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

y+ calculations

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 24, 2002, 09:14
Default y+ calculations
  #1
henry
Guest
 
Posts: n/a
hi

Does any one now how to calculate the distance a near wall cell should be ,if I know the flow details, and I want to maintain the y+ between 30 and 100 as per CFX.

please help.

henry
  Reply With Quote

Old   May 24, 2002, 09:41
Default Re: y+ calculations
  #2
cfd guy
Guest
 
Posts: n/a
Hi,
In TASCflow and CFX-5 the yplus values at walls are stored by default in the results file. In CFX-4 you only need to add three lines in your command file to see these values under the post-processor.
Regards, cfd guy
  Reply With Quote

Old   May 24, 2002, 11:36
Default Re: y+ calculations
  #3
Robin
Guest
 
Posts: n/a
Actually, TASCflow will only output yplus values if the BCINFO = t flag is set.

As an initial guess before you run for the first time, there are correlations for boundary layer development over a flat plate. Look up section 4.4.4 of the TASCflow doc for details, or Mathmatical Models and Solution Algorithms > Modelling Flow Near the Wall > Guidelines for Grid Generation section of the CFX-5.5 doc (see math_models.pdf).

Regards, Robin
  Reply With Quote

Old   May 27, 2002, 09:45
Default Re: y+ calculations
  #4
Michael Bo
Guest
 
Posts: n/a
http://geolab.larc.nasa.gov/APPS/YPlus/
  Reply With Quote

Old   May 27, 2002, 09:47
Default Re: y+ calculations
  #5
henry
Guest
 
Posts: n/a
hi Thanks for the info,

but I wanted the formula to calculate the Y+

from the flow variables like Re ,etc

henry
  Reply With Quote

Old   May 27, 2002, 10:01
Default Re: y+ calculations
  #6
henry
Guest
 
Posts: n/a
hi

Could some one give the formula please.

joe
  Reply With Quote

Old   May 28, 2002, 09:41
Default Re: y+ calculations
  #7
Patrice Jaumouillie
Guest
 
Posts: n/a
y+, the dimensionless distance from the wall, can be calculated from the formula :

y+=(rho.u*.y)/mu

where rho and mu are respectively the density and the dinamic viscosity of the fluid, y is the distance from the wall and u* is the shear velocity.

The three regions are (may vary from different authors) :

The viscous sublayer 0<y+<5 The intermediate zone : 5<y+<30 The turbulent zone : 30<y+<500

Regards.
  Reply With Quote

Old   May 30, 2002, 17:43
Default Re: y+ calculations
  #8
Robin
Guest
 
Posts: n/a
Have a look at the documentation, it's in there.

Robin
  Reply With Quote

Old   June 3, 2002, 04:38
Default Re: y+ calculations
  #9
henry
Guest
 
Posts: n/a
hi

Patrice thanks soo much ,

do you know how the shear velocity is calculated.

thanks again

joseph
  Reply With Quote

Old   June 27, 2002, 21:48
Default Re: y+ calculations
  #10
Min-Hua Wang
Guest
 
Posts: n/a
Hello, All:

I am very interested in this topic. I am using CFD-4 now. I am trying to export y+ data from the simulation.

It seems to me that one can obtain some meanfull y+ values as the wall is still (not moving). Do I still expect the correct y+ values from the simulation with a standard wall function if the wall is in moving ( bassically the wall is rotating in my study)?

Min-Hua Wang
  Reply With Quote

Reply


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
Hardware for Cfx/openfoam calculations of 30-50 million cells Rkeck Hardware 8 July 13, 2009 13:12
transient calculations! lelia Siemens 9 April 14, 2008 09:33
Mass Flux values and calculations Cb Siemens 1 January 22, 2005 10:21
Difference between two calculations Lennart FLUENT 7 November 24, 2002 02:19
Implicit transient calculations using Fluent5 G. Berntsen Main CFD Forum 4 November 10, 1999 16:32


All times are GMT -4. The time now is 17:44.