CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > ANSYS Meshing & Geometry

[ICEM] Boundary Layer Thickness

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

Like Tree1Likes
  • 1 Post By siw

Reply
 
LinkBack Thread Tools Display Modes
Old   September 12, 2012, 04:41
Default Boundary Layer Thickness
  #1
Joh
New Member
 
Joh
Join Date: Sep 2012
Posts: 6
Rep Power: 4
Joh is on a distinguished road
Dear all,
How can you assess if the boundaries are sufficiently big enough to deal with your flow? So for unstructured mesh, how do you know how many prism layers to use. I use 3, split them into 6 and then rearrage them with a ratio of 1.4 and it seems to work. But how confident can I be that this will give the right results?
Regards,
Joh
Joh is offline   Reply With Quote

Old   September 12, 2012, 08:27
Default
  #2
siw
Senior Member
 
Join Date: Jul 2009
Posts: 446
Rep Power: 14
siw will become famous soon enough
In answer to your question, you will need to conduct a simulation to see if the results are physically sensible/what you expect/match other sources of data. Only then can you know if the modelling of the boundary layer etc with your chosen generation of prisms was okay. If not you'll then have to make some mesh changes and repeat. Personally, I keep the expansion ratio to 1.2 or lower. Also, if using CFX (so I know it's in the manuals) but probably FLEUNT aswell it recommends 10 to 15 layers for RANS simulations and the y+ depending on the turbulence model and near wall treatment of choice.
siw is offline   Reply With Quote

Old   September 12, 2012, 09:34
Default
  #3
Joh
New Member
 
Joh
Join Date: Sep 2012
Posts: 6
Rep Power: 4
Joh is on a distinguished road
Thanks, why do you keep the expansion ratio to 1.2 or lower?
What about for structured meshes, how do you know how far the O-ring has to be placed for laminar flow? Is it the same idea? Run the mesh and see if it gives a plausible solution?
Joh is offline   Reply With Quote

Old   September 13, 2012, 08:37
Default
  #4
siw
Senior Member
 
Join Date: Jul 2009
Posts: 446
Rep Power: 14
siw will become famous soon enough
1.2 is the default value in ANSYS Meshing and it is the recommended value I've found in various user manuals, reports etc. However, sometimes I use lower values, but not hgher values. Give it a try and see how/if your results are dependent upon the value.

Again for the O-grid question, you'll only know once you've tried some different lengths for your particular simulation and its effect. I find with mesh generation, you just have to make what you judge to be a reasonable mesh for your simulation (to as best a quality as you can get it) and then run the simulation and repeat from there as you think best.
PSYMN likes this.
siw is offline   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
No layers in a small gap bobburnquist OpenFOAM Native Meshers: snappyHexMesh and Others 6 August 26, 2015 09:38
Questions about Boundary Layer Thickness and Turbulence Models famerfamer STAR-CCM+ 3 July 12, 2012 09:47
Boundary Layer roughness/ low reynolds wall treatment Luigi_ STAR-CCM+ 1 March 14, 2012 09:40
Boundary layer thickness ghazanfarzahedi Main CFD Forum 2 July 28, 2009 23:43
errors Fahad Main CFD Forum 0 March 23, 2004 14:20


All times are GMT -4. The time now is 18:24.