CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Massage of turbulent viscosity limited to viscosity ratio

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree2Likes
  • 1 Post By CeesH
  • 1 Post By shereez234

Reply
 
LinkBack Thread Tools Display Modes
Old   December 21, 2015, 15:59
Default Massage of turbulent viscosity limited to viscosity ratio
  #1
Senior Member
 
Aja
Join Date: Nov 2013
Location: Germany
Posts: 372
Rep Power: 6
aja1345 is on a distinguished road
Hi,

When i am running my simulation, the following message is appeared. Why?

"turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 18987 cells 33 3.7137e-02 1.5782e-02 6.7494e-02 8.9973e-03 1.8689e-02 4.5216e-02 -2.9683e+01 1874:07:22 4999967"

Is there any problem?

I change maximum turb viscosity ratio to high values in Solve>control>limit and this above massage doesn't appear. Am I right?

Best.

Thanks.
aja1345 is offline   Reply With Quote

Old   December 21, 2015, 16:09
Default
  #2
Senior Member
 
Cees Haringa
Join Date: May 2013
Location: Delft
Posts: 440
Rep Power: 9
CeesH is on a distinguished road
It may or may not be a problem, but the limiter is there for a reason. In by far the majority of simulations, such high turbulent viscosities will not be realistic (maybe you could encounter them in high-density fusion plasmas or so, but they are not present in anything I've encountered). So although changing the limiter removes the message, the question is still, are your turbulence values realistic?

In many cases where I encountered the warning, the simulation was soon to diverge - in some cases the warning went away with time though and was in that respect an artifact of the solution process. So what you can try is give it some time, if the warning disappears with time, it's fine. If not, you will need to find the underlying reason. Which probably means you need some mesh refinement, maybe a smaller timestep, etc.

Good luck!
aja1345 likes this.
CeesH is offline   Reply With Quote

Old   December 21, 2015, 17:46
Default
  #3
Senior Member
 
shereez234's Avatar
 
shereez
Join Date: Jan 2014
Location: England
Posts: 202
Rep Power: 5
shereez234 is on a distinguished road
Ceesh is right. It indicates a non physical solution in existence. However, I would like to add something to that.

From my experience, since you are the one who is managing the solution and it's limits, you may be able to increase and decrease the limits of any parameter to a limit that you would like. Therefore, this will eliminate the error message and thus make you happy. However, this is violating one of the major concepts of cfd which is boundedness of the solution.

A lot of the times, people use the wrong Turbulent viscosity ratios and wrong Turbulent Intensities( too high or too low) to initialize the solution and therefore the resulting simulation is not physical.

For instance, if you are repeating a wind tunnel experiment, the best practice would be to find out, estimate or research about typical Turbulent Viscosity ratios at the inlet, and Turbulent intensities input too( or Length scale etc..) . This will lead to a better solution and can make the solution lie in the physical limits which makes more sense.

Hope this was helpful.

Regards

Shereez
aja1345 likes this.
shereez234 is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Problem with divergence TDK FLUENT 11 July 31, 2016 06:03
RSM+2nd ordedr causes turbulent viscosity limited to viscosity ratio of.... khsiavash Main CFD Forum 10 January 7, 2016 13:30
"turbulent viscosity limited to viscosity ratio" olivier FLUENT 11 October 10, 2015 05:49
turbulent viscosity ratio bmikuz OpenFOAM Paraview & paraFoam 2 July 4, 2014 02:59
On limiting to turbulent viscosity ratio! varghese FLUENT 2 November 15, 2003 09:56


All times are GMT -4. The time now is 16:26.