# Basic boundary condition question

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 September 17, 2008, 15:04 Hi all, Given that the outw #1 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 703 Rep Power: 13 Hi all, Given that the outward drawn unit normal to inlet and outlet boundaries point parallel to the x-direction, are the following the only conditions that need to be satisfied at these boundaries? For a fixed velocity inlet, u = fixed value v = fixed value (dp/dx) = 0.0 For a fixed pressure outlet, p = fixed value du/dx = 0.0 dv/dx = 0.0 Where: In 2D: U = [u,v] (u and v are the two components of velocity vector U) and assume that 'd' represents the partial derivative symbol. I would appreciate if someone can point out if I am incorrect or missing anything here. Thanks for your help.

 September 18, 2008, 13:02 Anyone? Even a simple Yes or N #2 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 703 Rep Power: 13 Anyone? Even a simple Yes or No will suffice.

 September 18, 2008, 13:15 For incompressible laminar flo #3 Senior Member   Xiaofeng Liu Join Date: Mar 2009 Location: State College, PA, USA Posts: 118 Rep Power: 9 For incompressible laminar flow, Yes __________________ Xiaofeng Liu, Ph.D., P.E., Assistant Professor Department of Civil and Environmental Engineering Penn State University 223B Sackett Building University Park, PA 16802 Web: http://water.engr.psu.edu/liu/

 September 19, 2008, 10:59 Thanks Xiaofeng. #4 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 703 Rep Power: 13 Thanks Xiaofeng.

 October 1, 2008, 17:05 For a plain channel or pipe fl #5 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 703 Rep Power: 13 For a plain channel or pipe flow, dp/dx = 0 at the inlet boundary does not seem to make sense. The pressure should be allowed to change in the X-direction. Can anyone comment on that?

 October 1, 2008, 19:56 Thanks very much for that resp #7 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 703 Rep Power: 13 Thanks very much for that response Niels. You've brought some interesting facts to my attention. I'll try and dig up more information on this.

 October 14, 2008, 00:25 Hello People, I am have a s #8 Member   Mahendra Join Date: Mar 2009 Location: Pune, Maharashtra, India Posts: 65 Rep Power: 9 Hello People, I am have a small doubt regarding pressure boundary condition. In Fluent i have specified -1500 Pa gauge (negative) boundary condition at outlet. In OpenFOAM what boundary condition should i give. like this or something different? outlet { type fixedValue; value -1225; // (-1500/1.225) pressure/density since units of pressure are [0 2 -2 0 0 0 0]. } --

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