# for help about cfx boundary condition settting

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

 July 3, 2011, 09:11 for help about cfx boundary condition settting #1 New Member   tao Join Date: Jul 2011 Posts: 5 Rep Power: 8 Dear all, I want to simulate the gas flow in a pipe using cfx ,gas at the inlet positon is 15000Pa(Guage pressure),velocity is 3m/s and i mean to know the outlet preesure.As a new learner ,I need your help now.I'm puzzled how to set the boundary conditons.Please give me the answer if you knows.Thanks a lot.

 July 3, 2011, 19:05 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,083 Rep Power: 109 You have overspecified the inlet. You cannot define both velocity and pressure at an inlet. I would convert the velocity to a flow rate, and apply the flow rate to the outlet. Then you can use 15kPa at the inlet and a mass/volume flow rate outlet boundary.

July 3, 2011, 21:26
#3
New Member

tao
Join Date: Jul 2011
Posts: 5
Rep Power: 8
Quote:
 Originally Posted by ghorrocks You have overspecified the inlet. You cannot define both velocity and pressure at an inlet. I would convert the velocity to a flow rate, and apply the flow rate to the outlet. Then you can use 15kPa at the inlet and a mass/volume flow rate outlet boundary.
\Thank you for your answer.i will have a try .however I still have a question.NOW I want to use 2D model and the diameter of the pipe decreased in the middle, just like a Venturi tube.I guess the velocity at the outlet may be different from the velocity of the inlet,because the pressure change at the outlet,then the volumne flow rate will change.
I have used 15kPa at the inlet and the total mass flow rate of the 3D whole pipe as the mass flow rate of the 2D model,then I found the velocity is big abnormally,about 2900m/s. IS the mass flow rate improper?

 July 4, 2011, 06:25 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,083 Rep Power: 109 If you are taking a 2D slice for a model then you need to reduce the flow rate according to your sector angle.

July 4, 2011, 20:45
#5
New Member

tao
Join Date: Jul 2011
Posts: 5
Rep Power: 8
Quote:
 Originally Posted by ghorrocks If you are taking a 2D slice for a model then you need to reduce the flow rate according to your sector angle.
THANKS.I will have a try

 Tags boundary conditions, cfx 12.1

 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 jannnesss CFX 5 February 25, 2011 17:24 Pankaj CFX 9 November 23, 2009 05:05 Michele Cagna CFX 3 February 22, 2007 16:52 Matt Umbel Main CFD Forum 0 January 11, 2002 11:06 boing Main CFD Forum 1 January 6, 2002 17:53

All times are GMT -4. The time now is 15:27.