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

Wall coordinates and boundary layer thickness

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 1, 2011, 18:18
Default Wall coordinates and boundary layer thickness
  #1
New Member
 
Ben
Join Date: Dec 2010
Location: Ontario, Canada
Posts: 1
Rep Power: 0
bentmol is on a distinguished road
Is there a simple scaling between wall coordinates and the boundary layer thickness?

The only book that I have read that even attempts to relate wall coordinate y+ with the boundary layer thickness [BLT] is "Applied Fluid Dynamics Handbook" by Blevins. He suggests that 0.005 x BLT = y+ = 10, 0.1 x BLT = y+ = 300 and BLT = y+ = 3000, pertaining only to turbulent flow over flat plate.

Blevins says that these relationships are highly approximate. After plugging in the formulas involving friction factor, wall coordinates and BLT, I find that the relationship between wall coordinates and boundary layer coordinates depends on the local Reynolds number Re = Ux/[kinematic viscosity]. I get

y/BLT = 60.9 x [y+] times Re^-0.7857

based on the friction factor formulas that I found in Blevins' book, for flow over a flat plate. Other formulas in other books will result in a somewhat different Reynolds number dependence and the numerical constants will vary too.

But, there seems to be no simple conversion between the 2 coordinate systems.

Is this the right conclusion?

Ben
bentmol is offline   Reply With Quote

Old   July 3, 2011, 21:44
Default
  #2
Member
 
Join Date: Feb 2010
Location: Australia
Posts: 65
Rep Power: 16
RossFS is on a distinguished road
I'd say that your conclusion is correct as you can set the y+ value arbitrarily as it's value is a function of the distance from the wall to the first node (in the mesh you have) off the wall. Hence you can make this any value you like and thus won't have any connection with the boundary layer height.
RossFS is offline   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
Boundary layer calculation, scripting in Post. a.ob CFX 7 August 20, 2014 12:18
natural convection mehrdadeng CFX 10 February 25, 2011 06:25
CFX does not continue Shafiul CFX 10 February 17, 2011 08:57
Multicomponent fluid Andrea CFX 2 October 11, 2004 06:12
Wall boundary coordinates? cjtune Siemens 1 February 18, 2003 11:31


All times are GMT -4. The time now is 03:09.