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warning turbulent viscosity ratio limiltation

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Old   March 8, 2009, 12:09
Default warning turbulent viscosity ratio limiltation
  #1
Shamoon
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Hi all

i am running a case of ONERA M6 wing with k omega sst. my mesh is about 0.3 M cells. I get warnings of turbulent viscosity ratio limitatioon after 1000 iterations, warning is in 100 cells. ca anybody tell me whats the cause of this warning and how it can be rectified?

regards
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Old   March 8, 2009, 14:47
Default Re: warning turbulent viscosity ratio limiltation
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Freeman
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I guess that your Re is quite high: this problem can be solved by refining your mesh where flow has high gradients of pressure, velocity/vorticity gradients...

Try to visualize these cells with high viscosity ratio an refine your mesh in this area.

Regards

Freeman
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Old   March 8, 2009, 18:10
Default Re: warning turbulent viscosity ratio limiltation
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Shamoon
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i cant visualize them because they are not on the walls or symmetry or pressure far field etc they are iside the interior and its difficult to visualize there
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Old   March 9, 2009, 02:45
Default Re: warning turbulent viscosity ratio limiltation
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Freeman
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No problem with that: to visualize internal cells, just do the following:

1. "Adapt"->"gradients" make your choices and then "Mark" this cells for adaption (do not click "Adapt" yet). 2. Go to "Adapt"->"Manage", make shure your actual register in "registers" is the one you want to visualize, click "Options", and let be enhabled "Wireframe" in both "refine" and "coarsen". You can also display your boundary "Grid" faces, with "Filled" rendering. Then click "OK" 3. Click "display" and you will visualize your marked cells ready for the refinement (or coarsening, if any). 4. CLick "Adapt" to finally apply the defined refinement.

Hope this was clear. Regards,

Freeman
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Old   March 9, 2009, 07:39
Default Re: warning turbulent viscosity ratio limiltation
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Shamoon
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Do I have to reinitialize the solution when I adapt my grid?
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Old   March 9, 2009, 07:49
Default Re: warning turbulent viscosity ratio limiltation
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Freeman
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No! Just continue the iterations from you stopped...
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Old   March 10, 2009, 12:52
Default Re: warning turbulent viscosity ratio limiltation
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Shamoon
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I did the following:

I selected "Gradients of.."---> "Turbulent viscosity Ratio" and check only the refine option (is it OK?) next it was showing that the refine threshold is 1e+5 I click on Mark and then it said 0 out of 0 cells marked for refinement 0 out out zero cells for coarsening

N.B The warning was turbulent viscosity limited to 1e+5 in 73 cells

Regardds

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Old   March 10, 2009, 14:27
Default Re: warning turbulent viscosity ratio limiltation
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Freeman
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Of course, if your threshold is 1e5 and fluent limits by default turbulence viscosity ratio (TVR) in 1e5 that means... that no cell will be marked for refinement! Just change the threshold to a value for example 50.000 or similar below 1e5.

By the way, how many cells has your domain? 73 cells seems to be quite low if they represent only let's say 3% of your domain. Also if your flow regime is high and you have very strong recirculations is not rare to have a high TVR warning.

Regards,

Freeman
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Old   March 10, 2009, 17:58
Default Re: warning turbulent viscosity ratio limiltation
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Shamoon
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I have the case of transininc flow (possibility of lambda shock) M=0.88 on ONERA M6 wing and no of cells are 0.3 million approx.
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Old   March 11, 2009, 05:48
Default Re: warning turbulent viscosity ratio limiltation
  #10
Freeman
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OK, 76 over 300.000 cells is about 0.025% of your domain, this is not critical, as far as these cells are not close to your wing (I guess they are in the wake of the wing): I would not get really mad about it... Are you using coupled solver for that M=0.8? Which turbulence model? Coulped solver is far much complex as segregated to converge and may lead to this high TVR if combined with RSM, Realizable or k-w turbulence models.

Hope that anyelse throw an opinion to your TVR, but I find it pretty correct.

Regards,

Freeman
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Old   March 11, 2009, 06:05
Default Re: warning turbulent viscosity ratio limiltation
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Shamoon
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Yes the solver is coupled (density based) and the model is k omwga standard
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