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

how to consider gravity in CFX

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

Reply
 
LinkBack Thread Tools Display Modes
Old   September 5, 2008, 17:51
Default how to consider gravity in CFX
  #1
shrimp
Guest
 
Posts: n/a
For a pump simulation, the roation axis is set as Z Dirn. As the medium is water, I think gravity should be considered. But when I set "Buoyancy" -> Gravity Y Dirn: -9.8 m s^-2, Gravity X,Z Dirn: 0. I got a error message shown as below. I think it is werid. Because according to the momentum equation, gravity can be added even it is not aligned with rotation axis. Am I right? and if so, how can I add gravity in steady-state?

| ERROR #001100279 has occurred in subroutine ErrAction. | | Message: This simulation involves a gravity vector which is not aligned with the rotation axis. This is valid only if the simulation type is transient, but it is currently set to steady-state. Please change the setup accordingly
  Reply With Quote

Old   September 7, 2008, 19:38
Default Re: how to consider gravity in CFX
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

If you are doing a frozen rotor multiple frames of reference simulation then obviously you cannot have the gravity vector in any direction except the rotation vector as it cannot be averaged over the rotation.

Why do you need to include gravity? Can't you do it just by putting a inlet and outlet pressure difference?

Glenn Horrocks
  Reply With Quote

Old   September 8, 2008, 02:59
Default Re: how to consider gravity in CFX
  #3
shrimp
Guest
 
Posts: n/a
Thanks for your reply. Yes, I do use frozen rotor multiple frames of reference. I thought frozen rotor just keeps the relative position unchange, but no idea on how this would affect the gravity vector. Well, I can not understand why this type of interface doesn't allow the variables that can not be averaged over the rotation? How can I find more information on this? Thanks again!
  Reply With Quote

Old   September 8, 2008, 18:57
Default Re: how to consider gravity in CFX
  #4
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

The various MFR options (multiple frames of reference) options are discussed in the documentation.

If you want to include gravity in an impeller simulation with gravity not along the impeller shaft you will have to run a full transient-rotor stator simulation. You would only do this if you were modelling priming a pump say, where there was lots of air and water around.

For general running of the pump bouyancy has no effect, except to create a head for the pump to push against, and that is more easily done with pressure boundary conditions.

Glenn Horrocks
  Reply With Quote

Old   September 8, 2008, 20:41
Default Re: how to consider gravity in CFX
  #5
shrimp
Guest
 
Posts: n/a
Thanks!!
  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
Electronics Enclosure Analysis with CFX Simulation Engineer CFX 1 April 22, 2009 11:08
RE: Applying forces / Center of Gravity in CFX Janusz CFX 1 November 16, 2008 20:37
Considering Gravity effect(or Hydradynamic) in CFX klarke CFX 7 October 2, 2006 03:53
CFX 10's solutions differ from CFX 5.7's Atit Koonsrisuk CFX 4 July 26, 2006 11:59
CFX 4.4 installation problem Pandu Sattvika CFX 1 December 1, 2001 05:07


All times are GMT -4. The time now is 10:33.