# divergence detected in AMG solver ?

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 February 24, 2010, 12:54 divergence detected in AMG solver ? #1 New Member   Join Date: Feb 2010 Posts: 7 Rep Power: 9 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

 March 23, 2010, 07:00 divergence detected in AMG solver: pressure correction #2 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 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.

 March 25, 2010, 19:47 #3 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 10 Hi are u using steady or unsteady solver ?

 March 25, 2010, 21:05 divergence amg solver #4 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 unsteady solver; spalart almaras model; five stage runge kutta time stepping scheme

 March 26, 2010, 02:51 #5 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 10 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.

 March 26, 2010, 14:20 autosave command #6 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 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.

 March 26, 2010, 18:45 #7 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 10 Hi again File--->write--->autosave then u can choose saving frequency Regards

 March 26, 2010, 19:08 #8 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 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.

 March 27, 2010, 07:07 #9 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 10 yes if u dont change simulation parameters, u just need to save data files (without case files)

 March 27, 2010, 07:14 #10 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 Thanks. I got you.

 March 29, 2010, 15:57 #11 New Member   Srikrishna Join Date: Mar 2010 Posts: 13 Rep Power: 9 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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