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

wall condition for extended outlet

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 6, 2010, 10:52
Default wall condition for extended outlet
  #1
New Member
 
Join Date: Jun 2009
Posts: 20
Rep Power: 8
kuhbuh is on a distinguished road
Hi everyone!

In my calculation, I extended the outlet to prevent inflow as recommend in the CFX documentation. I just want to ask if it's appropriate to assign the wall of the additional region as free slip (no slip in the main domain) so as not to further retard the flow. Is this correct? thanks a lot guys!

kuh
kuhbuh is offline   Reply With Quote

Old   April 6, 2010, 12:55
Default
  #2
Member
 
Dmitry Volkind
Join Date: Jan 2010
Location: Chelyabinsk, Russia
Posts: 58
Rep Power: 7
dvolkind is on a distinguished road
Depends on what You are modelling. Why don't You want to retard the flow?
dvolkind is offline   Reply With Quote

Old   April 6, 2010, 13:19
Default
  #3
New Member
 
Join Date: Jun 2009
Posts: 20
Rep Power: 8
kuhbuh is on a distinguished road
Hi! Thank you for your reply. I'm simulating 2 phase flow and there is some recirculation near the outlet. My outlet condition is based on experimental data and I'm afraid that further extending it would have some inaccuracy.
kuhbuh is offline   Reply With Quote

Old   April 6, 2010, 13:35
Default
  #4
Member
 
Dmitry Volkind
Join Date: Jan 2010
Location: Chelyabinsk, Russia
Posts: 58
Rep Power: 7
dvolkind is on a distinguished road
What are Your BCs?
dvolkind is offline   Reply With Quote

Old   April 6, 2010, 13:37
Default
  #5
New Member
 
Join Date: Jun 2009
Posts: 20
Rep Power: 8
kuhbuh is on a distinguished road
My BCs are velocity in and pressure out. Tnx!
kuhbuh is offline   Reply With Quote

Old   April 6, 2010, 13:58
Default
  #6
Member
 
Dmitry Volkind
Join Date: Jan 2010
Location: Chelyabinsk, Russia
Posts: 58
Rep Power: 7
dvolkind is on a distinguished road
Then moving outlet further away most likely won't affect accuracy. With inlet speed specified You will get a higher inlet pressure then You would expect without moving the boundary. Thus, absolute pressure values might slightly change, but basically pressure differences are important. So, if the absolute pressure level does not have much effect for Your problem and extending the domain won't introduce new geometry features then I think it's OK to move the boundary.

By the way, wall shear stress at non-sleep wall is not the only cause of pressure loss, so there's no guarantee that You won't get any pressure drop in free-slip region.
dvolkind is offline   Reply With Quote

Old   April 6, 2010, 14:02
Default
  #7
New Member
 
Join Date: Jun 2009
Posts: 20
Rep Power: 8
kuhbuh is on a distinguished road
Thank you very much for the input! I'll run few more simulations and check if there's effect. Thanks again!
kuhbuh is offline   Reply With Quote

Old   April 6, 2010, 18:41
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,651
Rep Power: 84
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
The best way to look at it is you want to model what the experimentalists measured. If they had a long runner downstream of the test section, then model that. If they dumped it into a big tank then model that.
ghorrocks is offline   Reply With Quote

Old   April 8, 2010, 10:30
Default
  #9
New Member
 
Join Date: Jun 2009
Posts: 20
Rep Power: 8
kuhbuh is on a distinguished road
Thanks again Sir Glenn! I'll take note of that.
kuhbuh is offline   Reply With Quote

Reply

Tags
outlet wall, slip

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
UDS problem with wall boundary condition Alex F. FLUENT 14 August 6, 2014 05:08
Outlet boundary condition colen CFX 6 March 8, 2010 23:49
Transient outlet boundary condition problem jwillie2000 CFX 1 December 7, 2009 18:07
how to set up a wall boundary condition according to calculated wall shear stress? gameoverli OpenFOAM Pre-Processing 1 May 21, 2009 08:28
How can define our Outlet Condition? POR FLUENT 0 October 11, 2002 06:24


All times are GMT -4. The time now is 09:09.