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Old   August 29, 2003, 16:12
Default turbulent viscosity limited to viscosity ratio...
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frank
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of 1e5 in 140 cells?

i am not sure what this means but this was a message fluent gave me when i ran a simulation for drag using the k-e model. reynolds number is about 30 million. if you have ideas please let me know.

Frank
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Old   August 29, 2003, 19:42
Default Re: turbulent viscosity limited to viscosity ratio
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ap
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The turbulent viscosity ratio is defined as following:



turbulent viscosity
---------------------
laminar viscosity




FLUENT limits this ratio to a fixed value in order to obtain a stable solution.

Usually this limitation happens when you use a poor quality grid, or you specify wrong boundary conditions for turbulence variables.

Plot a contour of turbulent viscosity ratio. You'll identify where the problem happens. Try to refine the grid there. Also check turbulence boundary conditions.

Hi

ap
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Old   September 2, 2003, 20:59
Default Re: turbulent viscosity limited to viscosity ratio
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thanks i found the section where the turbulent viscosity ratio is high should i refine the grid there?

frank
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Old   September 2, 2003, 22:18
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It happened to me in the beginning of iteration. As the solution get converging, it simply goes away.
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Old   September 4, 2003, 07:13
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ap
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Yes. Try to refine the grid.

Also, if you use first order discretization scheme, try to switch to a higher order one.

As Lee said, it's possible that you'll have this warning message during the first iterations. If it will disappear, don't consider it as a problem.

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ap
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Old   September 28, 2003, 17:31
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It happened to me too, but went away after 22 iterations. 22 is very few, but is this something I should worry about?
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Old   July 10, 2009, 10:33
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hi,

do you know how to refine the grids where tubulant viscosity is limited ??

when i run my program it does give me as : "viscosity ratio is limited to viscosity ratio of 100000000 in ........... cells" and also "reversed flow in ... face on outflow ...."

how can i resolve this?

Please i need your help.

Many thanks !!

Ama
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Old   July 9, 2012, 02:54
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Quote:
Originally Posted by Ama View Post
hi,

do you know how to refine the grids where tubulant viscosity is limited ??

when i run my program it does give me as : "viscosity ratio is limited to viscosity ratio of 100000000 in ........... cells" and also "reversed flow in ... face on outflow ...."

how can i resolve this?

Please i need your help.

Many thanks !!

Ama
It is better to correct your mesh in gambit, else you can refine it in fluent, refine the places which turbulence is higher than a value.
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Old   July 9, 2012, 09:34
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Quote:
Originally Posted by johnnyb
;108196
It happened to me too, but went away after 22 iterations. 22 is very few, but is this something I should worry about?
No, don't worry. If it vanishes during calculation, it is just due to a bad initial guess. This is not a problem for your final results.
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Old   July 9, 2012, 11:25
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any idea how to set turbulence boundary conditions?
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Old   July 10, 2012, 04:08
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Once you chose a turbulence model, new checkboxes and input fields become available in the boundary conditions of your inlets and outlets. Here You can set the turbulence boundary conditions as well.
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Old   July 14, 2012, 01:01
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I want to know how to and when to use which turbulence models.
Kindly give your comments.
Regards
shk
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Old   July 16, 2012, 03:09
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Quote:
Originally Posted by shk12345 View Post
I want to know how to and when to use which turbulence models.
Kindly give your comments.
Regards
shk
Your question is much too open to be answered in a forum. I don't think anybody will have the patience to give you an adequate answer. I strongly recommend to read several books about that.
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Old   July 16, 2012, 03:51
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Suggest me name of some books

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shk
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Old   July 16, 2012, 04:06
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Quote:
Originally Posted by shk12345 View Post
Suggest me name of some books

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shk
All books I have only have small chapters about exactly that topic. But this one is really one of the best CFD books:
"An Introduction to Computational Fluid Dynamics - The Finite Volume Method", H K Versteeg, W Malalasekera
with some pros and cons about important models. (But again, just a small chapter)

I got several other superb books, unfortunately for You: They are on German...

Also this paper:
"Hybrid LES/RANS methods for the simulation of turbulent flows", Jochen Fr๖hlich, Dominic von Terzi
is brilliant - if You are interested in unsteady turbulence modelling.

What kind of flow are You interested in?
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Old   July 16, 2012, 04:11
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Hi,
On CFD online you have a section called "books" and a subsection "turbulence" http://www.cfd-online.com/Books/brow...?category_id=4
That's where I found the reference to "Turbulence modeling for CFD" - I find it very interesting, even though I havent finished it yet :-)
Marion.
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Old   July 16, 2012, 04:14
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Quote:
Originally Posted by Marion View Post
Hi,
On CFD online you have a section called "books" and a subsection "turbulence" http://www.cfd-online.com/Books/brow...?category_id=4
That's where I found the reference to "Turbulence modeling for CFD" - I find it very interesting, even though I havent finished it yet :-)
Marion.
Thanks for the reference.
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Old   March 31, 2013, 14:04
Default turbulent viscosity limited to viscosity ratio
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Hello, my friends!
I model ispernie water droplets in contact with the flow of highthermal (steam). After several iterations of the message ' turbulent viscosity limited to viscosity ratio ' Solver takes off. The reason?
Eulerian model and turbulence to the k-omega.
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Old   April 10, 2015, 14:33
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Can anyone explain me about free stream laminar and free stream turbulent viscosity?
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