SimScale CAE Forum

Unstable convergence plot at inlet and outlet

  1. I am having a set up of impeller which is enclosed in an enclosure & in boundary condition I have specified velocity inlet and pressure outlet. an impeller is rotating at 2920 RPM I want to check the total pressure drop at the inlet and outlet.

2 after running my study if I check the convergence in the inlet and outlet. it seems that the beginning result is stable but in the end, suddenly it becomes unstable.

  1. I have checked with increasing time steps for a simulation run but still, I got the same plot

Project Link:

https://www.simscale.com/workbench/?pid=9125585017109748065&rru=caae2d79-860e-4174-9efe-fcd60012822b&ci=46d0a95f-e721-4f09-ad9e-6d112697cf45&ct=CONVERGENCE_PLOT&mt=SIMULATION_RESULT

Hi, this is Fillia, thank you for using the forum.

I have two suggestions:

  1. Toggle on the potential flow initialization option prior to the run:
    flow initialization

  2. If this still does not work, consider using a Mean instead of a Fixed pressure value on the outlet:

Best regards,
Fillia

Hi Fillia,

thank you for the response.
Can you please elaborate on point no. 2 (what is a fixed value and mean value).
and when should we consider fix/mean value

Have a look at the bottom of the page here: Pressure Inlet and Outlet | Boundary Conditions | SimScale :slight_smile:

Thank you Fillia, it was helpfull.

1 Like

Hi Fillia,

I ran 3 more studies as per your suggestion.

  1. Turning on potential flow initialization.
  2. Potential flow initialization + pressure outlet mean value.
  3. Only pressure outlet mean value.

But still i got same convergence in all of the cases at inlet and outlet.

Project link:

https://www.simscale.com/workbench/?pid=9125585017109748065&rru=fa071c62-5ef9-478e-856c-9d265e47afad&ci=f90d6a4d-b025-4283-9ada-0bc995a66017&ct=CONVERGENCE_PLOT&mt=SIMULATION_RESULT

I even tried increasing simulation time but still, I got the same unstable residual at the inlet and outlet face of my model.

I did check related training files available on the Simscale I did not found anything different in it.

Should I believe in this result with convergence plot like this?