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

Disabling Wall Functions

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

Like Tree1Likes
  • 1 Post By Kaskade

Reply
 
LinkBack Thread Tools Display Modes
Old   February 10, 2012, 07:10
Default Disabling Wall Functions
  #1
Member
 
Onno
Join Date: Jan 2012
Location: Germany
Posts: 93
Rep Power: 6
Kaskade is on a distinguished road
Hello,
I am trying to simulate a mesh containing walls with y+-Values between 100 and 200, as well as walls with y+-Values well below 1 using kOmegaSST.
Of course this is not really good to begin with but my idea was to use fixedValue for k and zeroGradient for omega on the walls with the low y+-Values.
Unfortunately when I start the simulation the OpenFOAM seems to set the walltypes to wallfunctions on it's own. Is there some way to disable this?
Kind regards
Kaskade
Kaskade is offline   Reply With Quote

Old   February 12, 2012, 14:59
Default
  #2
Member
 
Onno
Join Date: Jan 2012
Location: Germany
Posts: 93
Rep Power: 6
Kaskade is on a distinguished road
Answer:

k
type fixedValue;
value 0; //some say you should use a value like 1e-11, but it doesn't seem to make any difference

omega
type zeroGradient;

nut
type calculated;
value $internalField;

If you don't set up a file for nut yourself, OpenFOAM will generate it and upgrade your walls with wallfunctions.
slint likes this.
Kaskade is offline   Reply With Quote

Old   August 23, 2014, 04:30
Default
  #3
Senior Member
 
Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 266
Rep Power: 4
huangxianbei is on a distinguished road
Quote:
Originally Posted by Kaskade View Post
Answer:

k
type fixedValue;
value 0; //some say you should use a value like 1e-11, but it doesn't seem to make any difference

omega
type zeroGradient;

nut
type calculated;
value $internalField;

If you don't set up a file for nut yourself, OpenFOAM will generate it and upgrade your walls with wallfunctions.
Hi,Onno:
Why the nut is set to be calculated instead of zerogradient? I remember that when no wall function is needed, the type should be zerogradient. Please correct me if I'm wrong

Xianbei
huangxianbei is offline   Reply With Quote

Old   August 23, 2014, 04:48
Default
  #4
Member
 
Onno
Join Date: Jan 2012
Location: Germany
Posts: 93
Rep Power: 6
Kaskade is on a distinguished road
That was a long time ago.... right now I what say, you might as well leave the wall functions turned on and use nutUSpaldingWallFunction for nut.


@myself from 2,5 years ago: If your mesh is that bad/uneven -> fix that first.
Kaskade is offline   Reply With Quote

Old   August 23, 2014, 10:39
Default
  #5
Senior Member
 
Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 266
Rep Power: 4
huangxianbei is on a distinguished road
Quote:
Originally Posted by Kaskade View Post
That was a long time ago.... right now I what say, you might as well leave the wall functions turned on and use nutUSpaldingWallFunction for nut.


@myself from 2,5 years ago: If your mesh is that bad/uneven -> fix that first.
Hi,Onno:
Thank you for your reply. As omega based turbulence model can solve the finer mesh with y+<3 or less, so no wall function is needed when the mesh is fine enough. What do you mean by saying 'turn on the wall function as well'?

Xianbei
huangxianbei is offline   Reply With Quote

Old   August 23, 2014, 12:19
Default
  #6
Member
 
Onno
Join Date: Jan 2012
Location: Germany
Posts: 93
Rep Power: 6
Kaskade is on a distinguished road
In my original post I was asking for a way to turn of the wall function manually on walls with a small y+. But from I understand now, you don't need to turn off the wall functions, since omegaWallFunction and nutUSpaldingWallFunction can be used for small y+-values.
Kaskade is offline   Reply With Quote

Old   August 24, 2014, 02:03
Default
  #7
Senior Member
 
Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 266
Rep Power: 4
huangxianbei is on a distinguished road
Quote:
Originally Posted by Kaskade View Post
In my original post I was asking for a way to turn of the wall function manually on walls with a small y+. But from I understand now, you don't need to turn off the wall functions, since omegaWallFunction and nutUSpaldingWallFunction can be used for small y+-values.
I see, you mean it's a kind of automatic wall function similar to the commercial codes like CFX, right? Just not long before, I was confused about the wall function that there is no explicit y+ threshold in the source code. So the nuSgsWallFunction is similar to that of nutSpaldingwallfunction, which is also based on Spalding's law, right?
huangxianbei is offline   Reply With Quote

Old   August 24, 2014, 03:44
Default
  #8
Member
 
Onno
Join Date: Jan 2012
Location: Germany
Posts: 93
Rep Power: 6
Kaskade is on a distinguished road
It think it is discussed here: Compressible kOmegaSST
Kaskade is offline   Reply With Quote

Old   August 24, 2014, 09:53
Default
  #9
Senior Member
 
Huang Xianbei
Join Date: Sep 2013
Location: CAU,China
Posts: 266
Rep Power: 4
huangxianbei is on a distinguished road
Quote:
Originally Posted by Kaskade View Post
It think it is discussed here: Compressible kOmegaSST
Thank you very much. Now I know that the nut and nuSgs may be a generic wall function. So whatever the resolution of the mesh is , using a wall function will be better.
huangxianbei 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
Modelling Turbulent Wall Functions victorwfreire CFX 11 January 14, 2015 16:48
Wall functions - questions about implementation AlmostSurelyRob OpenFOAM 33 April 8, 2014 02:42
[ICEM] Export ICEM mesh to Gambit / Fluent romekr ANSYS Meshing & Geometry 1 November 26, 2011 13:11
Wall Functions pierre OpenFOAM Running, Solving & CFD 0 October 1, 2005 13:13
LES wall functions barrat Main CFD Forum 10 September 1, 2004 08:29


All times are GMT -4. The time now is 11:41.