Divergence ?

[bachlinh]

Hello everyone,

I have simulated the convection coupled to radiation in a symmetry geometry.
At the end of simulation time, the time evolution of variables remains unchanged.
But when i visualized the results, i havenot found the symmetry field as expected.

Does it means that my solution divergences ?
If yes, can you suggest some reasons ?

Thank you,

[Yvan Fournier]

Hello,

When a simulation diverges, it usually crashes, so if quantities are not evolving anymore, it has probably converged to a wrong solution. With the information provided, I cannot guess more.

Regards,

Yvan

[bachlinh]

Thank you

[bachlinh]

Hello ,

In more details, my simulations were the coupling of double diffusive convection and gas radiation at different optical thicknesses. And in all considered cases, only one value of the optical thickness gives this strange behavior.

My configuration is a cubic cavity with a small obstacle (heat and pollutant source) on its floor. The top and bottom of the enclosure are adiabatic and impermeable while the vertical walls are set at a smaller temperature than that of the obstacle.
The Ra is about 5E6, Pr = 0.71, Le = 1.2.

What is the information that you need to give a guess for my situation ?

Regards,

[Yvan Fournier]

Hello,

The forum usage recommendations list the info which can be useful.

Regards,

Yvan

[bachlinh]

Hello,

I used the Code Saturne v5.0.8.
I attach here the files from my simulation.
Please read them and give me a guess about my situation.
However, i cannot upload the listing file.

Regards,

[Yvan Fournier]

Hello,

You are still missing the main logs (listing and setup.log), so I am still missing most of the information.

The radiative solvers converge very fast (2 iterations, while in many moderately complex cases 15 or more is more typical), so I assume this may be due to an important optical thickness, but I am not sure.

Could you try also using the GUI rather than user subroutines (art least for testing) to see if you have the same sensitivity or if it might be a bug on that side (at least, test progressively as a form of bisection) ?

With only a small part of the recommended info that is all I can say.

Regards,

Yvan

[bachlinh]

Thank you very much for your reply,

I attach here the setup.log file and zipped listing file.

Actually, i used the GUI to enter the value of absorption coefficient. But i will try your suggest.

Regards,

[Yvan Fournier]

Hello,

I did not notice anything strange in the logs, so this definitely seems to be in the "unexpected results" category rather than a divergence type problem.

How far from expected results are you ? Do you have any views ? Did you try without user-defined subroutines in case you have an error there ?

Regards,

Yvan

[bachlinh]

Hello,

Here are the results without (symmetry) and with radiation.

Without radiation, the thermal field is symmety but consideration of gas radiation breaks it.

For accounting radiation, compared to the without case, i only modified the absorption coefficient in the GUI.

It seem this absorption coefficient is sensitive because when i enters another one (for a higher optical thickness), i got the symmetry solotions as expected.

The user subsoutines are only for the declaration of new variables and post processing.

Regards,