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-   FLUENT (https://www.cfd-online.com/Forums/fluent/)
-   -   Convergence (https://www.cfd-online.com/Forums/fluent/90281-convergence.html)

divergence June 19, 2017 08:33
Hmm... You are in a peculiar predicament here.

So just to be clear: you have a converged solution (residuals, monitors, maybe even animations point out in this direction) and you do not change any boundary conditions, models or URFs but saving files makes things go haywire?

Could you post some screen shots of your residuals and monitors here? There is probably something we have missed. What are your URFs? Is your mesh quality suitable for the task? Have you had an animation of flow field of your calculation? Maybe you are simply in a point of calculation where the next iteration simply gives a different result.

BlackHeartInertia June 19, 2017 08:46
Quote:
Originally Posted by divergence (Post 653948)
Hmm... You are in a peculiar predicament here.

So just to be clear: you have a converged solution (residuals, monitors, maybe even animations point out in this direction) and you do not change any boundary conditions, models or URFs but saving files makes things go haywire?

Could you post some screen shots of your residuals and monitors here? There is probably something we have missed. What are your URFs? Is your mesh quality suitable for the task? Have you had an animation of flow field of your calculation? Maybe you are simply in a point of calculation where the next iteration simply gives a different result.
The mass imbalance only change after doing more iterations

Sent from my SM-G570M using CFD Online Forum mobile app

BlackHeartInertia June 19, 2017 14:35
1 Attachment(s)
Quote:
Originally Posted by BlackHeartInertia (Post 653953)
The mass imbalance only change after doing more iterations

Sent from my SM-G570M using CFD Online Forum mobile app
Attachment 56800

I attached and image. I couldnt before because I wasnt near my computer. I hope never have that problem you said because that would be fatal. Thats another simulation with a lower temperature. Now Im still iteraring so I will see soon the new result for fluxes imbalances.

Ps. Good nick by the way

divergence June 20, 2017 01:27
Thanks for the pic. The calculation seems to be quite stable also in my opinion simply by evaluating the couple curves presented in the picture. Maybe you could try to lower the flow Courant number to 20 and the explicit relaxation factors for both momentum and pressure to 0.25. These default values usually -at least in my experience- have caused some instabilities in calculations. This depends naturally of the case itself.

Additionally, you might want to update your Fluent to a more modern version at some point :) Fluent has become much more robust after R14 version.

Oh, one more thing: I assume that the case where you took that screen shot had same kind of trouble with the saving and the mass balance. And I suppose that the current case has the same operational parameters.

BlackHeartInertia June 20, 2017 09:57
Quote:
Originally Posted by divergence (Post 654073)
Thanks for the pic. The calculation seems to be quite stable also in my opinion simply by evaluating the couple curves presented in the picture. Maybe you could try to lower the flow Courant number to 20 and the explicit relaxation factors for both momentum and pressure to 0.25. These default values usually -at least in my experience- have caused some instabilities in calculations. This depends naturally of the case itself.

Additionally, you might want to update your Fluent to a more modern version at some point :) Fluent has become much more robust after R14 version.

Oh, one more thing: I assume that the case where you took that screen shot had same kind of trouble with the saving and the mass balance. And I suppose that the current case has the same operational parameters.
Thank you very much for your comments helps a lot. I will take your advices and see what happend

waseeqsiddiqui June 26, 2018 11:05
Hi all,
I have a mesh of size 8 million. It converges the solution at 90 iterations. Energy, x, y, and z goes down to e-07, k and omega to e-05. My result in focus is CD and CL. The tolerance is changed for the latter two report def from e-03 to e-06. Still it converges at 90. LOL?

mahayheidari January 21, 2019 10:12
Apdl problem
 
Hello
I simulate a cylinder in ansys apdl
I have this error
solution not converged at time ansys apdl
Please help me

Pree1032 February 12, 2020 11:18
Quote:
Originally Posted by Centurion2011 (Post 314914)
I see all kind of mistakes on these forums when dealing with convergence, so I will give brief review of methods... :cool:

At convergence, the following should be satisfied:
  • All discrete conservation equations (momentum, energy, etc.) are obeyed in all cells to a specified tolerance OR the solution no longer changes with subsequent iterations.
  • Overall mass, momentum, energy, and scalar balances are achieved.
  • Monitoring convergence using residual history:
  • Generally, a decrease in residuals by three orders of magnitude indicates at least qualitative convergence. At this point, the major flow features should be established.
  • Scaled energy residual should decrease to 10-6 (for the pressure-based solver).
  • Scaled species residual may need to decrease to 10-5 to achieve species balance.
  • Monitoring quantitative convergence:
  • Monitor other relevant key variables/physical quantities for a confirmation.
  • Ensure that overall mass/heat/species conservation is satisfied.
Thank you a ton!:)

vivjk94 June 14, 2022 23:29
Quote:
Originally Posted by Centurion2011 (Post 339849)
There are training modules for Ansys, very useful. You can find them all over.

for example: http://avaxhome.ws/software/software..._training.html
This is a virus type of link. my antivirus blocked it


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