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[ANSYS Meshing] Meshing a very long and tiny duct

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Old   January 16, 2021, 06:01
Default Meshing a very long and tiny duct
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simone
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Hi, I am new to Ansys suite and after doing some testing in similar cases, I ran into this problem:
On Meshing I have to mesh a very thin and very long duct (10^{-4} \times 1). To do this I tried to generate the grid with an Element Size of 5\cdot10^{-6}, but in this way the computer works for a long time at a high cost of resources without leading to anything (I estimate in fact that the number of cells is of the order of 4 \cdot 10^{6}). Reducing instead the Element Size I get a useless grid. The problem is in the huge difference in the order of magnitude of the two dimensions of the duct.
Do any of you have any idea how I could solve this problem?
I was thinking for example to divide the geometry into several parts, but then I do not know how to impose the conditions of "continuity", or to limit myself to study only the first half of the duct being symmetrical, but even in this case I do not know how to deal with any conditions to be imposed.

Thanks to those who can and will help me
Simone
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Old   January 17, 2021, 15:39
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Gert-Jan
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What might help is to create a mesh in a geometry that is less streched. I would reduce the size by a x,y,z factor of 0.1,1,1 or maybe even 0.01,1,1
Then after meshing, read it into Fluent, CFX, or what soever and scale it back by 10,1,1 or 100,1,1.
Indeed, alternatively mesh smaller parts. Then in Fluent or CFX, copy and multiply the geometry. In CFX, you have the option to glue the copied parts automatically to a single geometry.
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Old   January 19, 2021, 05:15
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Lorenzo Galieti
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Can you please post a screenshot of the geometry? I think you may use sweep method to get a nice mesh with low computational time
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Old   January 20, 2021, 04:43
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thank you very much for your responses.
Regarding the suggestion of Gert-Jan.
Quote:
Originally Posted by Gert-Jan View Post
What might help is to create a mesh in a geometry that is less streched. I would reduce the size by a x,y,z factor of 0.1,1,1 or maybe even 0.01,1,1
Then after meshing, read it into Fluent, CFX, or what soever and scale it back by 10,1,1 or 100,1,1.
Indeed, alternatively mesh smaller parts. Then in Fluent or CFX, copy and multiply the geometry. In CFX, you have the option to glue the copied parts automatically to a single geometry.
I tried, but the simulation does not go to convergence.
As requested by LoGaL
Quote:
Originally Posted by LoGaL View Post
Can you please post a screenshot of the geometry? I think you may use sweep method to get a nice mesh with low computational time
I post my geometry. it is a 2D duct whose top edge is a portion of sine function.
If it turns out well, can you give me some detailed guidance on how to apply that method?
Attached Images
File Type: jpg duct.jpg (41.0 KB, 10 views)
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Old   January 20, 2021, 12:05
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Lorenzo Galieti
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Quote:
Originally Posted by simo88 View Post
thank you very much for your responses.
Regarding the suggestion of Gert-Jan.

I tried, but the simulation does not go to convergence.
As requested by LoGaL

I post my geometry. it is a 2D duct whose top edge is a portion of sine function.
If it turns out well, can you give me some detailed guidance on how to apply that method?
If it is 2D the sweep method can't be used. What surprises me is that you can't mesh it at all. are you using quad dominant mesh method? If yes, quite normal that it takes time.
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Old   January 21, 2021, 13:57
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Sweep method should be perfect for this if this is 3D. I don't understand when you say it is 2D? Is your picture just the cross section? And then it is extended very long in the Z direction?
Just use sweep method, mapped faces, and edge sizing number of divisions for specifying your mesh. use the same number of divisions on parallel edges, including the bottom and the sine wave edges, they count as "parallel" in me description.
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Old   January 21, 2021, 17:24
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Just read his last post, he said it's 2D
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