# k-epsilon model and simpleFoam

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 April 9, 2010, 08:32 k-epsilon model and simpleFoam #1 Senior Member   Join Date: Feb 2010 Posts: 213 Rep Power: 8 I have a few questions about model, I applied it to an airfoil (blade section of a marine propeller). I based myself on pitzDailyExptInlet tutorial. 1. why is turbulenceProperties file not included? 2. tutorial nut and nuTilda are set on zero. I used this configuration, is it correct? Here I read that nuTilda is superfluous, is it the same with nut? I'm confused, in tutorials fvschemes and fvSolution files I find nuTilda (and not nut). 3. in tutorial R file I read Code:  upperWall { type kqRWallFunction; } lowerWall { type kqRWallFunction; } why kqRWallFunction? Moreover, i had to add a value: Code: value uniform (0 0 0 0 0 0); is it correct? Last edited by vaina74; April 9, 2010 at 11:08.

 April 10, 2010, 03:27 #2 Member   matej forman Join Date: Mar 2009 Location: Brno, Czech Republic Posts: 91 Rep Power: 8 Hi, I got few answers for you: ad 2> nut is turbulent viscosity for incompressible flows, mut is dynamic turb. viscosity used for compressible or heat transfer flows. nuTilda is only for Spalart-Allmaras model. Therefore for k-eps model you need only nut or mut. try to remove all of them and the code will tell you which one is missing. in fvSchemes and fvsolution you need the variables accordingly The wall functions are defined here in sedction RAS wall functions ad 3> R is reynolds stress tensor and you do not need to set anything, look at \$FOAM/src/turbulenceModels/incompressible/RAS/kEpsilon/kEpsilon.C lines 140 to 160 and what you see is, that the R field is calculated internaly and is not read at all, so there is no point to set this file at all in your 0/ directory. good luck matej

April 12, 2010, 17:37
#3
Senior Member

Join Date: Feb 2010
Posts: 213
Rep Power: 8
Thank you, Matej. I already deleted nuTilda and all code lines in fvschemes and fvsolution. But I deleted
Code:
div((nuEff*dev(grad(U).T()))) Gauss linear;
too, so I had an error - I thought my case had no heat flow. Now it's ok. You're right about R (why was it in the 0 tutorial folder?), I deleted the relevant file and anyhow the code seems to work.

But i have still some questions, can anyone help me?

1. Why is turbulenceProperties file not included in pitzDailyExptInlet tutorial? I believed it was compulsory. Please, can you send me an example of an incompressible case?

2. I'm going to test different turbulent models on my 'hydrofoil'. I generated different meshes, such as to have 30 < y+ < 300 (I use near-wall functions). If yPlusRAS gives a bad output, I modify the mesh (generally too fine). With the model I have a problem: is always too low (about equal to 2-6). I'm afraid it depends on my setting files, maybe I adapted the pitzDailyExptInlet tutorial in a wrong way. Can you take a look at that (see attached file)?
Attached Files
 hydrofoil.tar.gz (59.5 KB, 31 views)

April 17, 2010, 14:18
#4
Senior Member

Join Date: Feb 2010
Posts: 213
Rep Power: 8
Please, help me. I'm in trouble with and simpleFoam. Lift and drag coefficients are enormous and too. I can't understand the problem, I refined and refined (and refined again) the mesh, but nothing really changed (and I use wall functions). I evaluated initial values for and as in ESI guidelines:

= 0.01
= 0.005

with

= 7.3 m/s
= 1%
= 1
and dynamic viscosity = 1.22e-3

I hadn't this terrible result with or Spalart-Allmaras turbulent models (obviously with different meshes), I can't understand that. Maybe it' a problem about my BC or fvSchemes and fvSolution files. Can anyone help me? See the attached files, please. I can't manage alone.
Attached Files
 hydrofoil.tar.gz (3.1 KB, 42 views)

 February 20, 2011, 13:36 #5 New Member   anonymous Join Date: Jun 2010 Posts: 2 Rep Power: 0 hi i didnt want to open a new topic so i state my question here. i am simulating a turbulent incompressible flow with simpleFoam and the kEpsilon model. i want to take a look at the Reynolds Stress Tensor. how can i make simplefoam to display it? i know that the tensor must be calculated and i would like to see the result regards //edit i found the function R wich calculations the reynolds stress tensor at a given time step. now i have an R file with the numbers, alot of numbers *g* thx anyway Last edited by masterfgee; February 20, 2011 at 14:51.

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