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

Pressure far field boundary conditions not respected?!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 5, 2010, 12:45
Default Pressure far field boundary conditions not respected?!
  #1
New Member
 
Quentin
Join Date: May 2009
Posts: 22
Rep Power: 8
Bedotto is on a distinguished road
Hello everyone,

I'm working on the expansion of a thermical jet of a motor. To do this I've created a mesh in 2d of the profile of this motor (see the scheme about boundary attached)). But I have an odd issue. The parameters choosen of the pressure far field boundary conditions are not respected. Here an example: I put axial component=1 et radial component=0 but after many iterations when I plot velocity vectors on theses pressure far field boundary I get vectors which haven't the same components that I fixed in parameters panel.

I've tried to modify the mesh on boundary conditions (more or less coarsed), and I tried to expand the limits of my numerical domain but I still have the same problem. I really don't understand the origin of this problem. Does anyone here have faced this kind of problem with Fluent?

(I work in axisymmetric with Spalart Almaras.)

My best regards

Quentin
Attached Images
File Type: jpg SchemeBoundary.jpg (15.5 KB, 31 views)
Bedotto is offline   Reply With Quote

Old   August 5, 2010, 15:07
Default
  #2
Member
 
Join Date: Apr 2009
Posts: 38
Rep Power: 8
doki is on a distinguished road
hi
are you using the cartesian or radial components?
I have had such a problem and I realized thad fluent does not identify the radial and axial directions as we see!
I have fixed the problem using cartesian components of the flow.
So I guess that would be helpful to set the direction in cartesian coordinates.
doki is offline   Reply With Quote

Old   August 5, 2010, 21:39
Default
  #3
New Member
 
Dong Liang
Join Date: Jan 2010
Location: Shanghai, China
Posts: 12
Rep Power: 7
davedong is on a distinguished road
doki is correct.
i get some tricks for this problem. the pressure-far-field bound is pretty, just seems... if your mesh is narrow or unreasonbale, reversed flow and oddy boundary data will crazy you.
you can build the mesh wisely and widely enough (even in the supersonic aircraft problem, the width of tunnel is just 30 times than the wings.). then, you can set the bound as wall.
davedong is offline   Reply With Quote

Old   August 16, 2010, 03:30
Default
  #4
New Member
 
Quentin
Join Date: May 2009
Posts: 22
Rep Power: 8
Bedotto is on a distinguished road
doki: I would like to use cartesian coordinates too but because I work in axis symmetry, I've not the choice, I have to work with axial and radial coordinates when I define the direction of velocity on far field pressure boundary conditions. It seems I can't work with cartesian coordinates. Or am I wrong?

davedong: I'm not sure to understand: I should "stretch" my mesh, that's what you mean? Or the contrary?
Bedotto is offline   Reply With Quote

Old   August 17, 2010, 04:42
Default
  #5
New Member
 
Dong Liang
Join Date: Jan 2010
Location: Shanghai, China
Posts: 12
Rep Power: 7
davedong is on a distinguished road
hi,
i'm sorry for your misunderstanding. english is not my native language.
i mean maybe you can stretch your computing domain. if it is big enough, the boundary set is not determinative.
davedong 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
CFX doesn't continue calculation... mactech001 CFX 6 November 15, 2009 22:25
Pressure boundary conditions Vijay FLUENT 2 January 14, 2009 13:24
Neumann pressure BC and velocity field Antech Main CFD Forum 0 April 25, 2006 02:15
Please help with flow around car modelling! Tudor Miron CFX 17 March 19, 2004 20:23
Boundary conditions? Tom Main CFD Forum 0 November 5, 2002 02:54


All times are GMT -4. The time now is 19:20.