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Old   January 30, 2009, 10:59
Default Mass Flow Imbalance
  #1
Ed Mueller
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I am runing a CFX analysis on a fluid pump, and when I look at the results, everything seems to be in order.

However, when I compare massflow at inlet to massflow at outlet, the outlet massflow is exactly one-half that of the inlet (the inlet massflow is correct according to hand calcs).

When I check the massflow out of the impeller, it is the same as that at the inlet so something is happening in my fluid out domain where the massflow out of the fluid out domain is precisely half of the massflow into the fluid out domain.

Does anyone have any ideas on why this is? Does this mean my run is not converged? I found it odd that it is exactly half of my inlet mass flow (to about .00001 decimal places).
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Old   January 30, 2009, 11:45
Default Re: Mass Flow Imbalance
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Ed Mueller
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Update:

Looking at my out file, I see that domain imbalance for fluid in is 50%. Anyone have any ideas on why this might be?

+--------------------------------------------------------------------+ | Mass-Water at 25 C-fluid_in | +--------------------------------------------------------------------+ Boundary : inlet 1.2643E+02

Domain Interface : fin_to_impeller (Side 2) -6.4413E+01

Domain Interface : fin_to_wear_ring_gap (Side 1) 1.1992E+00

----------- Domain Imbalance : 6.3213E+01

Domain Imbalance, in %: 50.0000 %
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Old   January 30, 2009, 14:22
Default Re: Mass Flow Imbalance
  #3
CycLone
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Hi Ed,

Do you have a frame change with different pitches? What type of boundary conditions have you applied?

-CycLone
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Old   January 30, 2009, 14:30
Default Re: Mass Flow Imbalance
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Ed Mueller
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My BCs are velocity inlet and static pressure outlet. I have frozen rotor frame change, but there is no pitch. All surfaces at the domain interfaces are 1:1. I partitioned the model into 3 partitions, so maybe there was an error transferring data there?
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Old   January 30, 2009, 14:34
Default Re: Mass Flow Imbalance
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CycLone
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I would check the interfaces. CFX won't get the mass flow out by 50%, so I suspect something is set up wrong.

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Old   January 31, 2009, 07:20
Default Re: Mass Flow Imbalance
  #6
Nitin Dewangan
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if you check, CFX solver again. there has information, how mass imbalance calculated. just see that once. . the mass will be distribted around the boundary conditions, other than inlet and outlet.

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