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May 10, 2011, 07:52 
simpleFoam crash > How to solve

#1 
Senior Member
Join Date: Mar 2011
Posts: 155
Rep Power: 6 
Hi there,
I have tried to solve a case with simpleFoam. Turbulence model: kepsilon, thus y+>30. In the picture you can see yplus values of about >6000. I'm not quite sure if the value of yplus is limitted for kepsilon. I have only read greater than 30. I would now suggest, to finer the mesh on the area of high values of yplus. I have also uploaded another picture of pyFoamPlotWatcher. I still have tried to manipulate the value pf alpha (relaxation factors). I'm afraid I tried with no success. Does someone have an idea how to manipulate with success? epsilon_max gets also a very strange values. I'm happy for every answer. Best Regards, tH3f0rC3 

May 11, 2011, 02:44 

#2 
Senior Member
Join Date: Mar 2011
Posts: 155
Rep Power: 6 
The new case I have tried to solve, the one with a finer mesh (yPlus max = 290) crashes also, but in a different way:
Please see the added picture When I try to modify the alpha values (relaxation factors) I don't get better results. Maybe someone of you has a better idea. Best Regards, tH3f0rC3 

May 11, 2011, 13:11 

#3 
Member
Freeman Adane
Join Date: Apr 2010
Posts: 42
Rep Power: 7 
it doesn't look like the crash is coming from "yplus" or the ke model itself, rather it might be you're driving the flow "too fast". Try ff:
1. Consider, reducing the relaxation factors, especially the momentum terms. 2. If it persists, then try first with UDS (first order scheme) if you're not using it and then later change it to higher order to scheme. 3. try to review where which region has this abnormal feature and maybe, consider refining your mesh or something in that line.... 4. if the above fails, then switch to different solver which allows the transient term. When using this method, change the starttime to be "0" and NOT "latesttime" since you're solving pseudotransient problem. This method will allow you to use small timestep to drive the flow "slowly". best wishes! 

May 11, 2011, 14:56 

#4  
Senior Member
Join Date: Mar 2011
Posts: 155
Rep Power: 6 
Hi,
thanks for your answer. Please see my notations below. Best Regards, tH3f0rC3 Quote:
Last edited by tH3f0rC3; May 12, 2011 at 02:56. 

May 12, 2011, 07:07 

#5 
Senior Member
Join Date: Mar 2011
Posts: 155
Rep Power: 6 
I think I have now solved the problem.
I have used as boundary condition for inlet U: type fixed Value Now I am using type surfaceNormalFixedValue and it works so far. Best Regards, tH3f0rC3 

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