CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

High aspect ratio

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 8, 2014, 18:52
Default High aspect ratio
  #1
New Member
 
Jack Holmes
Join Date: Feb 2014
Posts: 9
Rep Power: 3
jackholmes is on a distinguished road
Hi all,

I am trying to create a dynamic mesh but keep getting the error

WARNING: The mesh contains high aspect ratio quadrilateral,
hexahedral, or polyhedral cells.
The default algorithm used to compute the wall
distance required by the turbulence models might
produce wrong results in these cells.
Please inspect the wall distance by displaying the
contours of the 'Cell Wall Distance' at the
boundaries. If you observe any irregularities we
recommend the use of an alternative algorithm to
correct the wall distance.
Please select /solve/initialize/repair-wall-distance
using the text user interface to switch to the
alternative algorithm

How do I fix this as when I preview my dynamic mesh I get a negative volume.

Any help and advice would be great.

Thanks all,

Jack
jackholmes is offline   Reply With Quote

Old   March 9, 2014, 16:14
Default
  #2
New Member
 
Mack
Join Date: Aug 2013
Location: UK
Posts: 16
Rep Power: 3
Mack is on a distinguished road
Hi Jack,

Are you using a structured or unstructured mesh? Are you using a low Reynolds approach? If yes, do not worry about this message, even though you can correct this repairing the wall distance via TUI (as stated in the error message).
However, if you are using an unstructured mesh and a high Reynolds approach then you may have bad quality elements (very skewed ones). You must check your mesh when uploading it on Fluent. You can also smooth it, if this is the case.
As your geometry is very simple I would recommend you to use a block structured mesh with an o-grid.

Regards,
Mack
Mack is offline   Reply With Quote

Old   March 10, 2014, 06:26
Default Email
  #3
New Member
 
Jack Holmes
Join Date: Feb 2014
Posts: 9
Rep Power: 3
jackholmes is on a distinguished road
Can i ask for your email and send you the mesh to see if theres anything you can do.

If not, no worries and thank you anyway

Jack
jackholmes is offline   Reply With Quote

Old   March 10, 2014, 16:00
Default
  #4
New Member
 
Mack
Join Date: Aug 2013
Location: UK
Posts: 16
Rep Power: 3
Mack is on a distinguished road
Hi Jack,

Sorry but I do not have Fluent/ICEM anymore. Did you take a look on the 2D cylinder mesh tutorial?
Mack is offline   Reply With Quote

Old   March 12, 2014, 22:31
Default
  #5
New Member
 
ganhai
Join Date: Feb 2014
Posts: 14
Rep Power: 3
france is on a distinguished road
Hi,Mack
I also get into the same trouble with Jack.My model with unstructured mesh and big Reynolds approach.
How can I improve my mesh quality .
france is offline   Reply With Quote

Old   March 13, 2014, 18:40
Default
  #6
New Member
 
Mack
Join Date: Aug 2013
Location: UK
Posts: 16
Rep Power: 3
Mack is on a distinguished road
Hi Ganhai,

Have you tried to smooth the mesh? You can do it either on your meshing program or on fluent. If you check the mesh on fluent prior to the movement and everything is ok, then it means that your moving parameters are not ok. Do not forget to apply movement to the cylinder volume and not just to the walls. Take a look on the tutorial I mentioned before, it may help.

Regards,
Mack
Mack is offline   Reply With Quote

Old   March 13, 2014, 21:14
Default
  #7
New Member
 
ganhai
Join Date: Feb 2014
Posts: 14
Rep Power: 3
france is on a distinguished road
Hi Mark,Thank you for your reply!Here i give my icem model for you.I really appreciate you can take some time have a look.
Thanks again.
france
Attached Images
File Type: jpg 360??20140314083000309.jpg (86.8 KB, 25 views)
File Type: jpg 360??20140314083037165.jpg (89.7 KB, 17 views)
Attached Files
File Type: zip ICEMCFD-france.zip (84.5 KB, 6 views)
france is offline   Reply With Quote

Old   March 14, 2014, 10:06
Default
  #8
New Member
 
Mack
Join Date: Aug 2013
Location: UK
Posts: 16
Rep Power: 3
Mack is on a distinguished road
Hi Ganhai,

Is that a hollow cylinder? Is it 2D or 3D?
Sorry, but I could not understand your geometry with these pictures.
It seems that you have very stretched elements, so you should try to square them increasing the number of cells on the edges.
Mack is offline   Reply With Quote

Old   March 14, 2014, 20:48
Default
  #9
New Member
 
ganhai
Join Date: Feb 2014
Posts: 14
Rep Power: 3
france is on a distinguished road
Hi,Mack
It is 3D and the surface of the up and down are sphere.If I increasing the number of cells on the edges the whole model will have several millions elements.Then my compute nearlly can't deal with it.So,Is there any way I can solve this problem.
france is offline   Reply With Quote

Old   March 15, 2014, 11:08
Default
  #10
New Member
 
Mack
Join Date: Aug 2013
Location: UK
Posts: 16
Rep Power: 3
Mack is on a distinguished road
Hi Ganhai,

Well, as your geometry is quite symmetric you can take advantage of this and simulate just a fraction of the domain.
Try to simulate just a "piece of cake", applying symmetry condition to both sides. It will save you enormous computational effort.
Mack is offline   Reply With Quote

Old   March 16, 2014, 21:18
Default
  #11
New Member
 
ganhai
Join Date: Feb 2014
Posts: 14
Rep Power: 3
france is on a distinguished road
ok,Mack. I will try it.No matter how,I will let you konw the result.Thanks again.
france is offline   Reply With Quote

Reply

Tags
dynamic mesh, fluent, high aspect ratio, negative volume error

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
MUSCL shock capturing on high aspect ratio meshes vijay_paul Main CFD Forum 1 September 29, 2012 00:16
High aspect ratio oort OpenFOAM 5 September 16, 2011 14:06
High Aspect Ratio elements Flavio CFX 2 November 24, 2006 13:01
Multicomponent fluid Andrea CFX 2 October 11, 2004 05:12
Aspect Ratio at high turbulent and swirled flows zago FLUENT 0 May 19, 2004 02:37


All times are GMT -4. The time now is 09:27.