[Karim Yassin]

Hi
I hope you everyone is doing well. I am new in the ANSYS world and been trying to use CXF to simulate a centrifugal pump. In the research paper i am imitating, the BC were sat to mass flow rate at the inlet and static pressure at the outlet. My question is for a known mass flow rate at the inlet what should be the value of the outlet condition? and would it be different for different mass flow rates?
Thank you

[ghorrocks]

The value at the outlet should match whatever the physical component you are trying model runs at. Good practice is to set the outlet to zero pressure and use a reference pressure to get the absolute pressure you want.

[Karim Yassin]

Originally Posted by ghorrocks

The value at the outlet should match whatever the physical component you are trying model runs at.

the physical component in this case is the mass flowrate? if so, i should set a monitor point at the volute exit to check the mass flow rate?

Originally Posted by ghorrocks

Good practice is to set the outlet to zero pressure and use a reference pressure to get the absolute pressure you want.

i am running a case with 1 kg/s per passage at inlet and 0 static pressure at inlet, what should i set the value of the reference pressure to? and would it be fixed for other values of mass flow rate?

Thanks for your efforts!

[Gert-Jan]

Originally Posted by Karim Yassin

the physical component in this case is the mass flowrate? if so, i should set a monitor point at the volute exit to check the mass flow rate?

During the calculation, just monitor the imbalances and you should be safe if these are within 0.1.

Originally Posted by Karim Yassin

i am running a case with 1 kg/s per passage at inlet and 0 static pressure at inlet, what should i set the value of the reference pressure to? and would it be fixed for other values of mass flow rate?

Why not take the default values as provided by CFX?

[Karim Yassin]

Originally Posted by Gert-Jan

During the calculation, just monitor the imbalances and you should be safe if these are within 0.1.

sorry but does this mean to monitor the Momentum and Mass RMS graph?

Originally Posted by Gert-Jan

Why not take the default values as provided by CFX?

That is what i am doing right now and waiting on the results. In the case of centrifugal pump, when should i stop the run and extract results?

[Karim Yassin]

Thanks for the time you gave to read and reply to my post!
Following your advices, the case is running at the moment and i would like to share with you some graphs that arose few questions.
As you can see in the full domain picture there is the monitor point at the exit of the volute. The imbalances are under 0.1 as shown in the graph.
But! the pressure value at the monitor point is steady at the 0 value defined for the outlet B.C, does not sound right! Also the mass flow rate value at the monitor point is ZERO which makes no sense. I sat the inlet condition to 1 kg/s per passage.
what is the problem here?
Thanks again!Domain.png

pressure.png

imbalances.png

mass flow rate.png

chart.jpg

[Gert-Jan]

RMS means Residuals. Not Imbalances.

You plotted the mass flowss. In and out. There is going something out, but not in. So, by far there is no balance. There is a huge imbalance.
But these are massflows, not imbalances. For this, create a new plot in the solver manager, use your RMB and select Imbalances.




Regarding your question:"When should I stop my calculation?".
Please read the FAQ over and over. I think most of your questions are there: https://www.cfd-online.com/Wiki/Ansy...gence_criteria

[Karim Yassin]

i am solving periodic, so when i set the pitch angles in the interfaces between the inlet pipe to impeller and the impeller to volute, should i do it manual and set it 90 degrees on the impeller side and 360 on the other sides?