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

Flow Reversal at the inlet

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 15, 2010, 04:34
Default Flow Reversal at the inlet
  #1
New Member
 
selim
Join Date: Sep 2009
Location: UK
Posts: 19
Rep Power: 16
salihovic is on a distinguished road
I have analyzed a flow field over a cylinder in pulsating flow (unsteady flow). At the inlet, we have periodic forcing with high amplitudes.

Velocity inlet: u(t)=u0+2*u0*sin(w*t);

At some time the flow becomes reversal at the inlet because the time dependent amplitude is twice the steady state amplitude (u0). We have implied a velocity inlet for the inlet boundary condition.

The solver gives a warning about the flow reversal.

My question is about:

How does the CFX solver face this problem?
Thanks in advance,
salihovic is offline   Reply With Quote

Old   July 15, 2010, 07:47
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
When you specify a velocity boundary with reverse flow does the solver construct walls to stop it? I am not sure - if it does not then you are fine and just proceed.
ghorrocks is offline   Reply With Quote

Old   July 15, 2010, 08:03
Default
  #3
New Member
 
selim
Join Date: Sep 2009
Location: UK
Posts: 19
Rep Power: 16
salihovic is on a distinguished road
Yes.

The solver gives me a warning. Something like ''A wall is constructed.....flow reversal...'' But, I am happy with my results.

How can I interpret the construction of the wall? What does it mena physically? Is this not anymore a BC that I am imposing (velocity inlet)?

At the outlet I a have pressure outlet BC (in this case I may also use an opening type BC)

Is there any documentation of CFX about that issue?

Thanks a lot,
salihovic is offline   Reply With Quote

Old   July 15, 2010, 11:50
Default
  #4
Senior Member
 
Matthias Voß
Join Date: Mar 2009
Location: Berlin, Germany
Posts: 449
Rep Power: 20
mvoss is on a distinguished road
yap.
cfx is building artificial walls, since it is an "inlet" the inwards face normal has to be same like the vel.components.

Try an opening with specified vel.comp. and set Expert Parameter-->Discret.-->Misc.--> build art.walls =false

this should do it.

neewbie
mvoss is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Maintaining Static Pressure at Fluid Flow Inlet cdevalve FLUENT 3 January 14, 2012 01:11
Problems modeling subsonic engine air inlet with flow separation TWaung CFX 2 March 29, 2009 19:42
inlet mass flow rate BC manu FLUENT 0 February 5, 2008 14:24
velocity or mass flow inlet? Silvia FLUENT 1 August 12, 2005 14:55
pressure inlet in incompressible flow dirk FLUENT 2 June 22, 2005 14:27


All times are GMT -4. The time now is 15:45.