SimScale CAE Forum

Converged, But incorrect results


I am performing CFD on a formula student plenum (Air Intake) and my aim is to analyze the velocity and pressure at different section. I have put the pressure inlet as atmospheric pressure (101325pa) and the pressure outlet as 24000pa as this is engine vacuum pressure for the Yahama R6 YZF. At the moment i have placed 1 outlet to see how the flows into the 1st cylinder. Additionally,I am trying to see the pressure and velocity inside the plenum at different sections, However, after analyzing the results, they seem odd. My convergence plot has an unusual shape and I’m not sure if it’s because of that that I am getting results which seem to be wrong. Can someone check through it quickly and let me know if they identify any errors please, thank you.


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?



Unreliable results for water flow in thin pipe

i’ll give that a go! thank you. I did the simulation in steady-state flow however, I think I would need it in transient flow. I’m trying to simulate air flow to optimize the geometry of a formula student plenum, it will be fitted onto is a Yahama R6 YZF engine. With the result, I’d improve my design in terms of geometry. Also i would need to simulate the outlets opening and closing at different times, is that possible in Simscale?

Many Thanks,



Hi Saeed!

If you expect the flow to show transient behavior you can test it but keep in mind that it is expensive in terms of core hours! Regarding your questions about outlet openings I assume that you mean the inlet of the manifolds depending on the stroke you are in, correct? That would be possible and very interesting to see! What you have to do is to prepare a CSV file where one column is the time and the other column the pressure. Now you upload the CSV for the inlet boundary condition and set the end time in the simulation settings according to the end time of your table. The time step can be calculated with the CFL condition or you go by heart and set the adjustable time step to true and set a fixed CFL number (which usually is set to a default value and I would not touch it unless you have to).

Hope that clears things up a bit. Let me know if you have any questions - the PowerUser and I would be more than happy to help you out!