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

Mesh size requirement

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 13, 2015, 16:04
Default Mesh size requirement
  #1
New Member
 
Sheng Zheng
Join Date: Oct 2015
Posts: 1
Rep Power: 0
shzheng is on a distinguished road
Hi all,

I'm a beginner of LES. I tried to perform an LES of turbulent flow in a pipe. However, I observed that the fluctuations in velocity disappear after a substantial period of time. I googled about this and read that this might be due to the size of the mesh being too large. I was wondering if anyone can confirm this and also wondering what will be a good rule of thumb for determining mesh size. Thanks!
shzheng is offline   Reply With Quote

Old   October 14, 2015, 00:45
Default
  #2
Senior Member
 
Lucky Tran
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 940
Rep Power: 16
LuckyTran will become famous soon enough
If your numerical diffusion is high then flow can re-laminarize (but you'd have to be doing really poor LES). What's more common is people don't know that you have to add initial perturbations to the velocity field in order to get a turbulent result. So did you remember to do this?

For pipe flows grid resolution is fairly straight forward. You use the usual 16 pts across the boundary layer (32 across the diameter). Or you can increase to 32/64, etc. What's severely limiting is near wall resolution (i.e. y+ <1). If you achieve your wall y+ requirement for whatever model you are using, and use a small stretch ratio then your grid resolution should be at least in the right ballpark.
LuckyTran is offline   Reply With Quote

Reply

Tags
les, mesh size

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
dynamicTopoFVMesh and pointDisplacement RandomUser OpenFOAM Meshing & Mesh Conversion 5 March 2, 2015 18:19
engrid -> save as .stl with boundarie codes Zymon enGrid 31 August 29, 2011 13:40
snappyHexMesh won't work - zeros everywhere! sc298 OpenFOAM Native Meshers: snappyHexMesh and Others 2 March 27, 2011 21:11
How to decide the mesh size? echo CD-adapco 1 May 23, 2006 05:34
How to control Minximum mesh space? hung FLUENT 7 April 18, 2005 09:38


All times are GMT -4. The time now is 03:56.