Mesh not refined enough at the wall

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farina_m
Posts: 2
Joined: Thu Nov 29, 2018 4:20 pm

Mesh not refined enough at the wall

Post by farina_m »

Hello,

we tried to compute the flow through a dialysis tube, which always worked out with a earlier version of Code_Saturne. Now we are working with Code Saturne 3.0.0 and we do not get the correct results anymore.
In the listing file we get errors, which state:
"WARNING: MESH NOT REFINED ENOUGH AT THE WALL"
Furthermore the mass continuity is not given, so the velocities at the inlet and outlet of the mesh are not the same. We thought it is due to the computation of a turbulent flow with a steady, laminar flow. But even by defining a finer mesh and by decreasing the velocity so that we get a Reynolds number of a laminar flow, we were not able to generate the right results.
Is there a way to solve the problem and get the corect results?

Thank you and best regards,
Farina
Attachments
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setup.log
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listing.log
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Luciano Garelli
Posts: 280
Joined: Fri Dec 04, 2015 1:42 pm

Re: Mesh not refined enough at the wall

Post by Luciano Garelli »

Hello,

I think that the first recommendation is to switch to a newer version of CS, the code has been improved and bug has been corrected. You are running a version of 2013.

With respect to your question in the second time step you have a Y+=19 and a Courant of 237. You are running the case with no turbulence model (laminar), so a limit value of Y+ for the viscous sublayer is set to 2.381, if this limit is exceed you get the warning.

Also, the definition of the reference time step is to high (Courant of 237). Did you do some preliminary estimation of the reference time step for a Co=1? Using the mesh size and an average velocity. In a first attempt I will try to reduce the time step almost two orders.

Regards,

Luciano
farina_m
Posts: 2
Joined: Thu Nov 29, 2018 4:20 pm

Re: Mesh not refined enough at the wall

Post by farina_m »

Hello,

thank you for the quick response. I'm a student and I am going to ask my professor to update the CS version.
I did not do a preliminary estimation yet and I will definitely try to run the calculation with a reduced time step.

Thank you for your help,
Farina
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