# Initialization of nut

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 September 25, 2020, 06:44 Initialization of nut #1 New Member   Lucie Recurt Join Date: Jun 2020 Posts: 17 Rep Power: 2 Hello! I want to run a k-epsilon simpleFoam simulation of a pipe but I got some questions: 1- in the tutorials, they initialize nut at 0 in the internal field and for every boundary. I don't really understand why because k and espilon are different of 0 and the approximation of nut is rho*Cmu*(k/eps) 2- do I have to use a calculator like this one: https://cfd-training.com/language/fr...de-turbulence/ to calculate epsilon and k's boundary condition or it doesn't give the value for the boundaries? Thank you in advance

 September 26, 2020, 11:13 #2 New Member   S A Join Date: Oct 2019 Posts: 7 Rep Power: 3 Those are just the initial conditions. It is indeed better and recommended to initialise them to non-zero values. You can find approximated values, as you said, from analytical formulas. From your Re, the turbulence intensity, k, eps, nut, etc.

 September 28, 2020, 10:55 #3 New Member   Lucie Recurt Join Date: Jun 2020 Posts: 17 Rep Power: 2 Internal field is just initial conditon but boundary conditions no... And I tried to put approximated values from analytical formulas but when I do that, I get a non-physical solution

 September 28, 2020, 17:56 #4 New Member   S A Join Date: Oct 2019 Posts: 7 Rep Power: 3 If your initial values are OK, you should check if the boundary conditions are ok. Also, check if your mesh is ok and even the size of the model (sometimes geometry files are in mm and we forget to apply a scaling when we mesh).

 September 30, 2020, 10:56 #6 New Member   Lucie Recurt Join Date: Jun 2020 Posts: 17 Rep Power: 2 Thank you for your answer Tobias! However one thing seems weird for me. How can OpenFoam calculate a value at the boundary? Because it has to be the last cell and cfd software use discretization to calculate a value in one cell. But at the boundary, there is not (n+1) cell...

 Tags boudary condition, epsilon, kepsilon, nut, openfoam