CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > ANSYS Meshing & Geometry

[ICEM] Meshing sharp edge (no airfoil)

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 16, 2012, 08:37
Default Meshing sharp edge (no airfoil)
  #1
Senior Member
 
Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
Posts: 185
Rep Power: 13
jrunsten will become famous soon enough
Send a message via MSN to jrunsten
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
File Type: jpg 2012-04-16 14-27-17.jpg (10.6 KB, 193 views)
jrunsten is offline   Reply With Quote

Old   April 17, 2012, 05:53
Default
  #2
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
Divide into two blocks with vertical split and then merge vertices on sharp side and then use Y-blocking.
Far is offline   Reply With Quote

Old   April 17, 2012, 08:04
Default
  #3
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
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.
Far is offline   Reply With Quote

Old   April 17, 2012, 08:17
Default
  #4
Senior Member
 
Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
Posts: 185
Rep Power: 13
jrunsten will become famous soon enough
Send a message via MSN to jrunsten
Quote:
Originally Posted by Far View Post
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.
Attached Images
File Type: jpg 2012-04-17 14-11-56.jpg (14.9 KB, 137 views)
jrunsten is offline   Reply With Quote

Old   April 17, 2012, 08:56
Default
  #5
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
If your geometry has a tight angle, you should assume that your mesh, which is fit to your geometry, will also have a sharp angle. It will even be sharper than that if you want multiple elements across the gap.

If I were to capture this geometry as it is, I would use wedge blocks in those corners.

Another option is to not do that exact geometry shape. Many analysts would argue that the flow thru to the very tip of that cusp is very slight and that leaving it off would not change your results very much... You could trim off the cusp somewhere near the tip. this would change your topology to something with a square end...

But Far just assumed you were asking about Hexa mesh... Is that your goal or are you looking for tetra solutions?
__________________
-----------------------------------------
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
PSYMN is offline   Reply With Quote

Old   April 17, 2012, 08:59
Default
  #6
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
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.
Far is offline   Reply With Quote

Old   April 17, 2012, 09:05
Default
  #7
Senior Member
 
Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
Posts: 185
Rep Power: 13
jrunsten will become famous soon enough
Send a message via MSN to jrunsten
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
jrunsten is offline   Reply With Quote

Old   April 17, 2012, 12:36
Default
  #8
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
Quote:
Originally Posted by Far View Post
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.
__________________
-----------------------------------------
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
PSYMN is offline   Reply With Quote

Old   April 18, 2012, 04:06
Default Paradox - Quality and Angle
  #9
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
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?
Far is offline   Reply With Quote

Old   April 18, 2012, 21:42
Default
  #10
Senior Member
 
PSYMN's Avatar
 
Simon Pereira
Join Date: Mar 2009
Location: Ann Arbor, MI
Posts: 2,662
Blog Entries: 1
Rep Power: 35
PSYMN has a spectacular aura aboutPSYMN has a spectacular aura about
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
PSYMN is offline   Reply With Quote

Old   April 21, 2012, 02:14
Default NACA66012 mesh problem
  #11
New Member
 
SANTOSH
Join Date: Jan 2012
Posts: 10
Rep Power: 5
dnsantosh is on a distinguished road
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
dnsantosh is offline   Reply With Quote

Old   April 24, 2012, 03:06
Default is it possible..?
  #12
New Member
 
SANTOSH
Join Date: Jan 2012
Posts: 10
Rep Power: 5
dnsantosh is on a distinguished road
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
dnsantosh is offline   Reply With Quote

Old   April 24, 2012, 04:21
Default shall meshing and then prism
  #13
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
This is the bottom up approach. First make the shell meshing and then set the parameters for prism and compute mesh. you are done.
Far is offline   Reply With Quote

Old   April 24, 2012, 04:35
Default generating pyramids with prisms
  #14
New Member
 
SANTOSH
Join Date: Jan 2012
Posts: 10
Rep Power: 5
dnsantosh is on a distinguished road
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
dnsantosh is offline   Reply With Quote

Old   April 24, 2012, 04:49
Default
  #15
Far
Super Moderator
 
Far's Avatar
 
Sijal Ahmed Memon (turboenginner@gmail.com)
Join Date: Mar 2009
Location: Islamabad Pakistan
Posts: 3,905
Blog Entries: 6
Rep Power: 38
Far will become famous soon enoughFar will become famous soon enough
Send a message via Skype™ to Far
set prism quality to 0.00001 to avoid pyramids.
Far is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
how to set periodic boundary conditions Ganesh FLUENT 13 January 22, 2014 05:11
Meshing of a sharp edge orifice with a radius Moose1231 STAR-CD 3 December 6, 2011 16:32
Gambit - meshing over airfoil wrapping (?) problem JFDC FLUENT 1 July 11, 2011 05:59
fluent add additional zones for the mesh file SSL FLUENT 2 January 26, 2008 12:55
meshing a sharp edge line CFX 2 November 2, 2002 12:19


All times are GMT -4. The time now is 04:39.