# [ANSYS Meshing] Meshing a very long and tiny duct

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 January 16, 2021, 06:01 Meshing a very long and tiny duct #1 New Member   simone Join Date: Nov 2019 Posts: 2 Rep Power: 0 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 (). To do this I tried to generate the grid with an Element Size of , 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 ). 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

 January 17, 2021, 15:39 #2 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,741 Rep Power: 25 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. aero_head likes this.

 January 19, 2021, 05:15 #3 Senior Member   Lorenzo Galieti Join Date: Mar 2018 Posts: 348 Rep Power: 11 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

January 20, 2021, 04:43
#4
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simone
Join Date: Nov 2019
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thank you very much for your responses.
Regarding the suggestion of Gert-Jan.
Quote:
 Originally Posted by Gert-Jan 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 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
 duct.jpg (41.0 KB, 9 views)

January 20, 2021, 12:05
#5
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Lorenzo Galieti
Join Date: Mar 2018
Posts: 348
Rep Power: 11
Quote:
 Originally Posted by simo88 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.

 January 21, 2021, 13:57 #6 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,140 Rep Power: 22 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.

 January 21, 2021, 17:24 #7 Senior Member   Lorenzo Galieti Join Date: Mar 2018 Posts: 348 Rep Power: 11 Just read his last post, he said it's 2D

 Tags duct flow, mesh 2d, meshing ; solver settings