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-   -   turbulent viscosity limited to viscosity ratio... (http://www.cfd-online.com/Forums/fluent/32055-turbulent-viscosity-limited-viscosity-ratio.html)

 frank August 29, 2003 16:12

turbulent viscosity limited to viscosity ratio...

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

 ap August 29, 2003 19:42

Re: turbulent viscosity limited to viscosity ratio

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

 frank September 2, 2003 20:59

Re: turbulent viscosity limited to viscosity ratio

thanks i found the section where the turbulent viscosity ratio is high should i refine the grid there?

frank

 Lee September 2, 2003 22:18

Re: turbulent viscosity limited to viscosity ratio

It happened to me in the beginning of iteration. As the solution get converging, it simply goes away.

 ap September 4, 2003 07:13

Re: turbulent viscosity limited to viscosity ratio

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

 johnnyb September 28, 2003 17:31

Re: turbulent viscosity limited to viscosity ratio

It happened to me too, but went away after 22 iterations. 22 is very few, but is this something I should worry about?

 Ama July 10, 2009 10:33

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?

Many thanks !!

Ama

Quote:
 Originally Posted by Ama (Post 222277) 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.

 RodriguezFatz July 9, 2012 09:34

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.

 cfd seeker July 9, 2012 11:25

any idea how to set turbulence boundary conditions?

 RodriguezFatz July 10, 2012 04:08

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.

 shk12345 July 14, 2012 01:01

I want to know how to and when to use which turbulence models.
Regards
shk

 RodriguezFatz July 16, 2012 03:09

Quote:
 Originally Posted by shk12345 (Post 371388) 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.

 shk12345 July 16, 2012 03:51

Suggest me name of some books

Regards
shk

 RodriguezFatz July 16, 2012 04:06

Quote:
 Originally Posted by shk12345 (Post 371565) 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 Fröhlich, Dominic von Terzi
is brilliant - if You are interested in unsteady turbulence modelling.

What kind of flow are You interested in?

 Marion July 16, 2012 04:11

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.

 shk12345 July 16, 2012 04:14

Quote:
 Originally Posted by Marion (Post 371569) 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.

 D_SH March 31, 2013 14:04

turbulent viscosity limited to viscosity ratio

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.

 shivakumar April 10, 2015 14:33

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

 davidwilcox December 15, 2015 23:54

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 :)

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