Problem with pressure outlet (Pgauge)
 

Dear all,

I am stuck in my simulations and I would really appreciate your help.
I am trying to model the flow discharge over an ogee spillway using VOF model. I know the mass flow rate/velocity at the inlet. I don’t know the flow features at the outlet.

The boundary conditions that I am using are:
-Velocity inlet (for air)
-Velocity inlet (for water)
-Symmetry (at the top of the computational domain)
-Pressure outlet (downstream of the comp. domain). I left Pgauge=0 (default).

I am obtaining a Pressure contour like the one I attached. The pressures are well computed in the overall domain (I compared with experimental data), except at the outlet section (see attach).
My doubt relates to the pressure drop existent at the outlet section (pressure drops to values close to 0). I am simulating a part of the spillway (the real spillway does not ends at my outlet section), so the flow is supposed to have continuum characteristics at the outlet, Therefore pressure should have a continuum pattern, instead of this drop. I tried changing the ,Pgauge, value but I got divergence.
Does anyone know how can I overcome this issue? Should I define some sort of UDF which updates the static pressure based on the pressure from the interior?

P.S. I tried using outflow BC but results were completely unphysical, with the water ”rising” at this section(see attach).

Thanks in advance to any suggestion!

:confused: