Normally I would say no to this but I've had a bonkers idea:
Could you do this with a particle study?
If you set your gravity to go up your pipe (and pick a sensible value) you could then add particles in at the bottom (as modelled) so they fall up the pipe taking a fluid flow with them.
There would be some fiddling around working out sensible particle sizes and masses and also what gravity value you should use to get a sensible rate of rise. On the plus side once you had these details worked out you could reuse them for future studies.
Please note: I have not tried this and I don't know if it would work, the idea just popped into my head!
Davids idea sounds feasible indeed
That's a clever idea indeed. However, it's not going to work because in SOLIDWORKS Flow Simulation the Particle Study is purely a post-processing tool which you run after you have already solved the main flow. Thus the particles can never affect the flow. This is one of the limitations of particle studies.
Actually, I don't think this type of simulation can be done in SOLIDWORKS flow simulation.
Ahh well I did say it was a bonkers idea! After I posted I did wonder about the post processing element.