# Rotational periodic boundary condition

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 April 19, 2012, 09:09 Rotational periodic boundary condition #1 New Member   Helen Join Date: Apr 2012 Posts: 17 Rep Power: 7 Hello. How do you think if I model the flow inside such two domains as: 1) the whole domain (360 degrees), containing, for example, 20 rotational periodic repeated parts 2) the domain (18 degrees), which is the sector 1/20 of the domain 1, using the rotational periodic boundary condition will the results identical??? I'll be thankful for yours comments PS. Sorry for my english

April 19, 2012, 09:44
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Lucky Tran
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Quote:
 Originally Posted by oborona Hello. How do you think if I model the flow inside such two domains as: 1) the whole domain (360 degrees), containing, for example, 20 rotational periodic repeated parts 2) the domain (18 degrees), which is the sector 1/20 of the domain 1, using the rotational periodic boundary condition will the results identical??? I'll be thankful for yours comments PS. Sorry for my english
It depends on what you're trying to do and what you're interested in.

The answer is not always. It will depend on the flow. It is definitely worth a shot to try it on the reduced domain though.

Do you expect the flow in all 20 parts to be exactly the same? If yes, then yes you can model 1/20. If no, then do the full 20/20. An instability may arise in one or more of the parts and move through the domain, use of periodic boundary conditions would otherwise kill these structures.

 April 19, 2012, 10:49 #3 New Member   Helen Join Date: Apr 2012 Posts: 17 Rep Power: 7 Thank you. All 20 parts of the domain are the same, so I modeled 1/20 part using periodic boundary condition. But satisfying my interest I modeled whole domain (360 degrees) and I got the periodic flow field, but this flow field is differ from the 1/20. But I thought that results will be similar ...

April 19, 2012, 10:56
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Lucky Tran
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Quote:
 Originally Posted by oborona Thank you. All 20 parts of the domain are the same, so I modeled 1/20 part using periodic boundary condition. But satisfying my interest I modeled whole domain (360 degrees) and I got the periodic flow field, but this flow field is differ from the 1/20. But I thought that results will be similar ...
The time-averaged statistics should be identical if solved correctly.
If you are doing steady RANS, they should be identical.

 April 19, 2012, 11:47 #5 New Member   Helen Join Date: Apr 2012 Posts: 17 Rep Power: 7 I think the same way. But I don't know how to explain my results. (((

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