CFD Online Logo CFD Online URL
Home > Forums > FLUENT

viscosity ratio limited to 100000

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

LinkBack Thread Tools Display Modes
Old   July 7, 2008, 00:31
Default viscosity ratio limited to 100000
Woo Meng Wai
Posts: n/a
Sponsored Links

I am running a 3D simulation, k-e RNG, steady state, tetraheral grids, air medium with no rotating boundary.

In solving the model, I am taking a step-by-step

laminar -> std k-e -> RNG k-e

Managed to get convergence by monitoring the outlet velocity and temperature. However, upon convergence, if we let the model to continue iterating, once in a while the error message below will appear

turbulent viscosity limited to viscosity ratio of 1.000000e+005 in 1 cells

This happens once approximately every 200-250 iterations. A few questions on this:

1. Even with this occurrence, is my solution valid? 2. The error is only in 1 cell. What can be done to alleviate this? The solution mentioned is already using very fine grids at the region of high velocity gradient

Hope to further discuss this. Thank you.

Regards, Woo
  Reply With Quote
Sponsored Links

Old   July 7, 2008, 03:14
Default Re: viscosity ratio limited to 100000
ravi kumar
Posts: n/a

u should not get that kind of message anyway..

don t know why u have used laminar option for a turb. problem. no need to do like that. u can change over the options of k-e . if u r not getting that message for 100-200 iterations u can trat it as converged. the error msg comes b coz of improper b.c s for turbulence. o.k
  Reply With Quote

Old   July 7, 2008, 07:46
Default Re: viscosity ratio limited to 100000
Woo Meng Wai
Posts: n/a
Thanks RAvi,

Actually I do get that error message in the beginning. Like what you mentioned, it tapers off after a few hundred iterations. However, once the solution converges, the error message will appear once in a while, approximately every 250 - 300 hundred iterations.

As it is already converged and does not happend all the time, don't think it is because of inappropriate boundary conditions. Furthermore, it only occur in one cell. I am usinga total of 600,000 cells.

Any idea?

  Reply With Quote

Old   July 11, 2008, 12:59
Default Re: viscosity ratio limited to 100000
umesh javiya
Posts: n/a
See it is frequent problem with turbulence modelling with tetrahedral mesh and second order schemes for turb. dissipation rate ....

Ideally u should not get any messages ....

check where this cell is....may be u can improve mesh quality in this perticular area(like skewness, reduce mesh size, reduce mesh size jump etc......)

or u can use first order scheme for turb. dissipation rate equation and second order for rest equations.....

Most important thing...if ur solution looks physically right then ur solution is always right......and check/measure ur physically important quantity in domain....if they are right then ur sinulations are always right

  Reply With Quote


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 limited to viscosity ratio... frank FLUENT 19 December 15, 2015 23:54
turbulent viscosity limited to viscosity ratio Elizabeth FLUENT 13 December 16, 2014 09:57
Turbulent viscosity Limited to viscosity ratio Adrian FLUENT 12 September 21, 2011 04:22
turbulent viscosity limited to viscosity ratio mukkarum FLUENT 3 May 11, 2004 04:05
turbulent viscosity limited to viscosity ratio of Hua FLUENT 6 April 24, 2003 16:45

Sponsored Links

All times are GMT -4. The time now is 18:40.