 

and R is the Reynolds Stress tensor.

Best regards,

Niels

Hey thanks for the quick reply
 

Hey thanks for the quick reply :-)

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??

Thank you in advance.

dino

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?
Please kindly advise.
Regards,
Ivan

Hi, all, In regards to bo
 

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

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.

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

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


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

Regards
Rishi

Hello,

an answer is given here

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

Markus

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?

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