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Old   July 1, 2002, 10:58
Default shadow faces!
Andrew Flintoff
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I just finished meshing a geometry in GAMBIT and defined the boundary conditions also in GAMBIT, and exported it to FLUENT. Now, when I looked at the "DISPLAY GRID" menu, I got 3 SHADOW FACES. I have no clue what these are and why they are created. I would appreciate if anyone could explain this to me.


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Old   July 1, 2002, 11:37
Default Re: shadow faces!
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Hi Andy. I went throught the same problem a couple of days ago. In my case, the reason for the generation of shadow faces was that there was no thickness of the wall I had meshed. If this solid wall was in contact with more than one face, FLUENT will generate as many extra walls as needed for not to mesh the same wall twice. Note that this "imaginary walls" lie just on top of the ones you have in GAMBIT (or whatever mesh generator you are using). In other terms, FLUENT will generate shadow faces for those solid walls that are in contact with more than one meshed face. If you have something like this in your geometry you coul try and give the prongs a small thickness, and that message should disappear. Another thing you could try is to disconnect the mesh from both sides of the thicknessless bits. I don't know if I explained myself well or if your case is similar to this, but I hope this is of some help to you.
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Old   July 2, 2002, 04:02
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leave the shadows as they are. Dont't disconnect the mesh and don't create walls with thikness because you have shadows.

If there is fluid/solid on both sides of a wall face, Fluent creates a wall-shadow. One of the pair wall - wall-shadow communicates with one fluid-side, the other communicates with the second fluid-side. This is just the way Fluent handles these walls.

If you change the wall boundary condition for one of these two to interface, the shadow will dissapear.

The good thing about how Fluent handles double-sided walls is that you can specify different boundary-conditions (e.g. thermal conditions) on the two sides.

More info is to be found in the manual.


Laika, still orbiting
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Old   July 2, 2002, 16:11
Default Re: shadow faces!
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A face thread cannot belong to more than one cell thread in a Fluent 5/6 mesh. You don't need to modify your grid!

BTW, you can give the wall and it's shadow different boundary conditions. neat.
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