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

grid independence

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 2, 2003, 07:16
Default grid independence
  #1
chanchala
Guest
 
Posts: n/a
Hi,

If you found the grid independent solution for a certain geometry using say, standard wall functions and k-epsilon turbulence model, would this mesh still be grid independent if you change to Re-stress model or non-equilibrium wall functions? Or would you have to carry out a grid indepence test again?

thanks, Chanchi
  Reply With Quote

Old   December 2, 2003, 07:21
Default Re: grid independence
  #2
chanchala
Guest
 
Posts: n/a
Another question,

With non-equilibrium wall functions is there a recommended y+ value for the cells at the wall?
  Reply With Quote

Old   December 2, 2003, 16:32
Default Re: grid independence
  #3
ap
Guest
 
Posts: n/a
The y+ range is the same of standard wall-functions (y+ between 30 and 60).

For the enhanced wall treatment, you should have y+ close to 1 and, anyway, lower than 4.

Hi

ap
  Reply With Quote

Old   December 3, 2003, 13:20
Default Re: grid independence
  #4
AMV
Guest
 
Posts: n/a
Why are you so much bothered about grid independence. In whatever model you are using, you will definitely find that if your entire range of y+ is less than say 500 for a grid and less than 100 for another grid, the results like velocity profile at outlet etc would match considerably. Thus the only thing you should make sure is that your y+ is < 500. Also, unless its your research topic, dont go too much details of near wall flows, as nobody knows which approach is better. If you are asking engineering solutions, then k-epsilon with std wall functions is best approach.
  Reply With Quote

Old   December 8, 2003, 12:11
Default Re: grid independence
  #5
chanchala
Guest
 
Posts: n/a
Hi AMV (and ap),

Thanks for your comments. I'm doing a PhD and my pipe geometry is very curved so I thought it might be interesting to check what the effect of the different near wall models may be since the flow is governed by the curvature of the walls. It's only as a point of interest rather than a problem actually.

thanks, chanchi
  Reply With Quote

Old   December 9, 2003, 12:20
Default Re: grid independence
  #6
AM Vaidya
Guest
 
Posts: n/a
If this is the case, then you should be really careful and should do proper exercise. Have you read following ? 1) Chen H.C., Patel V.C., Near wall turbulence models for complex flows including separation, AIAA, 26, No.6, June 1988. 2)Amano R.S., Development of a turbulence near-wall model and its application to separated and reattached flows, Numerical Heat Transfer, 7, 59 - 75, 1984. 3)Chieng C.C. and Launder B.E., On the calculation of turbulent heat transport downstream from an abrupt pipe expansion, Numerical Heat Transfer, 3, 189 -207, 1980. 6)Launder B.E. and Spalding D.B., The numerical computation of turbulent flows, Computational Methods in Applied Mechanics and Engineering, 3, 269-289, 1974.
  Reply With Quote

Old   December 9, 2003, 12:22
Default Re: grid independence
  #7
AM Vaidya
Guest
 
Posts: n/a
I forgot to give your answer in previous answer.

You will have to carry out grid independence test for each model separately.
  Reply With Quote

Old   December 9, 2003, 12:58
Default Re: grid independence
  #8
chanchala
Guest
 
Posts: n/a
Hi Thanks so much for those references. I have reserved a few books from the library on the subject but they seem to always be out! I'll get these immediately.

chanchi
  Reply With Quote

Old   December 9, 2003, 13:04
Default Re: grid independence
  #9
AM Vaidya
Guest
 
Posts: n/a
great . you r welcome for any future discussion .
  Reply With Quote

Old   January 11, 2004, 00:07
Default Re: grid independence
  #10
s
Guest
 
Posts: n/a
i think it is not neccesary, then we must carry out mesh study for every boudnary condition.
  Reply With Quote

Old   January 11, 2004, 06:45
Default Re: grid independence
  #11
AMV
Guest
 
Posts: n/a
strictly speaking yes
  Reply With Quote

Old   January 11, 2004, 07:50
Default Re: grid independence
  #12
simple
Guest
 
Posts: n/a
how can u say that . do u have any reference
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
grid independence questions lucifer FLUENT 0 December 14, 2009 20:59
unstructured mesh grid independence for Fluent Shane Schouten FLUENT 0 October 11, 2006 17:50
Grid independence check Mattis Voss FLUENT 1 November 23, 2005 11:30
Grid Independence problem for simple pipe geometry chanchala FLUENT 13 November 20, 2003 09:24
Combustion Convergence problems Art Stretton Phoenics 5 April 2, 2002 06:59


All times are GMT -4. The time now is 15:11.