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

Turbulent viscosity ratio

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 28, 2003, 12:40
Default Turbulent viscosity ratio
  #1
Jurgen
Guest
 
Posts: n/a
I am using the standard k-e turbulence model in a quite large grid, about 1 mio. cells. I cannot improve the number on grid cells anymore. During iteration, I get the message that the turbulent viscosity is limited to a viscosity ratio of 1E+5. I know how to change this limit, this is not the point, more how to deal with this problem. Besides, the solution is converging very (!) slowly. Any ideas someone?

Regards, Jrgen
  Reply With Quote

Old   January 28, 2003, 15:56
Default Re: Turbulent viscosity ratio
  #2
Erwin
Guest
 
Posts: n/a
Some thoughts:

1) I don't know what a realistic limit for the ratio is. In the past there was some discussion whether such high turbulent viscosities were realistic or not. People disagreed. I guess it depends on what kind of flow problem you have, two-phase or single-phase, material properties etc. What i am trying to say: sometimes a ratio of 1e5 might be realistic ...

2) If you are sure it is not realistic you could try to fool the solver and set the limit to a lower value that is in the right ballpark, something like 5000 or so. That could force better convergence behavior.

3) Also, this message could indicate a mesh problem. Either something simple, like you forgot to scale the grid. Or something more problematic like cell skewness too high.

4) Last but not least: initialize with good values, also for k and epsilon. This can make a huge difference. If the flow field has been initialized poorly it can take ages for the solver to get out of it (as you may be experiencing). Reinitializing can save a lot of time.
  Reply With Quote

Old   January 29, 2003, 03:23
Default Re: Turbulent viscosity ratio
  #3
Jurgen
Guest
 
Posts: n/a
Right, skewness, I have a few cells with skewness arounf 0.8. Couldn't get rid of tose without increasing the grid size even further. Thanks for the input, Jrgen
  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
Turbulent viscosity ratio Balaji FLUENT 5 May 27, 2014 03:47
hel (turbulent viscosity ratio limited) for supersonic combustion problem omar.2002bh FLUENT 2 September 5, 2012 11:04
setting value of turbulent intensity and turbulent viscosity ratio in wind tunnel nuimlabib Main CFD Forum 0 August 4, 2009 00:05
On limiting to turbulent viscosity ratio! varghese FLUENT 2 November 15, 2003 09:56
Problem of Turbulent Viscosity Ratio Limited David Yang FLUENT 3 June 3, 2002 06:13


All times are GMT -4. The time now is 23:22.