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Beginner question :(. Turning on and off zones?

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Old   September 1, 2009, 09:58
Default Beginner question :(. Turning on and off zones?
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Chris Laumans
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Hello,

I'm a cfd beginner and am having trouble with something that I think should be pretty simple, but am unable to get it working. So hopefully someone could quickly help me out.
I'm modelling heat transfer into a cooking pan, and I have lots of different geometries that I would like to compare.
Instead of making a new mesh for each geometry, how do I need to go about using only 1 msh file?
i.e. I have a 2d area which I'm considering, inside of that mesh I want to place a wall of 0.5mm thick that I can turn on and off in fluent to compare the effect of the wall.
How do I need to go about defining the zones in gambit so that I can activate and deactivate the areas in fluent?
In fluent I found the activate/deactivate function, but I haven't gotten it to work, since I seem to only be able to turn off the mesh INSIDE of the wall, but the wall itself stays there..
Thanks a bunch, I hope this is clear.

Chris
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Old   September 1, 2009, 12:26
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Is the wall connected to other types of boundaries (e.g. symmetric BC)? If so, try change those BCs to Wall type BC and do activate/deactivate again.

Regards,
John
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Old   September 1, 2009, 13:00
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Chris Laumans
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Hi John,

Thank you for your reply. The wall is not connected to other boundaries.

Basically I have 2 faces, 1 inside of the other. It is the inside face that I would like to turn on and off.
What I was previously doing was creating 2 faces, and then using the subtract button in Gambit to end up with 1 face and the fluid volume that I needed. However now I think I need to retain the two faces but I'm not sure how I should set up the zones or the meshes.
I hope I'm explaining myself clearly, please tell me if things are still unclear.

Thanks
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Old   September 1, 2009, 13:37
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Chris Laumans
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I've made a simple sketch of what I would like to do. (attachment)
Somewhere I have a velocity inlet, elsewhere a pressure outlet. Within the fluid volume I have an obstacle, and I would like to be able to turn it on and off.
Previously I was making separate files for each case, one with and one without the object. But from what I understand there should be an easier way. My questions are how should i set the geometry up in gambit to be able to turn on and off the obstacle in fluent?
I've been experimenting with this simple case, but can't figure out how I should set it up.

1. Should I keep the two boxes as separate faces?
2. Do I need to have 2 meshes, 1 inside the inner box, 1 inside the outer box? Or does turning off the inner box in fluent correct the mesh automatically?
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File Type: jpg box.jpg (17.7 KB, 17 views)
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Old   September 1, 2009, 20:23
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Chris
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Quote:
Originally Posted by Cjlaumans View Post
I've made a simple sketch of what I would like to do. (attachment)
Somewhere I have a velocity inlet, elsewhere a pressure outlet. Within the fluid volume I have an obstacle, and I would like to be able to turn it on and off.
Previously I was making separate files for each case, one with and one without the object. But from what I understand there should be an easier way. My questions are how should i set the geometry up in gambit to be able to turn on and off the obstacle in fluent?
I've been experimenting with this simple case, but can't figure out how I should set it up.

1. Should I keep the two boxes as separate faces?
2. Do I need to have 2 meshes, 1 inside the inner box, 1 inside the outer box? Or does turning off the inner box in fluent correct the mesh automatically?
I've attached a picture to show you what I would do. In Gambit, mesh the outer fluid region as one zone, the soild (i.e., wall thickness) as one zone, and the inner fluid as one zone. Then, define the faces that comprise the walls of the solid as "wall", and assign a continuum type of "fluid" to the inner and outer fluid zones, and "solid" for the region contained between the walls.

In FLUENT, to "remove" the inner obstacle, change the "solid" zone to "fluid", and then change the "wall" boundary conditions to "interior" under Define-->Boundary Conditions.

When you change the "solid" zone to "fluid", FLUENT might give you an error due to the fact that that you have a zero-thickness wall between two fluid zones. To solve this problem, FLUENT creates a shadow region, which is bascially two zero thickness walls stacked on top of each other, which enables a 1D conduction problem to be solved to calculate heat transfer through the wall. If this happens, go to Grid-->Fuse Faces (or something like that, I don't have it in front of me) and merge the "stacked" faces together, which will combine both faces into one "interior" face.
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Old   September 1, 2009, 20:35
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Hi Chris,

What you're trying to do should be fairly simple.
In Gambit:
1) Create the two faces.
2) Split (don't subtract) the larger face with the smaller one (connected).
3) Mesh both faces
4) Assign BCs, with the walls of the inner face as interiors, not walls.
5) Specifiy continuum names for each face (i.e. inner and outer).
In Fluent:
1) Perform the calculations for the whole plate.
2) When you are ready to explore the other design, deactivate the inner face (Grid-->zone-->deactivate).
When you deactivate this zone, the boundaries automatically become walls.

I hope this helps

Regards
AAA
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Old   September 2, 2009, 15:44
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Chris Laumans
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Thanks a lot!

I got everything working
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