Learning Forum

[hhayati]

Hello,

I faced an strange issue with pressure drop in a laminar water flow in a pipe.

the case is as follows:

Pipe diameter: 9.525 mm

Pipe length: 686 mm

Re=1284

Inlet velocity: 0.117 m/s

Water density 998.2 kg/m3; viscosity 0.001 Pa.s

Model: Laminar

Flow direction: from bottom to top

Based on analytical solution, for the vertical pipe, the pressure drop should be about 7600 pa. but what Fluent gives me is 1.18 pa!!!! It seems not accounting elevation pressure! and It reports the same pressure drop for vertical and horizontal pipes!! which is not correct, right?

This is not the only case, I ran multiple laminar flow simulations (different inlet velocities), and Fluent gave me the same pressure drop for vertical and horizontal orientations!!!

Am I missing something?

I would appreciate if you could help me. @Rob @DrAmine

Best,

[Rob]

Did you turn on gravity? By default Fluent doesn't account for hydrostatic head, https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v212/en/flu_ug/flu_ug_sec_bc_pinlet.html%23flu_ug_sec_pinlet_hydrostatic should get you started and then follow the links.

[hhayati]

Yes, I did enable gravity.
You mean Fluent does not account for the vertical distance between two points if it wants to report static pressure? If so, does it do this only for laminar flow or for both laminar and turbulent flow?

[Rob]

It's not linked to the turbulence, it's a function of the solver. Hence following the links as you need to work with the operating density.