## Fluids

#### Absolute Pressure, Operating Pressure, Reference Pressure

• Aye Sandar Kyaw
Subscriber

Hello Everyone,

Currently, I am running the single-phase, non-cavitating incompressible flow in ANSYS Fluent.

Even though I set the different operating pressures in the operating conditions dialog box, and reference pressure in the reference values dialog box by calculating from the velocity inlet, the post-processing result for the static pressure is not changed.

The result that I would like to get is absolute pressure. What I understand for calculating the absolute pressure is

Absolute Pressure = Gauge Pressure + Operating Pressure.

If so, even though the gauge pressure values are not changed, the absolute pressure values are changed based on the operating pressure, right?

How can I make sure of getting the correct absolute pressure?

• SRP
Subscriber

Hi,

All pressures computed or reported by ANSYS FLUENT are gauge pressures.

Operating pressure is set in the operating condition which is constant. It is the gauge pressure that varies.

The reference values used in the computation of derived physical quantities and nondimensional coefficients. These reference values are used only for postprocessing.

Thank you

Saurabh

• Aye Sandar Kyaw
Subscriber

Hello, Saurabh, thanks for your comment.
I understand that all the pressures that ANSYS fluent give are gauge pressures.

Moreover, I also set the operating pressure in the operating condition but the problem is when I really want to calculate the absolute pressure based on the results that I obtained (which are gauge pressures), the results (absolute pressures) changed based on the operating pressure I set because even though changing operating pressure didn't change the results of gauge pressure.

In this condition, what should I do in order to calculate the absolute pressure?

Sorry if my question is not clear enough for you. But I am really urgent to solve for this.

• SRP
Subscriber

Hi,

Can you please elaborate or share results, how you calculate the absolute pressure?

Please share results showing variation of absolute pressure with  changed in operating condition?

Thank you

• Aye Sandar Kyaw
Subscriber

Hello, Saurabh

Actually, I just exported the static pressure (gauge pressure) from the pressure contour lines of post-processing. In order to get the absolute pressure, I sum it up using the equation that I mentioned. As I said before, changing the operating pressure does not change the gauge pressure result in my simulation.

For example, if the gauge pressure is 100 Pa and I set the operating pressure as 100000 Pa, then the absolute pressure becomes 100100 Pa according to the equation. However, if the operating pressure is set to 50000 Pa, because of not changing the gauge pressure of 100 Pa in my simulation, the absolute pressure becomes 50100 Pa. For that reason, I don't know if this is correct or not and I am confused and having difficulty finding absolute pressure.

I also knew that obtaining the absolute pressure in setup by using Results - Reports - Surface Integrals - Area Weighted Average - Absolute Pressure

However, that only gives the selected region. What I want to get is all the exported gauge pressure as absolute pressure.

If you have any idea about that, I welcome all the comments.

Thank you.