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

Boundaries definition

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 15, 2010, 07:41
Default Boundaries definition
  #1
Senior Member
 
Join Date: Jan 2010
Posts: 110
Rep Power: 7
antonio is on a distinguished road
Hi all:

Is there any way in a free-surface model to don`t specify the normal speed in the inlet boundary? Well, of course I need to specify initial values but i don`t want to specify that value (the normal speed) in the boundary. I just want to give an initial height of the water (in the upstream and downstream sections) and I hope that the model converges to some discharge. Is this possible?

How can I create periodic boundary conditions?

Many thanks
antonio is offline   Reply With Quote

Old   January 16, 2010, 00:15
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,958
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
Is there any way in a free-surface model to don`t specify the normal speed in the inlet boundary?
Look in the available options in CFX-Pre. You can also set a pressure.

Quote:
I just want to give an initial height of the water (in the upstream and downstream sections) and I hope that the model converges to some discharge. Is this possible?
No. You can specify the inlet water height but not the outlet.

Quote:
How can I create periodic boundary conditions?
This is described in the documentation. It is also mush easier in V12. Are you using V12?
ghorrocks is offline   Reply With Quote

Old   January 16, 2010, 15:12
Default
  #3
Senior Member
 
zandi's Avatar
 
Fatema Zandi Goharrizi
Join Date: Mar 2009
Posts: 140
Rep Power: 8
zandi is on a distinguished road
Salam = Hi
you can use static pressure or total one
I think I'm working with a project with the same definition for inlet but not periodic
I used static pressure and defined a function in expression. see tutorial 7 , I used the same function for UpPres and put it for static pressure. in this tutorial you can learn how specify the Hd hydraulic head. see expressions and use the step function. learn about it in guide.
I have version 11
good luck
zandi is offline   Reply With Quote

Old   January 16, 2010, 15:18
Default
  #4
Senior Member
 
zandi's Avatar
 
Fatema Zandi Goharrizi
Join Date: Mar 2009
Posts: 140
Rep Power: 8
zandi is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post

No. You can specify the inlet water height but not the outlet.


It is also mush easier in V12. Are you using V12?

salam = hi


in tutorial 7 it used outlet water height if i'm right.
  • could you please tell how much it's different in version 12 from 11?
regards
zandi

Last edited by zandi; January 17, 2010 at 08:03.
zandi is offline   Reply With Quote

Old   January 16, 2010, 17:13
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,958
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
From memory improvements to periodic boundary conditions were made, allowing you to set an inlet and outlet to be linked with specified flow rate or pressure drop or a few other options.
ghorrocks is offline   Reply With Quote

Old   January 18, 2010, 05:52
Default
  #6
Senior Member
 
Join Date: Jan 2010
Posts: 110
Rep Power: 7
antonio is on a distinguished road
Hi All.

Thanks a lot for your suggestions.

Yes ghorrocks I am using V12. I have already saw in the documentation how to set the periodic boundaries (it`s called domain interface isn`t it?). However I still have one question. In the option Interface model I have 3 options : mass flow rate, none and pressure change. At the present moment I have chosed none...Is this a problem?

Setting periodic boundary conditions there is no need to define inlet boundaries with velocities isn`t it?

Zandi, I am going to see tutorial 7.

Regards
antonio is offline   Reply With Quote

Old   January 18, 2010, 06:00
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,958
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
A periodic boundary is a type of domain interface. There are other types as well.

The three options relate to how the flow goes out one end and comes in the other. Mass flow rate means the mass flow will be set to your specified amount. Pressure means the pressure rise/drop over the boundary will be set. None means all flow variable map over.

If your model is one chamber in a cascade of many identical chambers then periodic boundaries can be a good approach. You the use a pressure or mass flow periodic boundary to drive a flow through the domain and you will get the representative flow in the chamber.

In your case I assume you have a mass flow rate, so in this case you will not need to set velocities or fluid heights. However an initial guess which is close may help convergence.
ghorrocks is offline   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
STARCD - inlet boundaries definition in combustion problem Paolo STAR-CD 8 October 23, 2009 12:00
Setting Flow/Pressure Boundaries in Floworks Eran FloEFD, FloWorks & FloTHERM 3 August 11, 2009 04:23
periodic boundaries - flow through a net PK FLUENT 0 July 12, 2007 11:58
Periodic Boundaries in GAMBIT!! swetha FLUENT 1 November 26, 2006 23:02
mass flux correction at outflow boundaries Subhra Datta Main CFD Forum 2 November 24, 2003 14:11


All times are GMT -4. The time now is 19:47.