# symmetry vs periodicity

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April 2, 2014, 09:41
symmetry vs periodicity
#1
Senior Member

Join Date: Jul 2010
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Hello all.

I have a problem and I don't know how to model it correctly. On the picture you can see two domains. The one transparent is static domain and the yellow one is rotating. At the top of the static domains there is air inlet and on both sides there is air outlet. I think that I can't use both (symmetry on static domain and rotational periodicity on rotating domain) however static domain is symmetric. And I think that I can't use symmetry for rotating domain. Am I correct?

Can someone help me please with this problem?

Regards
Attached Images
 sym1.jpg (23.3 KB, 24 views) sym2.jpg (17.4 KB, 15 views)

April 2, 2014, 10:50
#2
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Bruno
Join Date: Mar 2009
Location: Brazil
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Quote:
 Originally Posted by keeper I have a problem and I don't know how to model it correctly. On the picture you can see two domains. The one transparent is static domain and the yellow one is rotating. At the top of the static domains there is air inlet and on both sides there is air outlet. I think that I can't use both (symmetry on static domain and rotational periodicity on rotating domain) however static domain is symmetric. And I think that I can't use symmetry for rotating domain. Am I correct?
I'm taking that the red, green and blue arrows are X, Y and Z (as used by DM and Meshing).

The problem with your current geometry is that, because of the rotating domain, the flow isn't symmetric in the XY plane, making your geometry not representative of the flow you're trying to model. But if both outlets have the same operating condition what you can do, however, is use a symmetry for both domains in the XZ plane. The size of your problem should be roughly the same.

Cheers

 April 3, 2014, 02:12 #3 Senior Member   Join Date: Jul 2010 Posts: 152 Rep Power: 16 In fact this is very simple representation of my real model but idea is just like that. So you mean there is no chance to have only 180deg model? Do I really have to model full 360deg model? Thank you.

April 3, 2014, 04:10
#4
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Quote:
 Originally Posted by keeper In fact this is very simple representation of my real model but idea is just like that. So you mean there is no chance to have only 180deg model? Do I really have to model full 360deg model? Thank you.
As brunoc mentioned, you can slice your geometry by plane which is parallel to your inlet. This also will give you half of full geometry.

 April 3, 2014, 04:15 #5 Senior Member   Join Date: Jul 2010 Posts: 152 Rep Power: 16 As I said this is not real complex geometry that I actually have so I can't split it as mentioned above. Let's say that each inlet has different BCs.

April 3, 2014, 04:19
#6
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Quote:
 Originally Posted by keeper As I said this is not real complex geometry that I actually have so I can't split it as mentioned above. Let's say that each inlet has different BCs.
Then there is no symmetry or periodicity