# Symmetry Issue

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

 July 30, 2010, 13:09 Symmetry Issue #1 New Member   Dylan Kowalewski Join Date: Jun 2010 Posts: 8 Rep Power: 7 Hi I'm having a problem with the symmetry boundary condition on a combustion chamber in fluent. When I use it on my model, there appears to be a wall where the symmetry plane is (ie. two chambers instead of one). Any help would be appreciated.

 August 2, 2010, 01:24 #2 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,066 Rep Power: 31 does the plane appear with symmetry set-up in the BC list (in fluent)? __________________ In memory of my friend Hervé: CFD engineer & freerider

 August 3, 2010, 03:19 #3 New Member   Dylan Kowalewski Join Date: Jun 2010 Posts: 8 Rep Power: 7 Yes, the symmetry plane appears in the BC menu, but it seems to just calculate as if the half was one container, then just reflects that result over the plane.

August 3, 2010, 04:14
#4
Super Moderator

Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,066
Rep Power: 31
Quote:
 Originally Posted by dkowalewski then just reflects that result over the plane.
that's the definition of symmetry.
If your geometry is symmetric, and your BC are also symmetric. Then you split your geometry along its symmetry and you compute on one half, because you know that the result will be symmetric.
Purpous of use of symmetry is to save computationnal effort.
But maybe I didn't understand your problem
__________________
In memory of my friend Hervé: CFD engineer & freerider

 August 3, 2010, 05:58 #5 New Member   Dylan Kowalewski Join Date: Jun 2010 Posts: 8 Rep Power: 7 Yes, I'm splitting it in half to save computations, but there's a wall where the plane of symmetry is, so instead of having 1 chamber, I have 2. Is there any way to get rid of that?

 August 3, 2010, 06:17 #6 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,066 Rep Power: 31 if you split your domain along your symmetry, then you delete the volume you don't need. The closed volume remaining is "closed" by the symmetry plane (which is not considered as a wall... since it appears in fluent BC as symmetry). Can you post a picture? __________________ In memory of my friend Hervé: CFD engineer & freerider

August 3, 2010, 09:16
#7
New Member

Dylan Kowalewski
Join Date: Jun 2010
Posts: 8
Rep Power: 7
So here's a quick render I did of the setup. The line that goes straight down the centre is the plane of symmetry. There are three entrances for gases, side facing you and on the left and right sides. The pathlines are clearly following the plane of symmetry as if it were a wall.

Thanks
Attached Images
 symmetryproblem.jpg (57.7 KB, 7 views)

 August 3, 2010, 09:32 #8 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,066 Rep Power: 31 Per definition, on symmetry plane you shouldn't have velocity normal to the plane. In other words: on the symmetry you have V.n = 0 where n is the normal vector. So on symmetry you have only coplanar components and no normal component. If the pathlines go through the plane in the middle then your flowfield isn't symmetric (that's why I didn't call it symmetry since it is not mathematically correct) __________________ In memory of my friend Hervé: CFD engineer & freerider

 August 3, 2010, 09:35 #9 New Member   Dylan Kowalewski Join Date: Jun 2010 Posts: 8 Rep Power: 7 I see, so would this be reasonable to do if I did not have those inlets pointing towards the plane? Thanks for the help!

 August 4, 2010, 01:18 #10 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,066 Rep Power: 31 Are your Boundary Conditions also symmetric? __________________ In memory of my friend Hervé: CFD engineer & freerider

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post [ICEM] Blocking and Symmetry BrolY ANSYS Meshing & Geometry 32 August 24, 2012 03:13 Cirion0000 CFX 0 July 6, 2009 14:26 Matt CFX 2 February 25, 2009 06:41 Roland CFX 7 May 31, 2006 13:34 Deadly FLUENT 0 August 22, 2002 04:56

All times are GMT -4. The time now is 02:41.