# How to Define Pressure Boundary Conditions?

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 May 5, 2000, 05:16 How to Define Pressure Boundary Conditions? #1 Sheenu Guest   Posts: n/a Hi, I'm working in PHOENICS. I want to know how to define pressure boundary conditions - at inlet to the flow domain. There's something called Reference pressure to be set in PHOENICS - Should it be Atmospheric pressure? I'd be grateful if anyone can help me.

 May 5, 2000, 07:59 Re: How to Define Pressure Boundary Conditions? #2 Cfd Guest   Posts: n/a I'm not specifically sure about Phoenix, but if it is like other CFD codes, the reference pressure is simply used to offset all the pressures to preserve precision in pressure gradients. For example, it is more accurate numerically to get DELTAP=(1.01-1.005) than DELTAP= (100001.01-100001.005). So for pressures near atmospheric, you set 100000 PA to be the reference pressure, and operate in relative pressures. Clearly, the reference can be any convenient value, not just 1 Atm.

 May 5, 2000, 20:11 Re: How to Define Pressure Boundary Conditions? #3 ral Guest   Posts: n/a I'm an italian student searching something about u_v_p , fem and in general material about the exam I'm studing : Numerical Fluidodynamics.

 May 8, 2000, 10:46 Re: How to Define Pressure Boundary Conditions? #4 Yun Guest   Posts: n/a I think the Reference pressure is for Non-dimension the flowfield, basicly, it is not boundary condition. For the external flows, you can simply take the farfield pressure. For internal flows, Total pressure can be used.

 May 12, 2000, 12:52 Re: How to Define Pressure Boundary Conditions? #5 C.U.D Guest   Posts: n/a (1) J.C.P . Vol 68,p.p.1-24,1987 (2) J.C.P . Vol 89,p.p.439-461,1990 (3) J.C.P . Vol 101,p.p.104-129,1992 (4) J.C.P . Vol 114,p.p.43-55,1994