CFD Online Logo CFD Online URL
Home > Forums > FLUENT

Non Equilibrium

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

LinkBack Thread Tools Display Modes
Old   August 24, 2008, 13:22
Default Non Equilibrium
Posts: n/a
I want to know why the wall treatment Non Equilibrium need an Y+ > 30? and what does it do when Y+<10?

Thanks in advance
  Reply With Quote

Old   August 28, 2008, 15:37
Default Re: Non Equilibrium
Jason B
Posts: n/a
I recommend doing some research on boundary layers and the component layers of a boundary layer.

The non-equilibrium treatment assumes you're in the log-layer of fluid. Below y+ of 30 the boundary layer profile does not follow a logarithmic shape and therefore the log-layer assumption is not valid. The code will calculate the flowfield for any y+ values (around y+ of 11 it switches from a log calculation to a linear calculation... don't quote me on the exact transition point, I'm a bit rusty, but know that at some point it switches how it's calculating). But in real boundary layers the non-dimensionalized velocity distribution is approximately linear below y+ of 5, and then from 30 to 300 it's logarithmic. Between 5 and 30 is the "buffer layer" which is poorly defined (although there have been emperical curve fits and such, few tools take advantage of these, including Fluent). It's recommended that you size your mesh so that your first cell does not fall in this region. You can either tighten mesh and switch to enhanced wall treatments (y+ ~ 1) or losen your mesh (shooting for y+ ~ 30 or above).

Hope this helps, and good luck, Jason
  Reply With Quote


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
How to set an equilibrium-Air model jorge sancho CFX 4 August 24, 2015 06:32
equilibrium between phases chouki FLUENT 1 August 27, 2008 17:29
chemical equilibrium George Main CFD Forum 5 October 3, 2007 06:29
Non-Equilibrium log-law wall Sima Baheri Phoenics 2 October 3, 2006 02:52
Non-Equilibrium log-law? Sima Baheri Phoenics 0 June 5, 2006 12:49

All times are GMT -4. The time now is 05:36.