Unreliable results for water flow in thin pipe

[kevinreshower]

Hi,

I’ve been trying to simulate water flow through a thin pipe.
An initial attempt worked well and I got a result that was in line with what I was expecting.
first attempt

Then I slightly changed the shape and the results became very weird, the speed was 20 times as high and I don’t understand the reason for that
second attempt

I don’t understand what I’m doing wrong and would appreciate any input!
Also, isn’t it necessary for turbulent flow to know how rough the surface of the pipe is?

Thanks and best wishes,
Kevin

[kevinreshower]

Hi,

sorry, I just saw that the question was already answered 5 days ago.

Converged, But incorrect results

Hi @sgmkhan3! Have you tried running the simulation with velocity inlet and pressure outlet instead of pressure inlet & outlet? Usually if you set both boundary conditions as velocity or pressure the solver has problems converging. As far as I can see the last runs you did look good also in terms of convergence - which is not a guarantee that your simulation is correct (whatever correct means). Are you trying to validate experimental data of the Yamaha or is it a just-for-fun-simulation? Cheer…

My ultimate project contains 2 inlets and 1 outlet though and also fails to converge:
third attempt
What is the recommended approach with three openings

Cheers
Kevin

[jousefm]

Hi Kevin!

All runs finished fine - where do you see the problem? Only in the convergence plot for run 3? Do not put all your hope into convergence plots, they are a good indicator of how the simulation goes but no guarantee that the simulation will actually give you correct results or that they make sense physically.

Best,

Jousef

[kevinreshower]

Thank you Jousef, I’ll keep that in mind!