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

Airfoil y+ Results Query

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 22, 2007, 03:18
Default Airfoil y+ Results Query
  #1
asd
Guest
 
Posts: n/a
I am validating an airfoil at Re=6 million at mach 0.32 within FLUENT. I have found over the five grids examined thus far that a grid with approx. 92,000 cells at y+ about 150-300 produces lift and drag results that are within 3-4% of experimental data, over an AOA range of -1 to 12 deg.

Since i am using the SST k-w model, i would like to further test result convergene by increasing the number of cells such that y+ of 1 can be obtained. I am limited in my computer resources so have been able to achieve a y+ of 25, yet my results are now worst off, than they were with a y+ of 150-300. I have maintained a cell grid aspect ratio of ~20 within the BL, and have about 340 grid points on the airfoil surface. I am confused as to why my results are worst off now; i would have expected similar results or slight improvement given that the y+ has been reduced to capture the visoucs sub-layer. Would they deteoriate even further if i was to achive a y+ of 1? Any advice???

  Reply With Quote

Old   June 22, 2007, 08:02
Default Re: Airfoil y+ Results Query
  #2
Mani
Guest
 
Posts: n/a
The fact that you're getting reasonable drag results with a very high y+ of around 200 implies that the turbulence model is using wall functions. Depending on the approach, the model may actually require a reltively high y+ in order to work (e.g. some wall functions methods require that the first grid point off the wall is within the log region of the boundary layer). Furthermore, depending on the method, not only the first grid cell is important, but also how many cells fall within the boundary layer. You better read the manual and find out what method Fluent is using, what options you have, and what the requirements are on grid resolution and y+.
  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
[GAMBIT] Meshing airfoil using .dat file problem creggie ANSYS Meshing & Geometry 10 June 27, 2010 19:24
FloWorks Airfoil Info trvo FloEFD, FloWorks & FloTHERM 2 March 4, 2010 09:02
[FloWorks] Request advice for an airfoil calculation problem Bogey Jammer Main CFD Forum 0 September 29, 2009 17:06
ICEM CFD Airfoil Tutorial Input Tom ANSYS Meshing & Geometry 1 September 25, 2009 06:50
Airfoil y+ for Validation Purposes asd FLUENT 3 June 26, 2007 09:27


All times are GMT -4. The time now is 22:07.