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-   -   SYMMETRY + PERIODIC B.C....I need Help! (https://www.cfd-online.com/Forums/fluent/35405-symmetry-periodic-b-c-i-need-help.html)

 JB January 7, 2005 09:39

SYMMETRY + PERIODIC B.C....I need Help!

Hi there!

In order to simplify my 3D model, i'd like to use both Periodic and Symmetry Boundary Conditions with Gambit: here are the steps I want to follow: 1.creation of my reduced 3D model. 2.on one side of the model : symmetry BC applied. 3 on the other side: periodic BC applied.

entire model (2D view):

/\/\/\/\/\/\/\/\/\/ ...

my model:

periodic--> / <--symmetry

does anyone know if this would work?

thanks a lot!

 Andrew Garrard January 7, 2005 10:32

Re: SYMMETRY + PERIODIC B.C....I need Help!

As far as I am aware, a periodic boundary needs to have a partner that is identically meshed. This is because the solution variables, such as velocity and temperature, are mirrored on each face.

If you model has the zig-zag pattern you mention, then you could use two periodic boundarys, one for inlet and one for outlet, if the flow is parallel to the zig-zag

\/\/\/\/\/\/\/\/\/

------->

This would have the effect of modeling an infinatly long section with a repeating pattern as above.

BTW. are you working on MR fluids?

 JB January 7, 2005 10:37

Re: SYMMETRY + PERIODIC B.C....I need Help!

Thank you andrew...My flow is normal to the zigzag, but anyway, I bet you're right!..I'm screwed :(

What is MR fluid? is that a software?

 Andrew Garrard January 7, 2005 10:45

Re: SYMMETRY + PERIODIC B.C....I need Help!

If you don't know what it is, you won't be working on it. I just used to know a guy who worked on some zig-zag geometry like that, I thought it might be the same.

So you flow is normal to, but away from the zig-zag. So it is the inlet then? You might still be able to use a periodic boundary condition, or a symmetry one. depending on what you fluid structure you are trying to capture. Basically if you use a periodic you are repeating boundary condition so that the they have the same values on. The clasic example is a long pipe. You model a small section and say the inlet and outlet are periodic. A symetry boundary is exactly what it says on the tin. Basically if you have a symetrical geometry and boundary conditions you can chop it in half and mirror the results. If you want more advice on your problem we will have to have a better idea of what you are trying to model. You might have to host a picture on a website.

 JB January 7, 2005 11:29

Re: SYMMETRY + PERIODIC B.C....I need Help!

Actually I'm currently working on heat exchangers (engine cooling). I'll try to send you a more explicit picture of my model, but the more I think about it, the more I think it's impossible to use both Symmetry and Periodic BC in my case. thanks for your help! jb

 Lcw January 7, 2005 23:33

Re: SYMMETRY + PERIODIC B.C....I need Help!

I have a question: How can I simulate a pipe flow using PERIODIC B.C? I ever have a try, but failed. My steps are: 1.plot a part of pipe, link the front face with back face; 2.plot mesh; 3.specify BC as PERIODIC,produce a .msh file; 4.introduce .msh file to FLUENT; 5.specify mass flow rate BC; 6.iterate computation.