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

simple 3D pipe flow diverges with icoFoam

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 23, 2011, 10:24
Default simple 3D pipe flow diverges with icoFoam
  #1
Rol
New Member
 
Roland
Join Date: Jul 2010
Posts: 8
Rep Power: 16
Rol is on a distinguished road
Hello!

I am trying to get grips with OpenFoam. I set up a really EASY case. It is some kind of straight tube. The simulation should be easy, but after 6 iterations, icoFoam diverges. I use the solver settings from the elbow testcase.
Possible problems i thought on:
mesh: it is really fine, much too fine (just to be sure)
time step: is also set really small (dx=2/40 m, U=1m/s -> dt=0.05 should be sufficient, i set it to 0.01)
boundary conditions: inlet with Velocity set to 1 m/s; p at outlet set to 0 Pa. The rest is wall. I checked BC several times, and i find no mistake

I include the test case.

the case is ready to

blockMesh

and

icoFoam

you will see, it diverges after 6 time steps.

any hint is really appreciated!

Roland
Attached Files
File Type: zip tube.zip (4.5 KB, 58 views)
Rol is offline   Reply With Quote

Old   June 23, 2011, 14:33
Default
  #2
Rol
New Member
 
Roland
Join Date: Jul 2010
Posts: 8
Rep Power: 16
Rol is on a distinguished road
I think my test case was not as simple as i thought. The geometry of the tube leads to secondary flows. however, i found out convergence with upwind divScheme is much better.
Rol is offline   Reply With Quote

Old   June 24, 2011, 10:55
Default
  #3
Senior Member
 
Join Date: Jun 2011
Posts: 163
Rep Power: 15
mechy is on a distinguished road
Quote:
Originally Posted by Rol View Post
I think my test case was not as simple as i thought. The geometry of the tube leads to secondary flows. however, i found out convergence with upwind divScheme is much better.

I think the length of your tube in y direction is very small and you can not impose zeroGradient at the outlet I suggest you, to increase your length ten times of square root of section area
mechy is offline   Reply With Quote

Old   June 24, 2011, 13:03
Default
  #4
Rol
New Member
 
Roland
Join Date: Jul 2010
Posts: 8
Rep Power: 16
Rol is on a distinguished road
mechy, thanks, although i checked the solver conditions several times i payed less attention on the geometry itself. It makes sense that the short tube interferes with the zeroGradient boundary condition. Thanks!
Rol is offline   Reply With Quote

Old   June 25, 2011, 05:28
Default
  #5
Senior Member
 
Join Date: Jun 2011
Posts: 163
Rep Power: 15
mechy is on a distinguished road
Quote:
Originally Posted by Rol View Post
mechy, thanks, although i checked the solver conditions several times i payed less attention on the geometry itself. It makes sense that the short tube interferes with the zeroGradient boundary condition. Thanks!

is your problem solved with increasing length of tube ?
mechy is offline   Reply With Quote

Old   June 27, 2011, 18:02
Default
  #6
Rol
New Member
 
Roland
Join Date: Jul 2010
Posts: 8
Rep Power: 16
Rol is on a distinguished road
yes, increasing the length solves the problem. Also i set the time step very low. maybe setting pressure boundary condition instead of velocity at inlet would also help convergence. but it works for me. thanks
Rol is offline   Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pipe flow with obstacle - HELP Min FLUENT 6 January 31, 2017 15:28
Disturbed flow field at outlet boundary (Multiphase flow through pipe) Michiel CFX 17 April 21, 2010 11:14
simple pipe flow question arkur CFX 1 July 11, 2008 17:32
Pressure Drop - Please Help - Simple Pipe Flow Joe A. FLUENT 2 April 23, 2007 08:50
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 10:11


All times are GMT -4. The time now is 15:04.