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MassFlowAve vs. AreaAve (again, sorry)

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Old   November 11, 2009, 12:10
Default MassFlowAve vs. AreaAve (again, sorry)
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Hello,

I found plenty of search results explaining the difference between massflowAve and areaAve but I still can't get my head around why these functions give me different velocity averages at a pipe inlet with incompressible flow.
If, for velocity, massflowAve = Σ(ρAV)V/ Σ(ρAV)
and areaAve= ΣAV/ ΣA
why do these give different values when ρ is constant?
Feel like I've missed something really obvious here so apologies if it's a stupid question!

Thanks
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Old   November 19, 2009, 03:21
Default approximate results through surface integrals
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I noticed the same thing (in Fluent 6.3.26) and asked Fluent about this. Their response was that they were aware that the surface integral utility produces approximate results and that the right values (at least for some properties) can be obtained through the flux report. I have to admit that this has somewhat improved in Fluent 12, but the result of the integral is still heavily mesh dependent.
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