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-   -   for help about cfx boundary condition settting (http://www.cfd-online.com/Forums/cfx/90175-help-about-cfx-boundary-condition-settting.html)

rainning139 July 3, 2011 09:11

for help about cfx boundary condition settting
 
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.;)

ghorrocks July 3, 2011 19:05

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.

rainning139 July 3, 2011 21:26

Quote:

Originally Posted by ghorrocks (Post 314541)
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?
HOPE for your answer.THANKS AGAIN!

ghorrocks July 4, 2011 06:25

If you are taking a 2D slice for a model then you need to reduce the flow rate according to your sector angle.

rainning139 July 4, 2011 20:45

Quote:

Originally Posted by ghorrocks (Post 314612)
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:)


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