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

[ANSYS Meshing] Streamlined vehicle boundary layer problem

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 3, 2014, 14:59
Default Streamlined vehicle boundary layer problem
  #1
New Member
 
Paul Mannion
Join Date: Nov 2014
Posts: 4
Rep Power: 2
Paul Fionn is on a distinguished road
Hi guys,

I've experienced problem while trying to create a mesh that captures the boundary layer effect on a streamlined vehicle shape.
The vehicle is shaped like a simple teardrop with a flat bottom. Only half the vehicle is modelled using symmetry.

The problem that occurs is that the front half of the vehicle meshes correctly however as the mesh progresses to the rear of the vehicle, it stops meshing the boundary layer in the same manner and essentially thins out replacing the desired mesh with large tet elements... (An image of the mesh is attached, I created a section cut through the middle to show how the mesh wraps around the shape at the front of the vehicle, it does not do this at the rear of the vehicle however)
I've also tried meshing the complete vehicle body shape without using symmetry but this did not yield any results.


Any help or advice would be greatly appreciated. I've tried every method of meshing with inflation within Ansys Meshing to find a solution but each yields the same result as above.
Regards
P
Attached Images
File Type: jpg mesh1.jpg (52.3 KB, 23 views)
Paul Fionn is offline   Reply With Quote

Old   November 4, 2014, 03:52
Default
  #2
Senior Member
 
Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
Posts: 185
Rep Power: 14
jrunsten will become famous soon enough
Send a message via MSN to jrunsten
Are you sure that all the surfaces on the car has inflation on them? Looks like they are deminishing to zero layers because the rear is not inflated (?) at all.
jrunsten is offline   Reply With Quote

Old   November 4, 2014, 12:52
Default
  #3
New Member
 
Paul Mannion
Join Date: Nov 2014
Posts: 4
Rep Power: 2
Paul Fionn is on a distinguished road
Hi jrunsten

I have inflation selected on all surfaces of the vehicle body, It breaks down into 3 surface components. The bottom, the side, and there is a minuscule area at the rear edge. I've tried knitting all these surfaces into one surface and applying inflation, and applying inflation to each of these surfaces seperatly. I've also tried eliminating the rear surface so that the only 2 surfaces were the bottom and the side. None of these yielded a different result.

If I examine the rear of the vehicle in close detail I find that the program is wrapping the rear of the shape 1 or 2 elements thick, if i select a high number of layers in the inflation menu (+40) then this layer reduces to 1 element thick at the rear, if i select a low number of layers (eg:5)in the inflation menu then the layer at the rear of the vehicle can increase to 3 elements thick

I attached 2 images to try and illustrate what is happening at the rear region of the vehicle
I apologise if my explanation above is not extremely helpful or intuitive
Attached Images
File Type: jpg MESH REAR END.jpg (18.1 KB, 4 views)
File Type: jpg MESH REAR END higly zoomed in.jpg (71.8 KB, 8 views)
Paul Fionn is offline   Reply With Quote

Old   November 4, 2014, 13:06
Default
  #4
Senior Member
 
Josef Runsten
Join Date: Jul 2010
Location: Gothenburg, Sweden
Posts: 185
Rep Power: 14
jrunsten will become famous soon enough
Send a message via MSN to jrunsten
Under the "Details" of "Mesh", enable "View advanced options" under "Inflation" and try switching collision avoidance from stairstepping to compression instead. That might work in your case.
jrunsten is offline   Reply With Quote

Old   November 4, 2014, 14:47
Default
  #5
New Member
 
Paul Mannion
Join Date: Nov 2014
Posts: 4
Rep Power: 2
Paul Fionn is on a distinguished road
Thanks for the advice, I gave it a go and here are the results
Unfortunately there was not much difference in the results between 'stair stepping' and 'layer compression. An image of the result of each is attached below

However I am glad to say that just from experimenting with other options under the same tab I managed to get a far more acceptable mesh made. The change i made was under 'Inflation growth rate type - maximum angle.'' I changed the angle from 90 deg to 180 deg, images are attached below.

This new mesh isn't perfect however as highlighted by the last image zoomed up at the rear end of the vehicle shape.

Also I noticed the following error appearing under all mesh generations.

''Pre-inflation layer generation is stopped because of face side limitation, proximity collisions and quality''
Attached Images
File Type: jpg maximum angle = 180 deg.jpg (77.3 KB, 8 views)
File Type: jpg layer compression.jpg (73.4 KB, 8 views)
File Type: jpg stairstepping.jpg (71.9 KB, 7 views)
File Type: png maximum angle = 180 deg zoomed.png (69.8 KB, 6 views)
Paul Fionn is offline   Reply With Quote

Old   November 4, 2014, 15:18
Default
  #6
New Member
 
Paul Mannion
Join Date: Nov 2014
Posts: 4
Rep Power: 2
Paul Fionn is on a distinguished road
I've managed to make further improvements by changing the 'maximum height over base' to its lowest value of 0.1

I attached 2 images below, one with 'stair stepping' collision avoidance and one with 'none' selected under collision avoidance, I was hoping you could shed some light on these commands? as I do not have a complete understanding on their effect on the mesh. Both mesh images attached below are similar however one does not have collision avoidance and the other does, so I am unsure as to which one is preferred.
Attached Images
File Type: jpg complete mesh (stair stepping).jpg (73.0 KB, 15 views)
File Type: jpg complete mesh (no collisian avoidance).jpg (60.2 KB, 16 views)
Paul Fionn 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
[GAMBIT] Problem with boundary layer - high skewness Muffins ANSYS Meshing & Geometry 4 February 28, 2014 08:34
Low Mixing time Problem Mavier CFX 5 April 29, 2013 00:00
Questions about Boundary Layer Thickness and Turbulence Models famerfamer STAR-CCM+ 3 July 12, 2012 09:47
High aspect ratio mesh problem for flat plate boundary layer sam1364 OpenFOAM 2 May 14, 2012 15:54
errors Fahad Main CFD Forum 0 March 23, 2004 14:20


All times are GMT -4. The time now is 22:51.