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RSM+2nd ordedr causes turbulent viscosity limited to viscosity ratio of....

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Old   July 29, 2009, 12:44
Default RSM+2nd ordedr causes turbulent viscosity limited to viscosity ratio of....
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khsiavash
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Dear friends
I have modeled "opposed coollant jets injected normally into a heated confined crossflow".
Problem statement: -fluid: incomp ideal gas - Ujets=75m/s -U(crossflow)=13.7m/s
-Symmetry planes are considered – D(jets)=8mm Inlet Area=0.02*0.1m2 Total length of Crossflow=0.7m
Also I`ve checked the inlet values and also Ypluse (for proper WF), in addition I`ve maked 640000 hexahedral mesh in reasonable way.

My Problem: when I have used RSM model + second order upwind order of descretization, I have received this error: " turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2 cells--continue to 20000 cell or more up to "floating point!!!
Notice:But in other turbulence models(ske-rke-RNG ke-v2f) even with second order, I reached to reasonable answers.I`ve started with ske then I`ve switched on RSM or I`ve started with 1st order then I`ve switched on 2nd order (in RSM).In addition I`ve reduced the URF of Reynolds Stresse.nothing happened, again I faced with that error.
What is wrong with RSM+2nd order?
Do you have any suggestion?
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Old   April 4, 2011, 08:04
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I have read through many posts, this one describes my problem very good. I have exactly the same problem with 2nd order RSM.

Increasing Turb Visc ratio to 1e20 => floating point error
All URF => 0.1 => still the same problem.

I have already read through fluent manual, CFD Wiki und over 50 threads on the forum.
Thank you very much!
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Last edited by pz1337; April 4, 2011 at 12:17.
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Old   April 4, 2011, 14:34
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Oh well, this should be in ANSYS/FLUENT ... if a moderator/admin would be so kind, thank you very much!
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Old   October 19, 2011, 03:10
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Hello,

I am in a similar situation, did you ever solve the case?.

Thank you.

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Old   October 19, 2011, 03:14
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I did not and used k-e Realizable in the end....
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Old   October 19, 2011, 03:37
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Ok, thanks. The only way I found to solve the problem by adapting the mesh based on the isovalue of turbulent viscosity ratio. The drawback is that after adaptation resulting number of cells is very high, multiplying the original number of cells per 5.
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Old   October 19, 2011, 05:38
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whats the ASPECT RATIO of mesh? Because I have similar problems and I have concluded that it is due to the aspect ratio. Typically aspect ratio should be atleat 100 and better is even less. With aspect ratio 100 one should also switch to the double precision solver
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Old   October 19, 2011, 06:21
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Hi Far,

Double precision mode was activated. The aspect ratio is 57 and skewness 0.51. I think they are acceptable values but perhaps not good enough for an enhanced wall treatment.

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