# [ICEM] 2d hemisphere in wind tunnel

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 June 6, 2012, 11:48 #21 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 I am not happy with mesh. I dont know why mesh goes circular to square shape and then again square to circular. In this type of geometry where internal and external parts have similar shape, we should have the very good looking circular mesh. Any idea why this is happing?

June 7, 2012, 02:37
#22
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reza
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Quote:
 Originally Posted by Far Follow shpere-cube tutorial. What do you mean by good quality?
I Followed it but the main problem is the bottom circle of the hemisphere. It itself need a 2D O-grid but in 3D blocking it is not possible as I know.
here is a 2D o-grid for a circle.
Attached Images
 o-grid.png (60.4 KB, 94 views)

Last edited by reza45000; June 7, 2012 at 04:23.

June 7, 2012, 04:07
#23
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reza
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Quote:
 Originally Posted by Far were you looking for this. Just deleted lower part of sphere!!! do you need it? I am not sure.
it is impossible because Left Far-field and Right Far-field are Inlet and Outlet or vice versa.

Quote:
 Originally Posted by Far try this.......strategy is similar to sphere-cube tutorial
as you mentioned it is not a good one, look at the min angle: we have 0-9 degree cells.
Attached Images
 min angle.jpg (48.1 KB, 93 views)

 June 7, 2012, 04:35 #24 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 No, It is not true. You must have activated solid part. I was talking about the general mesh shape otherwise quality is good and angle is higher than 40. I guess we are on different track. I guess circle should be hollow. Can you describe your problem again with geometry pics to be modelled and some additional description?

June 7, 2012, 05:49
#25
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reza
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Quote:
 Originally Posted by Far No, It is not true. You must have activated solid part. I was talking about the general mesh shape otherwise quality is good and angle is higher than 40. I guess we are on different track. I guess circle should be hollow. Can you describe your problem again with geometry pics to be modelled and some additional description?
Here is a sample picture: the hemisphere is solid not hollow

and we need farfield as I created in the geometry file.
Attached Images
 hemisphere.png (36.1 KB, 91 views)

 June 7, 2012, 06:30 #26 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 Ok , got it. Nevertheless, we still make the hemishpere as hollow since fluid is not going inside. In this case the far feild on the other side should be rectangular in shape to ease the meshing.

 June 7, 2012, 06:45 #27 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 In the mean time for hemisphere section, use strategy we have just discussed. And in the other part with flat end (cylindrical enclosure), use simple topology and then create o-grid inside circular base all the way to end of cylindrical domain. Got it?

June 7, 2012, 07:41
#28
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reza
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Quote:
 Originally Posted by Far Ok , got it. Nevertheless, we still make the hemishpere as hollow since fluid is not going inside. In this case the far feild on the other side should be rectangular in shape to ease the meshing.
I think it has no difference. The block associates with the far field whether in sphere shape or rectangular.

Quote:
 Originally Posted by Far In the mean time for hemisphere section, use strategy we have just discussed. And in the other part with flat end (cylindrical enclosure), use simple topology and then create o-grid inside circular base all the way to end of cylindrical domain. Got it?
Sorry I didn't.
I think my problem is the mesh on the bottom of hemisphere (as I showed in previous comments) that we should make a 2d o-grid on that circle but I couldn't do it.
If you have time to make a correct blocking, I will appreciate.

 June 7, 2012, 07:43 #29 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 I have already started to work on this. Going to post it shortly reza45000 likes this.

June 8, 2012, 09:21
Done
#30
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Done. It has some tricky part, when I was trying to snap vertices to hemisphere. Unlike the space cube tutorial where all things were done nicely with associate vertex to point on the inner cube, but this is not the case with this problem.

Enjoy and let me know if you get same problem as discussed above.
Attached Files
 Hemisphere 3d_cylindericalout_Far.zip (16.3 KB, 16 views)

 June 8, 2012, 13:52 pics #31 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 Pics:

June 11, 2012, 04:40
#32
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reza
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Quote:
 Originally Posted by Far Done. It has some tricky part, when I was trying to snap vertices to hemisphere. Unlike the space cube tutorial where all things were done nicely with associate vertex to point on the inner cube, but this is not the case with this problem. Enjoy and let me know if you get same problem as discussed above.
Fantastic, I also did it and you can see. Thank you for your attention.You create a hemisphere part including the large circle. I create the hemisphere part exactly the hemisphere so in association process first I associate the bottom of block to bottom of hemisphere (using "associate edge to curve") and then associate the faces of my inner block to hemisphere part(using "associate face to surface") and finally using "snap Project vertices" vertices go to the right position and there is no need to move vertices manually.

Thanks again.
Attached Files
 Hemisphere 3.zip (20.6 KB, 10 views)

 June 11, 2012, 07:24 I learn to feel the ICEM #33 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 I guess, now I am feeling the ICEM from heart. For example in this case if you snap the outer block first and then inner block, you will get the mesh problems as I have stated previously. You have to snap vertices at once. So make all oblocks, change material and snap the vertices. Mine vertices for inner block were placed at Y= 1.9, while Reza's vertices (same vertices) were found to be at Y = 2.9. When used above trick or method, I have also got the vertices at Y = 2.9. Have fun.

June 11, 2012, 07:26
#34
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Quote:
 using "associate face to surface")
Dont use this method, this method is used for making the internal wall. You just need to change the material and you will get the mesh on hemisphere.

June 11, 2012, 08:46
#35
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reza
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Quote:
 Originally Posted by Far Dont use this method, this method is used for making the internal wall. You just need to change the material and you will get the mesh on hemisphere.
I didn't exactly understand Why not to use it?
How do you associate the inner block to hemisphere?

 June 11, 2012, 08:54 #36 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,900 Blog Entries: 6 Rep Power: 37 When you delete the internal block or change its material, icem automatically makes the associations.

July 8, 2012, 05:21
#37
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Quote:
 Originally Posted by Far I am not happy with mesh. I dont know why mesh goes circular to square shape and then again square to circular. In this type of geometry where internal and external parts have similar shape, we should have the very good looking circular mesh. Any idea why this is happing?

I found the reason for this. This is because I have forgot to switch back transfinite degree = Quadratic to transfinite degree = linear (linear is default option), so ICEM made it my default method and I was wondering for weeks that this is bug in ICEM. But now things are good .

Mid and outlet plane with quadratic option:

Mid and outlet plane with linear option

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