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

symmetry and wall (free slip) BC

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 11, 2012, 03:10
Default symmetry and wall (free slip) BC
  #1
Member
 
Hamed Abdul Majeed
Join Date: May 2012
Posts: 76
Rep Power: 6
hamed.majeed is on a distinguished road
Hi,
What is the difference between symmetry and free slip wall boundary conditions in ANSYS CFX.
hamed.majeed is offline   Reply With Quote

Old   October 11, 2012, 05:56
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,638
Rep Power: 98
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
This is described in the documentation.

Symmetry enforces zero normal gradient to all parameters, and a slip wall does not necessarily do this. But for most normal simulations they are equivalent.

And a symmetry plane is required to be planar, but a slip wall can be any shape.
ghorrocks is offline   Reply With Quote

Old   August 20, 2015, 13:31
Default
  #3
Far
Super Moderator
 
Sijal
Join Date: Mar 2009
Location: Islamabad
Posts: 4,285
Blog Entries: 6
Rep Power: 43
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
@ghorrocks : Some body showed a case of cylindrical shape domain and he has applied symmetry condition for the 60 deg sector. In my understanding symmetry condition reflect the solution around the mirror plane which in my understating can only be applied to two planes in 3-d case. I suggested him the periodic bc instead.

What do you think?
Far is offline   Reply With Quote

Old   August 20, 2015, 13:47
Default
  #4
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 1,266
Rep Power: 22
flotus1 will become famous soon enoughflotus1 will become famous soon enough
I did not double-check if this is true in CFX. Another difference between the two boundary types should show up when using a turbulence model.
Near a free-slip wall, the turbulence kinetic energy is zero while at a symmetry boundary condition its normal gradient is zero.
flotus1 is offline   Reply With Quote

Old   August 20, 2015, 13:54
Default
  #5
Far
Super Moderator
 
Sijal
Join Date: Mar 2009
Location: Islamabad
Posts: 4,285
Blog Entries: 6
Rep Power: 43
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
Quote:
Originally Posted by flotus1 View Post
I did not double-check if this is true in CFX. Another difference between the two boundary types should show up when using a turbulence model.
Near a free-slip wall, the turbulence kinetic energy is zero while at a symmetry boundary condition its normal gradient is zero.
If any boundary (wall) is not generating turbulence, will it affect ?? in that case both will behave in similar manner?

This is taken from CFX help :

Quote:
For turbulent flows, the specified shear is applied directly; no considerations about turbulent wall functions are taken into account.
Far is offline   Reply With Quote

Old   August 20, 2015, 14:02
Default
  #6
Far
Super Moderator
 
Sijal
Join Date: Mar 2009
Location: Islamabad
Posts: 4,285
Blog Entries: 6
Rep Power: 43
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
and this is from the fluent help (same meaning as shown in CFX help ) and which is very much clear...



Fluent help on symmetry BC:

Attached Images
File Type: jpg Untitled.jpg (17.8 KB, 281 views)
File Type: jpg Untitled3.jpg (23.8 KB, 271 views)
Far is offline   Reply With Quote

Old   August 20, 2015, 18:16
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,638
Rep Power: 98
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
Quote:
In my understanding symmetry condition reflect the solution around the mirror plane which in my understating can only be applied to two planes in 3-d case. I suggested him the periodic bc instead.
A symmetry boundary has zero normal flow. So that means no swirl. A periodic boundary allows normal flow so can allow swirl.

That is the key difference to keep in mind for symmetry versus periodic.
ghorrocks 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
slip wall boundary condition mb.pejvak Main CFD Forum 5 May 24, 2014 06:49
Radiation interface hinca CFX 15 January 26, 2014 18:11
Wall functions with symmetry moser_r OpenFOAM Running, Solving & CFD 9 August 30, 2012 09:11
Modelling free surfaces using no slip wall, and other general queries andy_mckay88 Main CFD Forum 1 November 18, 2010 06:54
wall and symmetry boundary conditions malik FLUENT 2 April 22, 2008 07:48


All times are GMT -4. The time now is 05:18.