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

Wall boundary conditions for turbulence models

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 18, 2013, 02:56
Default Wall boundary conditions for turbulence models
  #1
New Member
 
steve
Join Date: Sep 2012
Posts: 15
Rep Power: 4
greenleader is on a distinguished road
CFD + OpenFOAM Newbie question:
I'm confused about how to specify boundary conditions on walls for turbulence models.
(I have looked through the manuals, the forums and examples, and sadly I'm still confused!)

Can anyone offer a concise explanation of the entries that should be specified in the /0/k /0/epsilon and /0/omega dictionaries, and the general approach to selecting values of k/epsilon/omega on the walls?

(I am reasonably happy with how to set up the inlet/outlets, but I am struggling with the walls!)

The specific case I am working on is a circular duct with air flowing over an obstacle in the duct. Initially I want to use wall functions.

I see things like this in the examples:
Code:
    DuctWalls
    {
        type            omegaWallFunction;
        value           $internalField;
    }
or
Code:
   DuctWalls
    {
        type            epsilonWallFunction;
        value           uniform 0.01;
    }
What's the difference between value $internalField and value uniform? What do these keywords tell OF to do? Sometimes I see the value set to uniform 0.0 other times to some value.

If I wanted to do the near-wall approach and not use wall functions, what would I do differently in setting these parameters?

Any comments are appreciated....
greenleader is offline   Reply With Quote

Old   May 18, 2013, 23:55
Default
  #2
Member
 
Eric R
Join Date: Jul 2012
Location: Mississippi State University
Posts: 73
Rep Power: 5
msuaeronautics is on a distinguished road
The $internalField keyword is essentially telling OF that you would like that particular boundary to take on the value that is specified next to the "internal field" closer to the top of the file. The "internal field" value is just a starting parameter describing what's going on inside the domain just before the simulation begins, and gets overwritten at the first step. It is normally acceptable to use 0 for this.

If I'm not mistaken, you should use large values of omega at the walls (in the thousands). The uniform keyword allows you to specify a particular value (essentially saying that the value you specify is uniform across that entire boundary and that there is no gradient or any type of variation).
msuaeronautics is offline   Reply With Quote

Old   May 27, 2013, 10:01
Default
  #3
New Member
 
steve
Join Date: Sep 2012
Posts: 15
Rep Power: 4
greenleader is on a distinguished road
Sorry msuaeronautics, I missed your reply... thanks for your comments.
greenleader 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
Low Mixing time Problem Mavier CFX 5 April 29, 2013 00:00
Error finding variable "THERMX" sunilpatil CFX 8 April 26, 2013 07:00
Domain Imbalance HMR CFX 3 March 6, 2011 21:10
natural convection mehrdadeng CFX 10 February 25, 2011 06:25


All times are GMT -4. The time now is 16:25.