[Kushal Puri]

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.

[pakk]

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.

[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 )

[pakk]

Why? Because Ansys chose to define it in such a way...

[LuckyTran]

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.

[flow_CH]

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

[pakk]

real pressure = operating pressure + gauge pressure.


For Fluent "static pressure" means "gauge pressure".

[Atharv]

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

[vinerm]

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.

[Atharv]

Is operating temperature not the basis for pressure drop calculation?
Any drop shall be subtracted from same to display pressure contour?

[vinerm]

The drop in pressure is independent of operating pressure. It only depends on the locations across which drop needs to be determined.

[Abdullah hassan]

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?

[Abdullah hassan]

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?