# [ICEM] Meshing sharp edge (no airfoil)

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April 16, 2012, 08:37
Meshing sharp edge (no airfoil)
#1
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Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
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Hi,

I am looking for some advice regarding meshing of really sharp geometry. Lets concider a geometry like the one in the image below. Is there a way to produce a nice quality mesh in sharp points like these? Which ever way I think about it it always ends up with crappy mesh in that area, and there's no point in starting the meshing before I have a clear idea of how to do it. Any advise?
Attached Images
 2012-04-16 14-27-17.jpg (10.6 KB, 195 views)

 April 17, 2012, 05:53 #2 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,915 Blog Entries: 6 Rep Power: 38 Divide into two blocks with vertical split and then merge vertices on sharp side and then use Y-blocking.

April 17, 2012, 08:04
#3
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Quote:
 I am looking for some advice regarding meshing of really sharp geometry
The real question is not how to mesh the really sharp corner, but the question is how to get the angle greater than 18 in such sharp corners.

April 17, 2012, 08:17
#4
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Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
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Quote:
 Originally Posted by Far The real question is not how to mesh the really sharp corner, but the question is how to get the angle greater than 18 in such sharp corners.
Thanks. Well yes, those two questions do come hand in hand I would say, and your formulation of the problem is really what I am interested in. I'm guessing some kind of modification to the geometry is needed.

The entire model consists of a tube splitting into two smaller ones (left out if the image), similar to the attached image. So its not as simple as I hinted in the first post. As you can see there are two such sharp corners.
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 2012-04-17 14-11-56.jpg (14.9 KB, 139 views)

April 17, 2012, 08:59
#6
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Quote:
 If I were to capture this geometry as it is, I would use wedge blocks in those corners.

Will Wedge block be more efficient than Y-block for the Fluent and CFX?

I just want to confirm that wedge block is formed when block is collapsed at one edge or we need to go to transform block >>>>> wedge block.

 April 17, 2012, 09:05 #7 Senior Member   Josef Runsten Join Date: Jul 2010 Location: Gothenburg, Sweden Posts: 185 Rep Power: 14 Thanks Simon! Yes I am looking for all hex. The pipes are very long so to save on elements in the streamwise direction I would like to avoid tetras. Slicing the domain in complicated areas like this and mesh with tetra and then sweep the pipes, is what I was thinking at first (in Workbench). But I was curious about doing it all in hexa

April 17, 2012, 12:36
#8
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Simon Pereira
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Quote:
 Originally Posted by Far Will Wedge block be more efficient than Y-block for the Fluent and CFX? I just want to confirm that wedge block is formed when block is collapsed at one edge or we need to go to transform block >>>>> wedge block.
Yes, when you have a tight angle like that, a wedge fits more naturally than trying to squish a hex element (even as part of a Ygrid) into that same space.

And yes, you can get a wedge block just by collapsing one face of a block... Hexa is smart enough to convert collapsed end elements to Penta-6 instead of collapsed hexas when you output to unstructured mesh.
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 April 18, 2012, 04:06 Paradox - Quality and Angle #9 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,915 Blog Entries: 6 Rep Power: 38 Right now I am also working on geometry which has the real sharp corner(water turbine to be precise). Initially I was working with Y-block in the sharp corner and quality comes out to be > 0.4. When checked in CFX (reconfirmed in ICEM as well) I got the warning about the minimum angle with value of 10.3 deg. So after the yesterday's discussion I have converted that block into wedge block and now minimum angle comes out to be > 23 but the quality is 0.1 for the cells in that corner. Rest of the mesh has quality greater than 0.4. Now I have no solution for this situation. Any suggestion?

 April 18, 2012, 21:42 #10 Senior Member     Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,662 Blog Entries: 1 Rep Power: 35 Yea, just don't worry about it... The problem is that the quality metric for prisms (penta-6) is really harsh. It takes the element and divides it into 3 tetras and then computes the quality of each and reports the worst. As a result of the totally different computation, you can't really compare prism quality with other elements. I have pushed several times to have this metric changed to not appear so negative for our prisms, but some older customers have setup all sorts of scripts based on this current formulation and don't want us to change anything there... Try it in your solver, it won't mind those prisms a bit. __________________ ----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey

 April 21, 2012, 02:14 NACA66012 mesh problem #11 New Member   SANTOSH Join Date: Jan 2012 Posts: 10 Rep Power: 5 hi am trying to do tri mesh on naca66012 symmetry airfoil wing surface, because of its sharp trailing edge its not capturing mesh correctly, if i make it blunt or give some radius by making sharp to curve,if make it is there any changes will occur in results.? thank you

 April 24, 2012, 03:06 is it possible..? #12 New Member   SANTOSH Join Date: Jan 2012 Posts: 10 Rep Power: 5 is it possible to generate only prism on UAV by using ICEMCFD and generate tera on other software and merge them ,,,,if possible how to generate ony prisms in ICEM thank you

 April 24, 2012, 04:21 shall meshing and then prism #13 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,915 Blog Entries: 6 Rep Power: 38 This is the bottom up approach. First make the shell meshing and then set the parameters for prism and compute mesh. you are done.

 April 24, 2012, 04:35 generating pyramids with prisms #14 New Member   SANTOSH Join Date: Jan 2012 Posts: 10 Rep Power: 5 thanks for replying far i tried that method but it generating pyramids with prisms i need only prisms ,how to avoid that , i need 30mm ( total prism height ) thank you

 April 24, 2012, 04:49 #15 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,915 Blog Entries: 6 Rep Power: 38 set prism quality to 0.00001 to avoid pyramids.

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