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Define value at symmetry channel

Posted Jan 25, 2012, 11:35 a.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.2 3 Replies

Rui Silva
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Hi folks,

this is probably a simple question but I can't seem to figure it out...

I am using a 2D channel define between two plates, and I was wondering if it is possible to
define a value for the symmetry of this system.

In other words, is ti possible to define dk/dx =0 at the middle of the flow?

Best Regards,

Rui Silva
3 Replies Last Post Jan 25, 2012, 4:09 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 25, 2012, 2:58 p.m. EST
Hi

but isnt thta cutting your geoemtry in 2 and apply a symmetry condition on that wall ?
I assume your flow is "vertical, along y, or have I missed a point.

In anycase take a look at the equations COMSOL uses for a symmetry plane that should inspire you to write your own weak constraint
--
Good luck
Ivar
Hi but isnt thta cutting your geoemtry in 2 and apply a symmetry condition on that wall ? I assume your flow is "vertical, along y, or have I missed a point. In anycase take a look at the equations COMSOL uses for a symmetry plane that should inspire you to write your own weak constraint -- Good luck Ivar
Rui Silva
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Posted: 1 decade ago Jan 25, 2012, 3:30 p.m. EST
Hello Ivar,

thank you for your reply.

I cannot apply a symmetry in my geometry because the flow is horizontal and thus, gravity plays an important part.

In the same way that you use a weak constraint, let's say at the wall, like K=0, I would like to enforce something similar
in symmetry or middle of the flow, at max velocity point if you will. For instance: at the center of the pipe K=8.

And I am unsure how to do that...perhaps using the Wall Distance Interface...I will also look ate the equations as you suggested.

Best Regards,

Rui
Hello Ivar, thank you for your reply. I cannot apply a symmetry in my geometry because the flow is horizontal and thus, gravity plays an important part. In the same way that you use a weak constraint, let's say at the wall, like K=0, I would like to enforce something similar in symmetry or middle of the flow, at max velocity point if you will. For instance: at the center of the pipe K=8. And I am unsure how to do that...perhaps using the Wall Distance Interface...I will also look ate the equations as you suggested. Best Regards, Rui
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 25, 2012, 4:09 p.m. EST
Hi
indeed gravity can easily destroy symmetry in CFD, then you need to check if you cannot still separate your simulation into two and add them up later (delicate but sometimes possible)

If you can make a boundary at your mid stream line, then you can apply any equation on this boundary with some physics equation writing. Comsol always solves for "=0" so if you want to set a variable to a given constant you need to write (MyVariable - MyConstant) =0 plus any appropriate weak equations

--
Good luck
Ivar
Hi indeed gravity can easily destroy symmetry in CFD, then you need to check if you cannot still separate your simulation into two and add them up later (delicate but sometimes possible) If you can make a boundary at your mid stream line, then you can apply any equation on this boundary with some physics equation writing. Comsol always solves for "=0" so if you want to set a variable to a given constant you need to write (MyVariable - MyConstant) =0 plus any appropriate weak equations -- Good luck Ivar

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