[Overdue]

Hey Guys,

I have some problems to understand the behaviour of a simple flow simulation in a pipe with pressure boundaries (total or static). For example: water flows through a straight pipe with a length of 1m and a diameter of 50mm.
To get a velocity of 1m/s, I can calculate the necessary pressure difference:

delta_p= rho/2*v² = 997 kg/m³/2 * 1 m/s = 498,5 Pa, that’s easy.


For my first simulation I choose the following boundaries:

• Inlet: total pressure = 498,5 Pa
• Outlet: Average static pressure, relative pressure = 0 Pa
• The remaining surface as a free slip wall

The result is correct, the velocity is about 1 m/s



And here is my problem of understanding in a second simulation:
When I choose static pressure instead of total pressure as my Inlet boundary, the result is completely different. The velocity is approx. 5,29 m/s. The min. and max. total pressure are 13939,5 Pa and 14449,1 Pa.


Can anyone explain how velocity and total pressure are calculated in this case?

Thanks in advance!

Best regards,
Luke