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divergence detected in AMG solver ?

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Old   February 24, 2010, 12:54
Post divergence detected in AMG solver ?
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Hi everyone,

in some cases that I have runned before, the case started normally to converge and suddenly it stoped writing the message:
divergence detected in AMG solver: pressure

what this the reason and where is the problem ? who should I process to solve that

thanks
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Old   March 23, 2010, 07:00
Default divergence detected in AMG solver: pressure correction
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Hi all,

I am encountering this error when I compute my problem

divergence detected in AMG solver: pressure correction

My problem is 3D, supersonic (Mach=2.49); Flow over a conical probe; structured mesh;

I first used Spalart Almaras model for turbulence; it gave me the divergence error; So i used k epsilon; again I get the same error;

I declared all the outer boundary to be pressure far field; So there is no pressure outlet or velocity inlet as such;

The flow is compressible; unsteady

In the materials window; can I use viscosity to be constant; i used ideal gas for density;


Please let me know how to get rid of this error.

Reply asap!!

Thanks.
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Old   March 25, 2010, 19:47
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Hi
are u using steady or unsteady solver ?
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Old   March 25, 2010, 21:05
Default divergence amg solver
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unsteady solver; spalart almaras model; five stage runge kutta time stepping scheme
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Old   March 26, 2010, 02:51
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u can try to change ure pressure interpolation scheme. This can help.
However, the best way to avoid this is to reduce ure time step and to Reduce also the under-relaxation factors , specially if u have a transitional case ( iwhen u get a steady state, u can tolerate bigger time step, but this is not ure case as ure flow is supersonic).
If u care for precision, use more than one iteration by time step (as u reduce under-relaxation factors, the solution will converge more slowly): monitor data so u can estimate the number of iterations by time-step that u need.
Dont forget to ative the autosave command, so in ase that ure solution diverge, u dont loose everything.
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Old   March 26, 2010, 14:20
Default autosave command
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thank you very much for the help. I will try doin that; but please tell me how to activate the autosave command; if i do this, then how does fluent know how often to save the computation. let me knoe kindly!

Thanks.
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Old   March 26, 2010, 18:45
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Hi again
File--->write--->autosave
then u can choose saving frequency
Regards
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Old   March 26, 2010, 19:08
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Thanks you very much. So the frequency parameter determines how many seconds for which the computation has been saved.

I hope I am right! Let me know.

Thanks.
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Old   March 27, 2010, 07:07
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yes
if u dont change simulation parameters, u just need to save data files (without case files)
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Old   March 27, 2010, 07:14
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Thanks. I got you.
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Old   March 29, 2010, 15:57
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I am modeling supersonic flow over a probe. I am using the axis boundary condition in gambit for my axisymmetric model. In the original 3D model, the outer boundaries were all pressure far field.

Can anyone please tell how I must declare the boundaries.

Geometry: Half cone+cylinder arrangement

There is some initial clearance before the cone nose for simulating the flow from infinity.

Please let me know asap so that I can proceed with the work.

Can I upload any picture of my geometry. If so kindly let me know

Thanks.


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