# [ICEM] Can I define periodic boundaries in an unstructured mesh?

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 May 28, 2012, 12:19 Can I define periodic boundaries in an unstructured mesh? #1 New Member   Kora Join Date: Nov 2011 Posts: 11 Rep Power: 13 Hi all. I'm modelling a tidal stream turbine. To reduce the size I only built 1/3 of the turbine with periodic boundaries. I defined periodicity in global mesh parameters and generated the mesh. But when I read it in FLUENT it can only recognise one of the periodic boundaries. I've read a few threads regarding to periodic boundaries, and it seems that to define a periodic boundary I would need to define the periodic vertices from the corresponding block after I define periodicity in global mesh parameters. Is that the reason why my mesh doesn't work properly? However, I'm currently doing an unstructured mesh and it doesn't have any blocking. Does it mean that I cannot define periodic boundaries on an unstructured mesh? Are there other ways to work round it? Thanks in advance.

 June 13, 2012, 09:01 #2 Member   Yon Han Chong Join Date: Jun 2012 Posts: 77 Rep Power: 12 I am not sure what you are trying to do but you can do periodic boundary with unstructed mesh.

June 13, 2012, 09:38
#3
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Kora
Join Date: Nov 2011
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Quote:
 Originally Posted by yonchong I am not sure what you are trying to do but you can do periodic boundary with unstructed mesh.
Thanks. Well, this is what I was trying to mesh.

I don't know what's wrong with it. I checked the mesh, which doesn't seem to have any problem. But when I try to solve it in fluent it diverge straight away. I was told that there should be two faces for the periodicity but when I important it into fluent it could found recognise the top one.

 June 13, 2012, 09:50 #4 Member   Yon Han Chong Join Date: Jun 2012 Posts: 77 Rep Power: 12 Recognizing the only one side is normal. Why don't you run one iteration and check the solution. You could also try the fmg-initialization and check the solution. You have to refer to the manual for this as this option is only available through Text User Interface. However, it could give you very good initial guess of the solution. If the fmg-initalization fails I would check your boundary condition again including the periodic axis definition in fluid domains. Fluid might be cyclic in an wrong axis.

 June 16, 2012, 14:21 #5 Member   Khayyamian Join Date: Dec 2010 Posts: 46 Rep Power: 14 Hi, If you are working with ICEM go to view menu and Mirrors and replicates, and generate the 2nd part of the mesh and you can check manually that your nodes are matching (i.e. conformal mesh) Also check your mesh in the edit mesh tab . this is very useful! In your fluent did you set periodic boundary condition?

June 19, 2012, 10:24
#6
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Kora
Join Date: Nov 2011
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Rep Power: 13
Quote:
 Originally Posted by hadikhayyamian Hi, If you are working with ICEM go to view menu and Mirrors and replicates, and generate the 2nd part of the mesh and you can check manually that your nodes are matching (i.e. conformal mesh) Also check your mesh in the edit mesh tab . this is very useful! In your fluent did you set periodic boundary condition?
In ICEM I have checked the mesh and I didn't find any problem.

In FLUENT I only set periodicity as rotational at boundary condition. Are there anything else that I need to set up in FLUENT? This is the first time for me to set up a periodic boundary condition, I might have missed something that I didn't know about.

 June 19, 2012, 10:35 #7 Member   Khayyamian Join Date: Dec 2010 Posts: 46 Rep Power: 14 However there are other advanced settings, I guess thats fine. now, what is your problem?

June 19, 2012, 10:43
#8
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Kora
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Quote:
 Originally Posted by hadikhayyamian However there are other advanced settings, I guess thats fine. now, what is your problem?
My problem is that it deverged straight away in the first iteration.

Divergence detected in AMG solver: pressure correction
Divergence detected in AMG solver: k
Primitive Error at Node 0: floating point exception
Primitive Error at Node 1: floating point exception
Primitive Error at Node 2: floating point exception
Primitive Error at Node 3: floating point exception
Error: floating point exception
Error Object: #f

I've never seen something like this happened before so I don't even know which bit of it is wrong: whether is the mesh or the setting in FLUENT.

 June 19, 2012, 11:38 #9 Member   Yon Han Chong Join Date: Jun 2012 Posts: 77 Rep Power: 12 You need to set the rotational-axis direction. Cell Zone Conditions -> Zone, Edit As I said, stop or write out after few interations to check the boundary conditions. hadikhayyamian likes this.

 June 19, 2012, 12:34 #10 New Member   Kora Join Date: Nov 2011 Posts: 11 Rep Power: 13 Hi guys, thanks very much for your help and information. The model is working now. Probably because I missed defining the axis. Thanks again.

 August 1, 2013, 21:57 Translational periodic condition in icem cfd #11 New Member   Rijas Join Date: Aug 2013 Posts: 5 Rep Power: 11 Hi could any one tell me how to set translatinal periodic condition for a cascade airfoil?

September 14, 2018, 01:52
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Quote:
 Originally Posted by Aoki Hi guys, thanks very much for your help and information. The model is working now. Probably because I missed defining the axis. Thanks again.
hi dear i am also doing something very similar right now i need to know that just defining periodicity and axis in global mesh parameters( axis + angle) would suffice creating two periodic sides ( as you did i am also working on a turbine similar to this one) ? Or i need to define periodic vertices ( how to do that if i had to do that) ? Please reply please

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