Pressures problems

cfdhydraulic · February 13, 2012, 18:28

Hi everyone,
I would appreciate if somebody is able to explain the meaning of Operating Pressure, and Gauge Pressure and Supersonic/initial pressure...

I mean, I know the meaning of it but I never know how to set when solving a problem in Fluent.

I've looked over Fluent Help but it's still not clear to me.

Operating pressure is atmospheric pressure? what about supersonic?? what should I set under Gauge pressure textbox??

For instance, let's consider a pipe with a air stream at 6 bars, so that, what would I set as a gauge pressure, operating conditions, and supersonic/initial pressure...??

thanks in advanced

niaz · February 15, 2012, 04:45

operating pressure is used as refrence for solving pressre equation.
and it should be local pressure. gauge pressure is the difference of your abs pressure to operating pressure.
and supersonic pressure is used for compressible flow and it has its own meaning.

Zigainer · February 15, 2012, 06:47

If you choose to define the density using the ideal gas law for an incompressible flow, the solver will compute the density as density = operating pressure / (R_gas * Temperature). In this form, the density depends only on the operating pressure and not on the local relative pressure field.
So for the operating pressure you should use a reasonable value. In your example it would be 6bar. All other defined pressures are gauge pressures. So let's say your pressure at the outlet would be 5bar, than in the BC your gauge pressure would be -1bar.

February 13, 2012, 18:28	Pressures problems	#1
cfdhydraulic Member andres Join Date: Sep 2010 Posts: 44 Rep Power: 15	Hi everyone, I would appreciate if somebody is able to explain the meaning of Operating Pressure, and Gauge Pressure and Supersonic/initial pressure... I mean, I know the meaning of it but I never know how to set when solving a problem in Fluent. I've looked over Fluent Help but it's still not clear to me. Operating pressure is atmospheric pressure? what about supersonic?? what should I set under Gauge pressure textbox?? For instance, let's consider a pipe with a air stream at 6 bars, so that, what would I set as a gauge pressure, operating conditions, and supersonic/initial pressure...?? thanks in advanced

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February 15, 2012, 04:45		#2
niaz Senior Member A_R Join Date: Jun 2009 Posts: 122 Rep Power: 16	operating pressure is used as refrence for solving pressre equation. and it should be local pressure. gauge pressure is the difference of your abs pressure to operating pressure. and supersonic pressure is used for compressible flow and it has its own meaning.

February 15, 2012, 06:47		#3
Zigainer Senior Member Join Date: May 2011 Location: Germany Posts: 130 Rep Power: 14	If you choose to define the density using the ideal gas law for an incompressible flow, the solver will compute the density as density = operating pressure / (R_gas * Temperature). In this form, the density depends only on the operating pressure and not on the local relative pressure field. So for the operating pressure you should use a reasonable value. In your example it would be 6bar. All other defined pressures are gauge pressures. So let's say your pressure at the outlet would be 5bar, than in the BC your gauge pressure would be -1bar.