# turbulent viscosity limited to viscosity ratio...

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 August 29, 2003, 16:12 turbulent viscosity limited to viscosity ratio... #1 frank Guest   Posts: n/a 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

 August 29, 2003, 19:42 Re: turbulent viscosity limited to viscosity ratio #2 ap Guest   Posts: n/a 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 sanbhat, mm.abdollahzadeh, villager and 8 others like this.

 September 2, 2003, 20:59 Re: turbulent viscosity limited to viscosity ratio #3 frank Guest   Posts: n/a thanks i found the section where the turbulent viscosity ratio is high should i refine the grid there? frank

 September 2, 2003, 22:18 Re: turbulent viscosity limited to viscosity ratio #4 Lee Guest   Posts: n/a It happened to me in the beginning of iteration. As the solution get converging, it simply goes away.

 September 4, 2003, 07:13 Re: turbulent viscosity limited to viscosity ratio #5 ap Guest   Posts: n/a 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. Hi ap

 September 28, 2003, 17:31 Re: turbulent viscosity limited to viscosity ratio #6 johnnyb Guest   Posts: n/a It happened to me too, but went away after 22 iterations. 22 is very few, but is this something I should worry about?

 July 10, 2009, 10:33 #7 New Member   Join Date: Jun 2009 Posts: 4 Rep Power: 10 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

July 9, 2012, 02:54
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Quote:
 Originally Posted by Ama 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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July 9, 2012, 09:34
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Philipp
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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.

 July 9, 2012, 11:25 #10 Senior Member   Join Date: Mar 2011 Location: Germany Posts: 431 Rep Power: 13 any idea how to set turbulence boundary conditions?

 July 10, 2012, 04:08 #11 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 20 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.

 July 14, 2012, 01:01 #12 Senior Member   shoeb khan Join Date: Nov 2011 Posts: 179 Rep Power: 8 I want to know how to and when to use which turbulence models. Kindly give your comments. Regards shk

July 16, 2012, 03:09
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Philipp
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Quote:
 Originally Posted by shk12345 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.

 July 16, 2012, 03:51 #14 Senior Member   shoeb khan Join Date: Nov 2011 Posts: 179 Rep Power: 8 Suggest me name of some books Regards shk

July 16, 2012, 04:06
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Philipp
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Quote:
 Originally Posted by shk12345 Suggest me name of some books Regards 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?

 July 16, 2012, 04:11 #16 Senior Member   Marion Join Date: Jul 2012 Location: France Posts: 122 Rep Power: 8 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.

July 16, 2012, 04:14
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shoeb khan
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Quote:
 Originally Posted by Marion 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.

 March 31, 2013, 14:04 turbulent viscosity limited to viscosity ratio #18 New Member   Join Date: Mar 2013 Posts: 1 Rep Power: 0 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.

 April 10, 2015, 14:33 #19 Senior Member   Join Date: Mar 2013 Location: B'lr Posts: 127 Rep Power: 6 Can anyone explain me about free stream laminar and free stream turbulent viscosity?

 December 15, 2015, 23:54 #20 Senior Member   david Join Date: Oct 2012 Posts: 142 Rep Power: 7 Shivakumar, In the Navier-Stokes equation, you do not see a turbulent viscosity. It comes about when you do a Reynolds Average on the N.S equations. This is to account for the Reynolds stresses which is a product of the advection terms. The eddy viscosity is also used in the formulation of the gradient diffusion term to account for the triple correlations and pressure diffusion. NOTE: these are modelled terms and not explicit. So coming back to your question, to what is laminar and what is turbulent viscosity, the answer is this laminar viscosity is just the constant of the diffusion term in the N.S equation while turbulent viscosity is the "constant" used in RANS to model the reynolds stresses, etc. Hope this helps Stevie_1200 likes this.

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