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-   -   SYMMETRY + PERIODIC B.C....I need Help! (http://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.

please give me a suggestion!

thank you!

Andrew Garrard January 14, 2005 08:03

Re: SYMMETRY + PERIODIC B.C....I need Help!
 
If you specify your periodic boundary conditions in gambit correctly there should be an additional menu in define to allow you to set the mass flow rate. Don't change the B.C. from a periodic to a mass flow inlet.


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