How to get a convergence solution?

Conan · March 18, 2009, 01:40

In my case, I use Realizable k-e, and model is filled withTetrahedral grids (unstructure grid) but without any highly skewness.

The problem is, the continuity equation error does not drop down at 1.E-4, it is fluctuating around 5.E-3. The others are well.

Is there any methods to change the situation?

Thanks.

panda · March 18, 2009, 03:24

You may choose to see if other global variables under interest converge or not. Or, you may try to locally refine the mesh where the fluction is too apparent.

paka · March 20, 2009, 01:53

Try to increase number of internal iterations. If it is too low (this is relative), for example 20, after reaching 20 Fluent will assume this is the most accurate obtained solution and will proceed to the next iteration. Try to increase it to 40, but keep in mind the more iterations obviously the computational time will increase. Depending on your case I would say 60 is maximum, but again... depends what you are solving.

Krst

Conan · March 20, 2009, 03:06

where is the pannel for changing the internal iteration? I can not find. How to change?

paka · March 20, 2009, 03:28

In the top menu go to Solve, then Iterate.

I don't know how familiar you are with CFD. If you are not familiar with specifics of this panel, I would advise you to go to Fluent Documentation and read more about it: Try to find info about Iterate panel. This relates to theoretical basics of solution methods.

I hope this helps.

Conan · March 20, 2009, 04:35

My calulation is steady-state. NOT unsteady. So,there is no the corresponding setting pannel. In >Solve>Iterate, we can only set the total iteration number for outer cycle, rather than internal cycle.

March 18, 2009, 01:40	How to get a convergence solution?	#1
Conan New Member gnxie Join Date: Mar 2009 Location: Sweden Posts: 16 Rep Power: 17	In my case, I use Realizable k-e, and model is filled withTetrahedral grids (unstructure grid) but without any highly skewness. The problem is, the continuity equation error does not drop down at 1.E-4, it is fluctuating around 5.E-3. The others are well. Is there any methods to change the situation? Thanks.

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March 18, 2009, 03:24		#2
panda Member Join Date: Mar 2009 Posts: 35 Rep Power: 17	You may choose to see if other global variables under interest converge or not. Or, you may try to locally refine the mesh where the fluction is too apparent.

March 20, 2009, 01:53		#3
paka Senior Member Join Date: Mar 2009 Posts: 225 Rep Power: 18	Try to increase number of internal iterations. If it is too low (this is relative), for example 20, after reaching 20 Fluent will assume this is the most accurate obtained solution and will proceed to the next iteration. Try to increase it to 40, but keep in mind the more iterations obviously the computational time will increase. Depending on your case I would say 60 is maximum, but again... depends what you are solving. Krst

March 20, 2009, 03:06		#4
Conan New Member gnxie Join Date: Mar 2009 Location: Sweden Posts: 16 Rep Power: 17	where is the pannel for changing the internal iteration? I can not find. How to change?

March 20, 2009, 03:28		#5
paka Senior Member Join Date: Mar 2009 Posts: 225 Rep Power: 18	In the top menu go to Solve, then Iterate. I don't know how familiar you are with CFD. If you are not familiar with specifics of this panel, I would advise you to go to Fluent Documentation and read more about it: Try to find info about Iterate panel. This relates to theoretical basics of solution methods. I hope this helps.

March 20, 2009, 04:35		#6
Conan New Member gnxie Join Date: Mar 2009 Location: Sweden Posts: 16 Rep Power: 17	My calulation is steady-state. NOT unsteady. So,there is no the corresponding setting pannel. In >Solve>Iterate, we can only set the total iteration number for outer cycle, rather than internal cycle.