CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Minimum Recommended Yplus High-Re Turbulence Models

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 16, 2013, 08:57
Default Minimum Recommended Yplus High-Re Turbulence Models
  #1
Member
 
Join Date: Apr 2009
Posts: 36
Rep Power: 8
minger is on a distinguished road
Hi All -- relative beginner OpenFoam user.

I am attempting some numerical validation of a geometry with a tight gap/clearance. I was initially running the Low-Re LaunderSharma k-epsilon model with fully resolved boundary layers; maximum yplus of 1.

However, for unsteady and LES simulations, my required timestep for stability is incredibly small -- ~2 orders of magnitude smaller than what'd I'd like it.

So, I decided to abandon the idea of fully resolved viscous sublayers and use a wall function approach -- which I'm familiar with in the commercial world. However, I am struggling to get a mesh "coarse" enough for ensure my first cell lies in the logarithmic region.

If this were Fluent, I would switch on "scalable" or "enhanced" wall treatment to account for this. Knowing that this doesn't seem to be an option, is there is a lower recommended limit for Yplus using OpenFoam wall functions?

My average on my walls of interest is ~9, which my experience tells me is too low for standard wall function treatment, but I'm scared if I go any coarser I will lose ability to resolve flow through the gap properly.
minger is offline   Reply With Quote

Old   August 16, 2013, 09:19
Default
  #2
New Member
 
Kumar
Join Date: Jun 2013
Posts: 15
Rep Power: 4
kishpishar is on a distinguished road
Hi,

Although the normal recommended practice of wall y plus is somewhere between 30 and 500 (limits of log-law layer) for the wall function approach to work well, I remember having read somewhere that the conventional wall function approach may be used up to a y+ lower limit of 11 or so. This might result in reduced accuracy but how much it spoils the solution fidelity might be case-dependent.

If you already have an averge y+ of around 9, perhaps you could coarsen a them a bit more and try it out.
kishpishar is offline   Reply With Quote

Old   August 16, 2013, 09:29
Default
  #3
New Member
 
Andreas
Join Date: Aug 2013
Posts: 8
Rep Power: 4
docinger is on a distinguished road
This depends on the wallfunctions, some are capable to work well in the viscous sublayer, low y+ region, but none work well in the region between 5<y+<20, where you are right in with y+=9

http://en.wikipedia.org/wiki/Law_of_the_wall
docinger 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
in k-epsilon wall function approach high Re turbulence models: question of velocity romant OpenFOAM Programming & Development 5 March 15, 2015 22:12
Turbulence models become invalid at Re=2000~5000? liweif FLUENT 9 August 27, 2007 11:55
high discrepancies among similar models Atit Koonsriusk CFX 5 September 6, 2006 17:10
turbulence models? haider FLUENT 0 March 8, 2006 00:58
How to set phase dependent turbulence models? J.Yang CFX 2 August 29, 2002 15:39


All times are GMT -4. The time now is 00:26.