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Wrong velocity profile in pipe

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Old   May 6, 2014, 04:43
Default Wrong velocity profile in pipe
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Fredo
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Hello Foamers,

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,

Fredo.

link to figures and input files :
https://www.dropbox.com/sh/i4nyfyp3jgimktv/hTsgJTkypM
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