# Boundaries definition

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

 January 15, 2010, 07:41 Boundaries definition #1 Senior Member   Join Date: Jan 2010 Posts: 110 Rep Power: 8 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

January 16, 2010, 00:15
#2
Super Moderator

Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,704
Rep Power: 98
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?

 January 16, 2010, 15:12 #3 Senior Member     Fatema Zandi Goharrizi Join Date: Mar 2009 Posts: 156 Rep Power: 9 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

January 16, 2010, 15:18
#4
Senior Member

Fatema Zandi Goharrizi
Join Date: Mar 2009
Posts: 156
Rep Power: 9
Quote:
 Originally Posted by ghorrocks 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.

 January 16, 2010, 17:13 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,704 Rep Power: 98 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.

 January 18, 2010, 05:52 #6 Senior Member   Join Date: Jan 2010 Posts: 110 Rep Power: 8 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

 January 18, 2010, 06:00 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,704 Rep Power: 98 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.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Paolo STAR-CD 8 October 23, 2009 12:00 Eran FloEFD, FloWorks & FloTHERM 3 August 11, 2009 04:23 PK FLUENT 0 July 12, 2007 11:58 swetha FLUENT 1 November 26, 2006 23:02 Subhra Datta Main CFD Forum 2 November 24, 2003 14:11

All times are GMT -4. The time now is 04:19.