# Periodicity in ICEM

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 January 12, 2009, 14:53 Periodicity in ICEM #1 James Guest   Posts: n/a Hi, I'm afraid this is a long post as I need to explain what I am trying to do in detail. Please bear with me. I have done a Hexa mesh on an axisymmetric geometry using ICEM. I only use an angular segment since it's axisymmetric. The two periodic surfaces need to be in separate parts for the in-house CFD code I'm using, this is to set upper and lower boundary conditions on the surfaces. When I try to load this mesh it gives an error stating that I have the wrong number of faces. I then did another mesh without setting up periodicity but still using the same angular segment (this is obviously wrong but I wanted to see what the code gives now). This mesh does not give an error while loading. However it later identified that the two periodic faces I defined had different number of nodes, hence did not work. I created a third mesh in which I set up periodicity again, but this time the two periodic surfaces were put in a single part. This mesh loaded without any problem, but as I mentioned earlier I cannot set the boundary conditions since it's one part. There must be something wrong with my mesh. I've done the mesh several times now and I can't figure out what the problem is. Can anyone please suggest anything else I could try? Thanks

 January 13, 2009, 01:19 Re: Periodicity in ICEM #2 carno Guest   Posts: n/a Why you want to keep the two parts. If there is a requirement the periodicity is not possible with two periodic faces on two different parts. It is not correct. Study a bit how periodicity works. For example it changes the tangential vectors by the angle of periodicity and applies to other face (and many more things). That means the two faces are connected through periodic BC. They have to be in one part. Do you think this is possible when there are two parts involved in single periodicity? What is the purpose of periodicity then? Hope you are not talking about symmetry which is different.

 January 13, 2009, 04:33 Re: Periodicity in ICEM #3 James Guest   Posts: n/a Thank you for the reply. I am fairly certain I have to use periodicity for my geometry. I'm new to all this meshing stuff and I have to agree that it does not make sense that I could have periodicity when there are two different parts. The only reason I set up periodicity is because when I load the mesh in my CFD program it only recognizes the parts that contains surfaces as boundaries. So if I have two faces in one part it considers it to be a single boundary. I can easily define the boundary condition for the TOPWALL, INLET and OUTLET. But if I put the two periodic surfaces in a single part called 'SIDES' then I can't seem to find any boundary conditions that I can apply to it. The only boundary conditions for periodicity are called 'Upper periodic boundary' and 'Lower periodic boundary' which needs two separate parts.

 January 13, 2009, 15:20 Re: Periodicity in ICEM #4 James Guest   Posts: n/a I've found the problem is that the solver does not like it when the two periodic faces meet at the axis. I had to have a finite face at the location where they meet.

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