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[ICEM] T Junction Meshing using ICEM CFD

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Old   November 11, 2012, 03:22
Default T Junction Meshing using ICEM CFD
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Karthick Selvam
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Hello,
I am new to ANSYS and I am currently learning meshing in ICEM CFD for my work on T Junction based flows. I have a few questions

1. What is the purpose of an O Grid? Is it only used at the boundaries? where can I learn more about the application of an O Grid?

2. The quality of mesh in the T Junction (where the two pipes intersect) where the important physics needs to be captured is average (It's related to my lack of understanding and using the blocking function properly). I have also posted some pictures which display the mesh along with the quality histogram. Any suggestion on how to improve the meshing functionality and reducing errors would be welcome. Thanks in advance.
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File Type: jpg pic1.jpg (15.4 KB, 97 views)
File Type: jpg pic2.jpg (95.2 KB, 93 views)
File Type: jpg Pic3.jpg (86.4 KB, 91 views)

Last edited by selvam2487; November 11, 2012 at 03:24. Reason: To remove some pictures
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Old   November 11, 2012, 05:11
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Download from this link

https://dl.dropbox.com/u/68746918/pipejunction_3d.zip
Attached Images
File Type: jpg a.jpg (54.2 KB, 141 views)
File Type: gif b.gif (38.1 KB, 133 views)
File Type: gif c.gif (29.2 KB, 109 views)
File Type: gif d.gif (41.5 KB, 114 views)
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Old   November 11, 2012, 06:33
Default thank you
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Hello Mr. Far,

Thank you very much for your help. I think I understand the blocking strategy that you have implemented. I will try to do it and see what happens.

Regards,
Karthick
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Old   November 11, 2012, 06:43
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Just brief steps :


1. Create main block
2. split at the junction and then two splits on the two sides of small pipe and perpendicular to bigger pipe
3. delete two blocks on right and left of the small pipe
4. Make associations
5. snap vertices.
6. make o-grid inside the small small upto the large pipe's bottom. Select two extreme faces.
7. Make the O-grid for the larger pipe and again select the respective end faces.
8. go to edge mesh parameters and update all sizes and go to second tab and give size 2 and apply. Keep on applying until mesh size is at-least 20000 hexas
9.Check premesh.
10. One horizontal split in the large pipe.
11. Play with vertices location panel to adjust the blocking to higher quality.
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Old   November 11, 2012, 14:35
Default Smooth mesh
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Smooth mesh after applying the elliptical solver.
Attached Images
File Type: jpg pipejunction_3d001.jpg (48.6 KB, 105 views)
File Type: jpg pipejunction_3d002.jpg (51.4 KB, 98 views)
File Type: jpg pipejunction_3d003.jpg (47.8 KB, 91 views)
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Old   November 12, 2012, 06:12
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Hello Mr. Far,

Could you please explain me as to what is the function of an O Grid? Also, when checking premesh quality histogram, the angles are not good? How to improve the angles in the mesh? Also, for this T junction geometry, what are the other Premesh quality criterion that should be checked?

Regards
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Old   November 12, 2012, 06:28
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Min angle is 32 and min quality is 0.6. which is good enough.
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Old   November 12, 2012, 12:21
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The O-Grid is very powerful because with this circular shape, O-Grid helps to have orthogonal cells around the circular shape.
Try to mesh a tube with, and without O-Grid, and it will be obvious
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Old   November 12, 2012, 12:32
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Mesh quality is 0.6 in ICEM and min orthogonal quality is 0.5 in Fluent and after smoothing (orthogonality) min mesh quality is 0.28 in ICEM and min orthogonal quality is 0.6 in Fluent.

Why smoothness decreases quality in ICEM and enhances the quality in Fluent?

What is the relationship between ICEM quality and Fluent orthogonal quality?
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Old   November 12, 2012, 13:00
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ICEM help manual about the quality :
Hexa

The quality is a weighted diagnostic between Determinant (between -1 and 1), Max Orthogls (normalized between -1 and 1; if deviation from orthogonality is greater than 90 degrees, then the normalized value will be smaller than 0) and Max Warpgls (normalized between 0 and 1; warpage of 0 degrees is 1, warpage of 180 degrees is 0). The minimum of the 3 normalized diagnostics will be used.

When you do orthogonal smoothing, you increase the orthogonal quality, but maybe, it also decreases the quality of your determinant.

I guess Simon could help us on that.
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Old   November 12, 2012, 13:06
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Check this Figure.

http://afinemesh.files.wordpress.com...el-529x359.png

Can you tell me which quality he is talking about?
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Old   November 26, 2012, 08:16
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Another idea.
1. Split selected block.
2. Split selected block.
3. Delete default associations of six edges and associate them to surface.
4. Snap Project Vertices.
Attached Images
File Type: jpg screen.jpg (46.3 KB, 108 views)
File Type: jpg screen1.jpg (43.4 KB, 100 views)
File Type: jpg screen2.jpg (73.9 KB, 99 views)
File Type: jpg screen3.jpg (29.7 KB, 93 views)
File Type: jpg screen4.jpg (74.9 KB, 93 views)
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Old   November 26, 2012, 08:18
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5. Create O-Grid with all blocks and faces of three ends.
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File Type: jpg screen5.JPG (85.1 KB, 116 views)
File Type: jpg screen61.jpg (97.2 KB, 117 views)
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Old   November 26, 2012, 10:03
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can you share the files?

By the way excellent comeback.
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Old   November 26, 2012, 10:49
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Ralen method is simple and somehow giving better quality and good looking mesh with few splits as you can see in attached pics(Mine in this post and Ralen' idea in next post.

My method:
Attached Images
File Type: jpg pipejunction_3d_Far001.jpg (70.7 KB, 69 views)
File Type: jpg pipejunction_3d_Far002.jpg (94.3 KB, 88 views)
File Type: jpg pipejunction_3d_Far003.jpg (95.4 KB, 91 views)
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Old   November 26, 2012, 10:51
Default Ralen's Method
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Here are the images from Ralen's Method:
Attached Images
File Type: jpg pipejunction_3d_Relenidea001.jpg (92.8 KB, 55 views)
File Type: jpg pipejunction_3d_Relenidea002.jpg (68.8 KB, 67 views)
File Type: jpg pipejunction_3d_Relenidea003.jpg (64.8 KB, 75 views)
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Old   November 27, 2012, 01:17
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http://www.sendspace.com/file/p70hlf
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Old   February 24, 2013, 22:09
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Hi Ralen,
The link is died, could you please upload again? Thank you very much!
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