Accuracy of fan calculation

Fouch · June 27, 2021, 15:36

Hi evrybody,

I am currently trying to calculate fan performance with openFoam.
My mesh seems to be Ok according checkMesh and residual not so bad.
The problem is that the pressure calculated is less of 20% compared to what I expect !

I use simpleFoam so I multiply the result of the pressure with the density.

I attach the main files.

Please tell me if you need more details !

Thank you in advance for your help.

piu58 · June 28, 2021, 01:31

Pressures and forces are rather hard to calculate with high accuracy. I think the reason is:
Pressure/Force results from energy loss in turbulences. The turbulence itself is not calculated but at least partly modelled. The models give good result according fluid stream, but are less accurate of the real energy loss and the pressures joined to it.

Fouch · June 28, 2021, 15:23

Thank you very much for your answer.

Some people working in my compagny confirmed that it's very difficult to get accurate value for this kind of very narrow fan.

I will try to improve the result anyway.

piu58 · June 29, 2021, 00:25

Sometimes it is useful connecting (calibrating) your results with experimental data, may be with a simpler design but the same physics. You may use the simulation only for calculating the (relative) changes while optimizing the geometry.

June 28, 2021, 01:31		#2
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	Pressures and forces are rather hard to calculate with high accuracy. I think the reason is: Pressure/Force results from energy loss in turbulences. The turbulence itself is not calculated but at least partly modelled. The models give good result according fluid stream, but are less accurate of the real energy loss and the pressures joined to it. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

June 29, 2021, 00:25		#4
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	Sometimes it is useful connecting (calibrating) your results with experimental data, may be with a simpler design but the same physics. You may use the simulation only for calculating the (relative) changes while optimizing the geometry. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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June 28, 2021, 15:23		#3
Fouch Member Join Date: Feb 2020 Posts: 79 Rep Power: 6	Thank you very much for your answer. Some people working in my compagny confirmed that it's very difficult to get accurate value for this kind of very narrow fan. I will try to improve the result anyway.