
[Sponsors] 
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: 2,992
Rep Power: 30 
does the plane appear with symmetry setup 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: 2,992
Rep Power: 30 
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: 2,992
Rep Power: 30 
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 

August 3, 2010, 09:32 

#8 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 2,992
Rep Power: 30 
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: 2,992
Rep Power: 30 
Are your Boundary Conditions also symmetric?
__________________
In memory of my friend Hervé: CFD engineer & freerider 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
[ICEM] Blocking and Symmetry  BrolY  ANSYS Meshing & Geometry  32  August 24, 2012 03:13 
Properly using symmetry with both CFX and ANSYS workbench for a FSI analysis, help!  Cirion0000  CFX  0  July 6, 2009 14:26 
Forces in Symmetry  Matt  CFX  2  February 25, 2009 06:41 
Symmetry plane and force calculation  Roland  CFX  7  May 31, 2006 13:34 
Need desperate help again: Symmetry problem!!  Deadly  FLUENT  0  August 22, 2002 04:56 