How to initialize k and epsilon values?
I have been using OpenFoam and ANSYS Fluent simultaneously, and it seems the initial values of the k-epsilon model calculated by ANSYS are different from what I calculated, so I do not know whether I got the calculation correctly or not. Here is my settings:
I am trying to do an external flow like the motorBike tutorials, just by replacing the motorBike geometry by my own model. The parameters of my simulation: Freestream = 12.5m/s characteristic length (L) = 1.638m (I use the total length of my geometry as the characteristic length. Not sure if it is correct) Fluid : air Reynolds number = uL/v = (12.5)(1.638)/(1.5e-5) = 1365000 kinematic viscosity = 1.5e-5m^2/s Turbulence intensity level = 0.16*(Re^(-1/8)) = 2.7637% Turbulence length scale = 0.07L = 0.11466m By substituting the values into the calculation tools in cfd online (https://www.cfd-online.com/Tools/turbulence.php), I got: k = 0.17554J/kg e = 0.057727J/kgs However, from ANSYS Fluent: k = 0.24954J/kg e = 2.2404J/kgs It seems that either set of values are desperately wrong. May I know if I got my own calculation correctly? Help tell me if I did anything wrong! Thank you very much!! |
Hi Joe,
You could run the simulation without the obstacle and check the values of k and e at the outlet. Doing that you will know equilibrium values of k and e. This kind of verification is recommended for CFD wind studies. Best Regards, Paulo |
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I do not have a solid background on CFD, so please forgive for me ignorance. Thanks. |
The values from k, e calculation you entered in BCs are initial guess.
And usually L is height (orthogonal to freestream direction). |
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