|May 6, 2014, 04:43||
Wrong velocity profile in pipe
Join Date: Apr 2014
Posts: 3Rep Power: 4
I am a beginner with OpenFoam and I am stuck with a problem here. I am trying to run non Newtonian flow in a pipe and I have got strange results ;
I did a 5 degree piece of a pipe with wedge condition. I know the mesh seems bad but I don't think that it is the problem here. My probleme is the following ;
For the first iterations, I have a velocity profile with 0 on the axis and on the wall (fig U_it100_5degree_pipe). Resulting a low shear rate at half radius (fig shearRate_it100_5degree_pipe) and so very high viscosity values (fig nonNewtonian_it100) since a power law is used. The more the computation runs, the more this high viscosity region goes to the axis and get stabilized (fig nonNewtonian_it60000). I need a lot of iterations to converged (60000). I did the same for a full pipe (fig mesh_full_pipe) and 2000 iterations where enough to converged and I didn't have a zero velocity at the axis for the first iterations.
My question is ;
The profile I get for the first iterations, is it due to ;
- a bad mesh ? I have tried several and in the end the probleme is still here but can be lowered.
- periodic condition ? I used wedge, cyclic and cyclicAMI and it didn't change my problem. As I have a one mesh case in y direction, in the end it's normal it doesn't change anything, right ?
- the "empty" condition on the axis that could induce a 0 velocity for the first iterations ?
Many thanks for your help,
link to figures and input files :
|pipe, profile, velocity|
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