Fluid analysis, potential energy

tkor · April 20, 2023, 21:26

No change in total pressure due to positional energy can be confirmed.

Water flows through straight piping from a height of 1 meter.
The water is flowing in the direction of gravity.
The diameter does not change.
Pipe is frictionless.
Boundary conditions are inlet total pressure, outlet mass flow

At this time, I think that the total pressure at the outlet side will increase by the amount of the positional energy at the inlet according to Bernoulli's principle, but the total pressure does not increase as a result of the analysis.
I also tried changing the gravitational acceleration in various ways, but there is no change in the total pressure at the outlet

Is there a problem with the boundary conditions?
Please give me some advice.

LuckyTran · April 21, 2023, 13:54

Just like in Bernoulli's equation / the mechanical energy equation, pressure in Fluent doesn't contain the hydrostatic component. You need to add it or set the reference density to 0.

tkor · April 24, 2023, 03:11

Thanks for the advice. It is very helpful!!

If I want to take hydrostatic pressure into account, what do I need to add?
I have tried enabling gravity, but there is no change.
Also, what do you mean by setting the reference density to 0?

NickFL · April 24, 2023, 06:37

Hydrostatic pressure can easily be created and visualized with CFF. If you have gravity enabled, then it is taken into account already. It is just not post processed as part of the static pressure.

In the setup there are the reference values (look in the tree). One of the values is for density.

tkor · April 24, 2023, 22:48

Thanks for the advice !
I am a CFD newbie.

I changed the reference value in the settings. I changed the density to 0.
It looks like I can visualize hydrostatic pressure but I don't know how to operate it.
The fluent post-processing can display static, dynamic, and total pressure, but how do you check the hydrostatic pressure?

NickFL · April 25, 2023, 05:09

What do you mean by operate it? If you want to visualize just the hydrostatic pressure, then you can create a Custom-Field Function for this value. Then you can plot it or treat it like any other variable. There are probably several examples if you search in this forum.

April 20, 2023, 21:26	Fluid analysis, potential energy	#1
tkor New Member tkor Join Date: Apr 2023 Posts: 9 Rep Power: 3	No change in total pressure due to positional energy can be confirmed. Water flows through straight piping from a height of 1 meter. The water is flowing in the direction of gravity. The diameter does not change. Pipe is frictionless. Boundary conditions are inlet total pressure, outlet mass flow At this time, I think that the total pressure at the outlet side will increase by the amount of the positional energy at the inlet according to Bernoulli's principle, but the total pressure does not increase as a result of the analysis. I also tried changing the gravitational acceleration in various ways, but there is no change in the total pressure at the outlet Is there a problem with the boundary conditions? Please give me some advice.

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April 21, 2023, 13:54		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Just like in Bernoulli's equation / the mechanical energy equation, pressure in Fluent doesn't contain the hydrostatic component. You need to add it or set the reference density to 0.

April 24, 2023, 03:11		#3
tkor New Member tkor Join Date: Apr 2023 Posts: 9 Rep Power: 3	Thanks for the advice. It is very helpful!! If I want to take hydrostatic pressure into account, what do I need to add? I have tried enabling gravity, but there is no change. Also, what do you mean by setting the reference density to 0?

April 24, 2023, 06:37		#4
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	Hydrostatic pressure can easily be created and visualized with CFF. If you have gravity enabled, then it is taken into account already. It is just not post processed as part of the static pressure. In the setup there are the reference values (look in the tree). One of the values is for density.

April 24, 2023, 22:48		#5
tkor New Member tkor Join Date: Apr 2023 Posts: 9 Rep Power: 3	Thanks for the advice ! I am a CFD newbie. I changed the reference value in the settings. I changed the density to 0. It looks like I can visualize hydrostatic pressure but I don't know how to operate it. The fluent post-processing can display static, dynamic, and total pressure, but how do you check the hydrostatic pressure?

April 25, 2023, 05:09		#6
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	What do you mean by operate it? If you want to visualize just the hydrostatic pressure, then you can create a Custom-Field Function for this value. Then you can plot it or treat it like any other variable. There are probably several examples if you search in this forum.