SimpleFoam nutilda an R

linnemann · May 26, 2008, 04:41

What are nutilda and R for when solving using simpleFoam?

danie · May 26, 2008, 04:52

nuTilda is the kinematic turbulent viscosity

ngj · May 26, 2008, 05:12

and R is the Reynolds Stress tensor.

Best regards,

Niels

linnemann · May 26, 2008, 07:18

Hey thanks for the quick reply :-)

dinonettis · May 26, 2008, 16:30

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 · August 17, 2008, 10:55

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 · August 17, 2008, 11:07

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 · August 18, 2008, 05:57

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.

gerado · March 9, 2009, 06:44

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 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 · January 18, 2011, 03:08

Hello,

an answer is given here

nut and nuTilda

Markus

May 26, 2008, 04:41	What are nutilda and R for whe	#1
linnemann Senior Member Niels Nielsen Join Date: Mar 2009 Location: Denmark Posts: 383 Rep Power: 10	What are nutilda and R for when solving using simpleFoam? __________________ Linnemann

May 26, 2008, 04:52	nuTilda is the kinematic turbu	#2
danie New Member Daniela Join Date: Mar 2009 Location: Italy Posts: 4 Rep Power: 6	nuTilda is the kinematic turbulent viscosity

May 26, 2008, 05:12	and R is the Reynolds Stress t	#3
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Posts: 1,158 Rep Power: 19	and R is the Reynolds Stress tensor. Best regards, Niels

May 26, 2008, 07:18	Hey thanks for the quick reply	#4
linnemann Senior Member Niels Nielsen Join Date: Mar 2009 Location: Denmark Posts: 383 Rep Power: 10	Hey thanks for the quick reply :-) __________________ Linnemann

May 26, 2008, 16:30	Hi everybody! concerning R	#5
dinonettis Member Leonardo Nettis Join Date: Mar 2009 Posts: 72 Rep Power: 6	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

August 17, 2008, 10:55	Hi, I am running a k-eps	#6
ivanwhlau Member Ivan Lau Join Date: Mar 2009 Location: Hong Kong Posts: 56 Rep Power: 6	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

August 17, 2008, 11:07	Hi, all, In regards to bo	#7
ivanwhlau Member Ivan Lau Join Date: Mar 2009 Location: Hong Kong Posts: 56 Rep Power: 6	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

August 18, 2008, 05:57	You only have to set the field	#8
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 724 Rep Power: 10	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.

August 18, 2008, 06:14	Thanks a lot, Eugene.	#9
ivanwhlau Member Ivan Lau Join Date: Mar 2009 Location: Hong Kong Posts: 56 Rep Power: 6	Thanks a lot, Eugene.

March 9, 2009, 06:44	Hi openfomers, I am trying to	#10
gerado New Member Gerard Mouokue Join Date: Mar 2009 Location: Darmstadt, Hessen, Germany Posts: 16 Rep Power: 6	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

March 13, 2009, 06:22	HI Gerard, I dont know the	#11
hellorishi Senior Member Rishi . Join Date: Mar 2009 Posts: 122 Rep Power: 6	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

January 18, 2011, 03:08		#12
markusrehm Senior Member Markus Rehm Join Date: Mar 2009 Location: Erlangen (Germany) Posts: 155 Rep Power: 6	Hello, an answer is given here nut and nuTilda Markus

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