CFD Online URL
[Sponsors]
Home > Forums > Main CFD Forum

filter width in LES

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 30, 2002, 13:02
Default filter width in LES
  #1
Kai
Guest
 
Posts: n/a
Dear all, I am doing some LES simulation on a circular cylinder with Reynolds Number of 10,000. this is run on CFX software with unstructured mesh. I get confused on how to create the mesh of the computational domain. should I create the mesh based on the Filter Width, or find out a filter width first and create the required mesh later.

all your help is appreciated.

Kai
  Reply With Quote

Old   October 2, 2002, 15:36
Default Re: filter width in LES
  #2
JONGDAE KIM
Guest
 
Posts: n/a
1. What kind of filter do you use?

2. If you use implicit filter (i.e. grid filter), the filter size is the length scale of grid.

3. In the case of implicit grid-filter, the grid size should be decided depends on the small scale flow structures.

4. Usually you can estimate the Kolmogorov length scale, and make mesh based on that scale. The smallest cells might have scales of 10-100 times larger than the Kolmogorov length scale.

5. If your numerical schemes are very stable and standard Smagorinsky model (only positive eddy viscosity), you may get reasonable (?) results even though your cell size is bigger than 100 times of Kolmogorov length scale.

6. Be careful close to the cylinder wall. What is the distance from the cylinder wall to the first grid point in your case? (In my case, square prism, 2% of D). 0.5% to 1% maybe enough in your case.

7. Not only the normal distance from the wall but also the spanwise length scales are also very importnat. If you want to investigate streamwise coherent structures, please read other literatures on the scale of the streamwise vortex (0.1D in square prism) and distances between the structures in spanwise direction (4D in square prism).

Kim.
  Reply With Quote

Old   October 3, 2002, 05:29
Default Re: filter width in LES
  #3
Kai
Guest
 
Posts: n/a
Thanks a lot for your guidance Kim,its helpful.

Catch you soon..

Kai
  Reply With Quote

Old   October 3, 2002, 07:04
Default Re: filter width in LES
  #4
Question.
Guest
 
Posts: n/a
How can one estimate the Kolmogorov scale (and hence the grid size) for a given flow.

Thank you.
  Reply With Quote

Old   October 3, 2002, 15:08
Default Re: filter width in LES
  #5
senthil
Guest
 
Posts: n/a
hi kim i have a question. how have u decided the distance of the first grid point from the wall of the square cylinder to be 2% of D? I mean on what basis i can calculate it. also how will you know the kolmogorov scales b4 calculations are made?

Thanx in advance. senthil
  Reply With Quote

Old   October 14, 2002, 09:38
Default Re: filter width in LES
  #6
CFD group
Guest
 
Posts: n/a
hi senthil, did u attend any turbulence course ?? if 'yes' then u should know how to calculate y+ and the first y grid point position before solving the prob. refer turbulence course lecture notes or any standard books.

CFD group

IITM
  Reply With Quote

Old   October 14, 2002, 10:56
Default Re: filter width in LES
  #7
senthil
Guest
 
Posts: n/a
who is this.Please have in mind that this is not the place to play...o.k... sorry if this hurt some ones feelings. senthil.k.b
  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
calculation of test filter quantites for desired parameters(equations) in les mrn FLUENT 0 July 15, 2010 06:04
LES with different filter Rick Main CFD Forum 1 August 22, 2008 19:10
Bugs in LES filter codes yekaniyasari OpenFOAM Bugs 3 February 18, 2008 02:59
question about les filter? Bin Li Main CFD Forum 2 January 21, 2004 13:04
LES filter xing zhang Main CFD Forum 3 November 15, 2003 14:50


All times are GMT -4. The time now is 17:25.