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Which one is a correct smallest geometry unit?

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Old   January 16, 2019, 11:47
Unhappy Which one is a correct smallest geometry unit?
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Zari Musavi
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Hi everyone,

I am preparing a 3D geometry to be modeled in Fluent later.

I am in doubt what could be the smallest unit that I can choose.

The physical system is a chamber having hundreds of small tubes as inlets from two ends, as it shown in the attachment "Geometry 3D".


The cross section at each end looks like the attached image "Geometry 2D".

As you can see it is very periodic or symmetric.


I considered the following two cross sections at inlet boundaries. The first is one inlet tube + part of 9 neighbors, shown as the attachment "unit 1".

and the second is one inlet + part of the 4 neighbor inlets, shown as the attachment "unit 2".

Q1: Which one do you think is correct or is enough?

Q2: Do you have other suggestions for the smallest geometry unit to model this system?


Q3: I have thought to set all side-boundaries as symmetric. Do you think a periodic boundary would be better?

Thank you in advance for your time and help.

Zari
Attached Images
File Type: png Geometry 3D.PNG (132.5 KB, 9 views)
File Type: png Geometry 2D.png (94.1 KB, 13 views)
File Type: png unit 1.png (13.6 KB, 10 views)
File Type: png unit 2.png (11.3 KB, 5 views)
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Old   January 16, 2019, 11:52
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Lucky Tran
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You can go even smaller like so. The trick is to recognize all the lines of symmetry and choose the nearest ones. Actually you can go even smaller than the square I have drawn by slicing along the diagonal and simulating a triangular shaped domain. However, I like to avoid these triangular/wedge shapes because meshing them becomes funky.


Periodic or symmetry should work. Symmetry is a stronger constraint and would be preferred. Symmetry is also easier since you don't need a conformal mesh.
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File Type: png unit 1.png (13.9 KB, 10 views)
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Old   January 16, 2019, 13:48
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Zari Musavi
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Thanks LuckyTran,


If I choose the smaller unit, similar to you draw, the effects from the other inlets might be neglected. All circular shapes are inlets and the space between them is walls.
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Old   January 16, 2019, 13:53
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Oh I didn't realize it was counterflow. It's hard to understand you. Then maybe something like so.
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