Thermal power generated greater than shaft power available in CFX

rafr894 · March 24, 2023, 03:30

I am trying to design an impeller that is required to do a certain amount of work on the fluid, and pass a required amount of mass flow.

ghorrocks · March 24, 2023, 05:42

Have you looked at all the normal sources of inaccuracy? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

rafr894 · March 24, 2023, 06:01

Not extensively, but around the region that I would assume is the source of the error.

ghorrocks · March 24, 2023, 06:04

If you have not checked your simulation for accuracy then your model could be massively inaccurate. There is no point in trying to understand the details of a simulation which is massively inaccurate.

Opaque · March 24, 2023, 15:30

When the results are not as expected, there are a few sources of errors:

1 - User pre-processing error -> Incorrect setup
2 - Discretization errors --> assume the solution is converged; otherwise, meaningless
3 - User post-processing error --> Incorrect evaluation of results
4 - User expectations from the model --> is it the correct model for the expectations?
5 - Always the possibility of software error.

Where do we start? 1->5 or 5->1 ?

March 24, 2023, 03:30	Thermal power generated greater than shaft power available in CFX	#1
rafr894 New Member KristianRanta Join Date: Oct 2016 Location: Sundsvall Posts: 25 Rep Power: 9	I am trying to design an impeller that is required to do a certain amount of work on the fluid, and pass a required amount of mass flow. Last edited by rafr894; March 26, 2023 at 09:32.

March 24, 2023, 05:42		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Have you looked at all the normal sources of inaccuracy? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F rafr894 likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 24, 2023, 06:01		#3
rafr894 New Member KristianRanta Join Date: Oct 2016 Location: Sundsvall Posts: 25 Rep Power: 9	Not extensively, but around the region that I would assume is the source of the error. Last edited by rafr894; March 26, 2023 at 09:34.

March 24, 2023, 06:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	If you have not checked your simulation for accuracy then your model could be massively inaccurate. There is no point in trying to understand the details of a simulation which is massively inaccurate. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 24, 2023, 15:30		#5
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	When the results are not as expected, there are a few sources of errors: 1 - User pre-processing error -> Incorrect setup 2 - Discretization errors --> assume the solution is converged; otherwise, meaningless 3 - User post-processing error --> Incorrect evaluation of results 4 - User expectations from the model --> is it the correct model for the expectations? 5 - Always the possibility of software error. Where do we start? 1->5 or 5->1 ? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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