Unstable convergence plot at inlet and outlet

[prakhairnar96]

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.

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

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[tsite]

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:
   

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

   

Best regards,
Fillia

[prakhairnar96]

@tsite

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

[tsite]

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

[prakhairnar96]

Thank you Fillia, it was helpfull.

[prakhairnar96]

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.

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[prakhairnar96]

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?