pipe cfd with pressure drop

umbsab988 · May 15, 2018, 08:37

Hello,
I have a pipe with a series of orefice plates and they have to give me a pressure drop of 30 bar ( from 34bar to 4bar). My aim is the mass flow rate. The pipe's diameter is of 60 mm and the orefices holes have a diameter 7mm up to 14mm (6 plates). The lenght of the pipe is 600mm initial velocity is 1.7 m/s.What kind of boundary conditions and input should I give, using a k-omega model?

LuckyTran · May 15, 2018, 19:00

What is initial velocity? You mean velocity at the inlet? If you know the inlet velocity 1.1 m/s and pressure is 34bar, you pretty much already know the mass flow rate. What is the point of doing CFD?

To get a fixed pressure drop you'd set at the outlet, pressure of 3 bar. At the inlet, pressure of ~34 bar. Depending on your model you may be able to specify the static pressure or sometimes the stagnation pressure. Also you need an inlet static/stagnation temperature.

For k and omega, it depends what is upstream of your setup. But with a bunch of orifice plates I bet it does not influence the solution much.

piu58 · May 16, 2018, 01:58

Form my experience, setting two pressures as b.c. is less stable than setting an inlet velocity. If your calculation time is not too high you may consider setting this bc. and change the velocity until you get the pressure drop you already know.

umbsab988 · May 16, 2018, 04:41

hi,
the temperature inlet is 20C° while the temperature outlet is 14 C°. I cannot use velocity inlet because the Mach number is very low at inlet and very high at outlet so it's a compressible folw and the Re=2.6e5. The time calculation is high. I use "gauge total pressure"= 3400058 Pa (absolute) and Supersonic/Initial Gauge Pressure =3400000Pa (absolute) at inlet (the inlet is positioned at a distance of 10*diameter from first plate) and 400000 Pa (absolute) at outlet

umbsab988 · May 17, 2018, 05:17

if I use velocity inlet, what initial/supersonic gauge pressure and outflow gauge pressure I have to use at inlet? and at outlet?

May 15, 2018, 08:37	pipe cfd with pressure drop	#1
umbsab988 New Member NA Join Date: May 2018 Posts: 8 Rep Power: 8	Hello, I have a pipe with a series of orefice plates and they have to give me a pressure drop of 30 bar ( from 34bar to 4bar). My aim is the mass flow rate. The pipe's diameter is of 60 mm and the orefices holes have a diameter 7mm up to 14mm (6 plates). The lenght of the pipe is 600mm initial velocity is 1.7 m/s.What kind of boundary conditions and input should I give, using a k-omega model?

May 16, 2018, 01:58		#3
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	Form my experience, setting two pressures as b.c. is less stable than setting an inlet velocity. If your calculation time is not too high you may consider setting this bc. and change the velocity until you get the pressure drop you already know. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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May 15, 2018, 19:00		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,747 Rep Power: 66	What is initial velocity? You mean velocity at the inlet? If you know the inlet velocity 1.1 m/s and pressure is 34bar, you pretty much already know the mass flow rate. What is the point of doing CFD? To get a fixed pressure drop you'd set at the outlet, pressure of 3 bar. At the inlet, pressure of ~34 bar. Depending on your model you may be able to specify the static pressure or sometimes the stagnation pressure. Also you need an inlet static/stagnation temperature. For k and omega, it depends what is upstream of your setup. But with a bunch of orifice plates I bet it does not influence the solution much.

May 16, 2018, 04:41		#4
umbsab988 New Member NA Join Date: May 2018 Posts: 8 Rep Power: 8	hi, the temperature inlet is 20C° while the temperature outlet is 14 C°. I cannot use velocity inlet because the Mach number is very low at inlet and very high at outlet so it's a compressible folw and the Re=2.6e5. The time calculation is high. I use "gauge total pressure"= 3400058 Pa (absolute) and Supersonic/Initial Gauge Pressure =3400000Pa (absolute) at inlet (the inlet is positioned at a distance of 10*diameter from first plate) and 400000 Pa (absolute) at outlet

May 17, 2018, 05:17		#5
umbsab988 New Member NA Join Date: May 2018 Posts: 8 Rep Power: 8	if I use velocity inlet, what initial/supersonic gauge pressure and outflow gauge pressure I have to use at inlet? and at outlet?