# how can i give a boundary condition with pressure and velocity together

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 December 9, 2010, 16:04 how can i give a boundary condition with pressure and velocity together #1 New Member   Join Date: Nov 2010 Posts: 9 Rep Power: 8 hi everyone inlet boundary condition= pressure 10Pa and velocity 10m/s outlet boundary condition= pressure 10Pa and velocity 10 m/s how we give a boundary pressure and velocity conditions together? thanks thanks thanks

 December 9, 2010, 21:02 #2 Senior Member   Real Name :) Join Date: Jan 2010 Location: United States Posts: 193 Rep Power: 8 akhenathon, See my post to your same question in another thread. Regards, ComputerGuy

 April 24, 2012, 17:03 #3 Member   Join Date: Apr 2009 Posts: 93 Rep Power: 9 ComputerGuy, would you be able to post a link to the thread you are referring... Many thanks

April 24, 2012, 17:52
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two boundary condition on an edge or face

I think this person was trying to over-prescribe the boundary conditions for the system.

Regards,
ComputerGuy

Quote:
 Originally Posted by jpo ComputerGuy, would you be able to post a link to the thread you are referring... Many thanks

 April 24, 2012, 18:04 #5 Member   Join Date: Apr 2009 Posts: 93 Rep Power: 9 I have seen people deal with a similar problem where one needs to set pressure and certain velocity vector at inlet while performing a compressible flow calculation... In a vortex tube calculation, Skye et al (Int. J. Refrig.) made a small-area anular opening at one end of a pipe, then defined the vector direction in cyllindrical coordinates. A high enough inlet pressure on the small area inlet gave the nearly sonic inlet velocity they needed. They adjusted the area until the mass flux was also what was expected to be reasonable. If there are any other ideas how to achieve a similar scenario flux/pressure/velocity vector, I'd be very interested to read about it

April 24, 2012, 18:23
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Just to be clear, the original poster asked how to set BOTH the pressure and velocity (mass flow) at BOTH the inlet and outlet. Perhaps I'm missing something, but isn't that generally an overspecified problem?

If you're OK with performing an iterative calculation to solve for the pressure and mass flow, that's a whole other question. However, I see no way to prescribe them as boundary conditions.

ComputerGuy

Quote:
 Originally Posted by jpo I have seen people deal with a similar problem where one needs to set pressure and certain velocity vector at inlet while performing a compressible flow calculation... In a vortex tube calculation, Skye et al (Int. J. Refrig.) made a small-area anular opening at one end of a pipe, then defined the vector direction in cyllindrical coordinates. A high enough inlet pressure on the small area inlet gave the nearly sonic inlet velocity they needed. They adjusted the area until the mass flux was also what was expected to be reasonable. If there are any other ideas how to achieve a similar scenario flux/pressure/velocity vector, I'd be very interested to read about it

 April 24, 2012, 18:32 #7 Member   Join Date: Apr 2009 Posts: 93 Rep Power: 9 I agree with your reasoning... My post was a bit of a diversion; I wanted to make the point that to define pressure + velocity vector on an inlet boundary takes planning of the area etc

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