Flow Not Evolving Correctly in 3D Geometry

[ob3mi]

Dear all,
I'm facing an issue with a 3D flow simulation. When I impose a parabolic velocity profile at the inlet and set a constant pressure at the outlet, the internal flow does not evolve properly along the main (axial) direction.
Could this be due to a missing pressure gradient enforcement, or perhaps a problem in how the boundary conditions are defined?

Any insights would be greatly appreciated.

[vl-dud]

Could you show the whole code?