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

Sinusoidal velocity settings ?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 3, 2008, 05:54
Default Sinusoidal velocity settings ?
  #1
Adenlan
Guest
 
Posts: n/a
Hi everyone,

I'm trying to setup a sinusoidal current in cfx but it seems I don't use the proper way. I set the simulation on transient mode in inlet boundary I use a cartesian velocity with expression : U=0 V=0 W=W [m s^-1]*sin(pi[rad s^-1]*t) and initial conditions set to 0 . The problem is that it does not converge instead each iteration I have this message :

****** Notice ****** | A wall has been placed at portion(s) of an OUTLET boundary condition (at 76.5% of the faces, 77.1% of the area)to prevent fluid from flowing into the domain. The boundary condition name is: outlet.The fluid name is: Water. If this situation persists, consider switching to an Opening type boundary condition instead.

Please someone help me !
  Reply With Quote

Old   November 3, 2008, 06:12
Default Re: Sinusoidal velocity settings ?
  #2
Adenlan
Guest
 
Posts: n/a
Don't mind, my error is too obvious
  Reply With Quote

Old   November 4, 2008, 07:47
Default Re: Sinusoidal velocity settings ?
  #3
underGroundMan
Guest
 
Posts: n/a
Set your outlet to 1 atm and reference pressure to zero.
  Reply With Quote

Old   November 6, 2008, 13:13
Default Re: Sinusoidal velocity settings ?
  #4
Amod
Guest
 
Posts: n/a
By definition, Inlet Boundary condition should have flow always into the domain and Outlet Boundary condition should have flow always out of the domain.

By specifying inlet velocity profile as a function of time, you are changing the magnitude and direction of flow at the inlet boundary. This is not acceptable mathematically!

You may have to use moving boundary problem such as movement of Piston in an internal combustion engine.

Hope it clears! Amod
  Reply With Quote

Old   November 7, 2008, 04:49
Default Re: Sinusoidal velocity settings ?
  #5
Rui
Guest
 
Posts: n/a
Hi,

Why is it not acceptable mathematically?

What happens when one defines a negative (outwards) velocity on an Inlet Boundary in CFX?

P.S. There's nothing wrong in changing the magnitude of the flow at an Inlet Boundary, is there?
  Reply With Quote

Old   November 12, 2008, 07:02
Default Re: Sinusoidal velocity settings ?
  #6
underGroundMan
Guest
 
Posts: n/a
I agree Rui. I have used time varying boundary condition many times and it works fine.
  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
UDF error - parabolic velocity profile - 3D turbine Zaqie Fluent UDF and Scheme Programming 8 May 11, 2014 08:34
how to compute relative velocity from absolute? spk Main CFD Forum 3 July 9, 2010 08:42
How to calculate Velocity? Kali Sanjay Phoenics 1 May 1, 2006 13:57
Neumann pressure BC and velocity field Antech Main CFD Forum 0 April 25, 2006 02:15
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 09:11


All times are GMT -4. The time now is 07:06.