# [ICEM] what's the different between SYMMETRY and AXIS

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 April 17, 2012, 00:06 what's the different between SYMMETRY and AXIS #1 New Member   Zhonghai Xu(xuzhonghai@sjtu.edu.cn) Join Date: Apr 2012 Location: Shanghai,CHINA Posts: 17 Rep Power: 5 what's the different between SYMMETRY and AXIS I calculated a simulation model by Fluent,but when I used symmetry(boundary condition) it turn out ERROR:divergence AMG solver! I decreased the presure relaxation factor ,but failed again.So I converted the boundary condition into AXIS,the problem solved,I confused. thanks a lot~

 April 17, 2012, 04:29 #2 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,914 Blog Entries: 6 Rep Power: 38 Symmetry : It is used to reduce the computational model in 3D. For example if you have rectangular box then you can model 1/2 or 1/4 by using the one or two symmetry planes respectively. Axis: It is used to model the 3D problem by just taking the one plane and then solving it in the cylindrical coordinates. So for x and y, you solve the problem in r coordinates (r 2 = x2 + y2) and for Z you use the axial coordinates. This is only valid for domain with circular periphery. realstoneman likes this.

 April 17, 2012, 06:00 #3 New Member   Zhonghai Xu(xuzhonghai@sjtu.edu.cn) Join Date: Apr 2012 Location: Shanghai,CHINA Posts: 17 Rep Power: 5 Thank you for your reply My simulation model is a ejector(2D),which contains a main inlet,an second inlet and an outlet,I set up the boundary condition as Symmetry at first,it turned out wrong,and Axis is right.as you said above,it's OK for both,why shouldn't I choose Symmetry?

April 17, 2012, 06:11
#4
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Zhonghai Xu(xuzhonghai@sjtu.edu.cn)
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here is the model
Attached Images
 ejector.jpg (90.0 KB, 36 views)

 April 17, 2012, 06:21 #5 New Member   Zhonghai Xu(xuzhonghai@sjtu.edu.cn) Join Date: Apr 2012 Location: Shanghai,CHINA Posts: 17 Rep Power: 5

 April 17, 2012, 06:36 #6 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,914 Blog Entries: 6 Rep Power: 38 Symmetry is used for the 3D model to reduce the mesh size and model still remains 3D. Axis condition tells the solver that now activate the axisymmetric model and it is 2d model and uses 2d solver. Axis is always defined at axis of geometry. PSYMN likes this.

April 17, 2012, 06:38
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Quote:
 Originally Posted by realstoneman here is the model
This is 2d planner section of 3d and therefore is candidate of axis condition.

 April 17, 2012, 06:41 #8 New Member   Zhonghai Xu(xuzhonghai@sjtu.edu.cn) Join Date: Apr 2012 Location: Shanghai,CHINA Posts: 17 Rep Power: 5 It's kind of you. thanks very much~

February 14, 2013, 13:10
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BENMENZER SOUFYANE
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Quote:
 Originally Posted by realstoneman what's the different between SYMMETRY and AXIS I calculated a simulation model by Fluent,but when I used symmetry(boundary condition) it turn out ERROR:divergence AMG solver! I decreased the presure relaxation factor ,but failed again.So I converted the boundary condition into AXIS,the problem solved,I confused. thanks a lot~
yes ,I have the same probleme with fluent when I set the solver

it must to turn the symmetry condition to axis

but I dont solved it because ,I have a divergence solution

can you hep me what's the solver must used, and can you send me your file ejector.cas