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April 17, 2012, 00:06 
what's the different between SYMMETRY and AXIS

#1 
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Zhonghai Xu(xuzhonghai@sjtu.edu.cn)
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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

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. 

April 17, 2012, 06:00 

#3 
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Zhonghai Xu(xuzhonghai@sjtu.edu.cn)
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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


April 17, 2012, 06:21 

#5 
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Zhonghai Xu(xuzhonghai@sjtu.edu.cn)
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April 17, 2012, 06:36 

#6 
Super Moderator

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. 

April 17, 2012, 06:41 

#8 
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Zhonghai Xu(xuzhonghai@sjtu.edu.cn)
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It's kind of you.
thanks very much~ 

February 14, 2013, 13:10 

#9  
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BENMENZER SOUFYANE
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Quote:
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 please help me 

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