# nut and nuTilda in simpleFoam

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 August 7, 2014, 15:02 nut and nuTilda in simpleFoam #1 Member   Michael Kruger Join Date: Jul 2014 Location: South Africa Posts: 38 Rep Power: 3 What are the differences between nut and nuTilda in the simpleFoam solver? In the PitzDaily simpleFoam tutorial, both nut and nuTilda are set to zero, does this mean the problem is modelled as inviscid? In the airFoil2D tutorial both nut and nuTilda are given values of 0.14 m^2/s. I believe the kinematic viscosity of air at room temp is about 15.11e-6 m^2/s, where in the world does the value of 0.14 m^2/s come from?? Is it perhaps because of a scaling factor introduced somewhere? Any clarification on the subject will be greatly appreciated. Thank you in advance.

 August 8, 2014, 03:33 #2 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,274 Rep Power: 18 Hi Michael, The files you are refering to provide boundary and initial values for the turbulent viscosity. (That's why it is "nut" and not just "nu"). Depending on the turbulence model you use they have different names. I don't know the airFoil2D tutorial, so I don't know which turbulence model it uses and thus which of the files is actualy needed. The fastes way is just to delete both files and start the solver. It will tell you the name of the files that are needed to run. "Nutilda" comes from the Spalart-Allmaras model, where "nut" is transformed to "nuTilda" and the model equation is solved for nuTilda. Anyway, if you set the value to zero in these files it just means that the initial value is zero. If you don't get convergence you can try other values, such as "0.14m^2/s" in the tutorial. The viscosity of air is set in a different file (constant/transportProperties) and should match the value you wrote. Philipp. __________________ The skeleton ran out of shampoo in the shower.

 August 8, 2014, 03:38 #3 Member   Michael Kruger Join Date: Jul 2014 Location: South Africa Posts: 38 Rep Power: 3 Excellent thank you Phillipp, that solves my problem. Might you be able to help be with this question: Running a solver from a case directory stored anywhere? Thank you in advance. __________________ ------------------------------------------------------- Michael

 Tags nut nutilda, simplefoam, solvers

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