# SimpleFoam nutilda an R

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 May 26, 2008, 04:41 What are nutilda and R for whe #1 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 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 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 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 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 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 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 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 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 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 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 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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