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August 29, 2003, 16:12 
turbulent viscosity limited to viscosity ratio...

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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 ke 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

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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 

September 2, 2003, 20:59 
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 

September 2, 2003, 22:18 
Re: turbulent viscosity limited to viscosity ratio

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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

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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. Hi ap 

September 28, 2003, 17:31 
Re: turbulent viscosity limited to viscosity ratio

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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?


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 

July 9, 2012, 02:54 

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Quote:
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Saeed Sadeghi Ansys Fluent CFD Consultant 

July 9, 2012, 09:34 

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Philipp
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Quote:


July 9, 2012, 11:25 

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any idea how to set turbulence boundary conditions?


July 10, 2012, 04:08 

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Philipp
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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.


July 14, 2012, 01:01 

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shoeb khan
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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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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 

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shoeb khan
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Suggest me name of some books
Regards shk 

July 16, 2012, 04:06 

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Philipp
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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 

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Marion
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Hi,
On CFD online you have a section called "books" and a subsection "turbulence" http://www.cfdonline.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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March 31, 2013, 14:04 
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 komega. 

April 10, 2015, 14:33 

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Can anyone explain me about free stream laminar and free stream turbulent viscosity?


December 15, 2015, 23:54 

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Shivakumar,
In the NavierStokes 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 

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