CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > CFX

Periodicity momentum instead of axial momentum

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

LinkBack Thread Tools Display Modes
Old   August 3, 2009, 03:55
Default Periodicity momentum instead of axial momentum
New Member
Join Date: Aug 2009
Posts: 1
Rep Power: 0
omez is on a distinguished road

I'm new in the community and I've got a qustion about the use of periodic boundary conditions.
I'm trying to simulate a combustion chamber. Since the chamber is rotationally symetric I use just a piece of 4 degrees of the chamber together with periodic BCs. The mesh has 3-4 cell in the tangantial direction.
I'm solving the problem for steady state. Also the problem neither is influenced by the mesh quality (I have done a mesh study already) nor to a certain location in the fluid domain.
Also, by using symetric BCs the simulation is stable.
I suspect the periodic BCs to make the simulation instable.


The solution starts to get a angular momentum. Beginning from the outlet it propagats along the axis into the combustion chamber.
The solution then starts to get Mach-numbers of the order of 5-10.

If someone had/has the same problems and/or has a good idea for the solution, please let me know.


omez is offline   Reply With Quote

Old   August 3, 2009, 18:59
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,336
Rep Power: 110
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough

In the real world, what is used to stop the flow rotating? You should put the devices in the model to stop it rotating. If you know the flow does not rotate then use symmetry boundaries and forget about the problems with periodic boundaries. Alternately you could put a directional source term in to damp the rotational component - but I would only do this after a thorough check of your simulation to see what is creating the rotation in the first place (ie, two wrongs don't make a right).

Glenn Horrocks
ghorrocks is offline   Reply With Quote


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
SIMPLE momentum in cylindrical coordinates TerraVici Main CFD Forum 4 April 9, 2012 05:22
Pressure jump and momentum source Tanya FLUENT 1 June 4, 2009 15:22
Momentum Source in an accelerating frame fakir CFX 7 December 2, 2006 05:00
no enthalpy change across the momentum source Atit Koonsrisuk CFX 2 December 19, 2005 03:33
Nonstaggered Grids and Momentum Interpolations S. Wang Main CFD Forum 3 March 2, 2001 14:44

All times are GMT -4. The time now is 22:20.