# what is meant by Operating Pressure in Fluent?

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December 4, 2018, 06:04
#21
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Kushal Puri
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Quote:
 Originally Posted by Federer83 Hi all, Thanks for all your answer. What about if i want to calculate in a bend pipe the pressure losses and the poutlet is 10bar in a incompressible fluid? From what i understood: a) operating pressure= 10 bar b) gauge pressure = 0 bar? Correct? Why my pressure in CFD post is not considering the operating pressure? Thanks
Just try with operating pressure 0 bar, pressure outlet 10 bar and mass flow inlet.

December 4, 2018, 06:23
#22
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Quote:
 Originally Posted by Federer83 Hi all, Thanks for all your answer. What about if i want to calculate in a bend pipe the pressure losses and the poutlet is 10bar in a incompressible fluid? From what i understood: a) operating pressure= 10 bar b) gauge pressure = 0 bar? Correct? Why my pressure in CFD post is not considering the operating pressure? Thanks

real pressure = operating pressure + gauge pressure.
10 bar = 10 bar + 0 bar

So, correct.

And why you don't see it in CFD post: probably because you are not plotting the correct pressure. What CFD post calls "pressure" is the gauge pressure. If you want CFD post to plot the absolute pressure, you have to tell Fluent to save this:
File -> Data file quantities
Under "Additional quantities", select "Absolute pressure". Then save it, and load the new version in CFD post.

 December 4, 2018, 07:10 #23 New Member   Fab Join Date: Dec 2018 Posts: 13 Rep Power: 7 Many thanks Pakk! It worked for the absolute static pressure. What about the total pressure? Why it is still relative? (i know that is only a sum )

 December 4, 2018, 07:11 #24 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 26 Why? Because Ansys chose to define it in such a way...

December 4, 2018, 10:58
#25
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Lucky
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Quote:
 Originally Posted by Federer83 Many thanks Pakk! It worked for the absolute static pressure. What about the total pressure? Why it is still relative? (i know that is only a sum )

Because all pressures in fluent are gauge pressures. The only reason the absolute static pressure exists as a predefined variable is because that's the thermodynamic pressure you use in the equation of state.

 December 23, 2019, 02:54 #26 Senior Member   FHydro Join Date: Jan 2013 Posts: 197 Rep Power: 13 Hi. What is the effect of operating boundary on pressure outputs for example in contours? I simulated a vof model with pressure inlet boundary with gauge total pressure 0 and operating pressure 101325 Pa. When I see the contours of static pressure, it shows the numbers for example 290 pascal for that boundary. What does it mean? How does the operating pressure affect the results? Thanks

 January 9, 2020, 03:55 #27 Senior Member   Join Date: Nov 2013 Posts: 1,965 Rep Power: 26 real pressure = operating pressure + gauge pressure. For Fluent "static pressure" means "gauge pressure".

 March 10, 2020, 00:37 Multiphase subcooled boiling #28 New Member   Atharv Join Date: Mar 2020 Posts: 2 Rep Power: 0 I am currently working on multiphase subcooled boiling.I am confused on including my inlet pressure.I think it is best to include it in operating conditions and then set both gauge pressure equal to zero as velocity inlet and pressure outlet conditions.However while doing so I came across reversed flow at outlet.what can be done under such circumstances. Inlet pressure:4.5e06 Outlet pressure:not known Inlet velocity:taken from fully developed flow

 March 10, 2020, 07:59 Operating pressure #29 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36 The operating pressure in an incompressible system is nothing but a way of reducing the round-off error. If the system is considered compressible, then it must be set to 0, so that Fluent starts working in absolute pressure instead of gauge pressure. Flow reversal is not much affected by the operating pressure value. This could be temporary thing, due to initial guess or it could be because there is certain obstruction near the outlet which is not parallel to the flow or it could be real. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 March 10, 2020, 09:27 Multiphase subcooled boiling #30 New Member   Atharv Join Date: Mar 2020 Posts: 2 Rep Power: 0 Is operating temperature not the basis for pressure drop calculation? Any drop shall be subtracted from same to display pressure contour?

 March 10, 2020, 09:35 Pressure-drop #31 Senior Member     Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 36 The drop in pressure is independent of operating pressure. It only depends on the locations across which drop needs to be determined. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

 April 15, 2024, 04:55 #32 New Member   Abdullah hassan Join Date: Oct 2023 Posts: 9 Rep Power: 2 Suppose i am working on shell and tube heat exchanger with the shell side performing condensation of ammonia steam. the working pressure at shell side will be 5.260 bar, and the tube side has only water with working pressure of 8.500 bar. How can i input my pressure values with mass flow inlet and pressure outlet boundary conditions?

 April 15, 2024, 05:06 #33 New Member   Abdullah hassan Join Date: Oct 2023 Posts: 9 Rep Power: 2 Suppose i am working on shell and tube heat exchanger with the shell side performing condensation of ammonia steam. the working pressure at shell side will be 5.260 bar, and the tube side has only water with working pressure of 8.500 bar. How can i input my pressure values with mass flow inlet and pressure outlet boundary conditions?

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