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Difference MassFlow Function, AreaInt and AreaIntAbs

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Old   March 17, 2011, 05:09
Default Difference MassFlow Function, AreaInt and AreaIntAbs
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Hello

I have got problems with understanding the difference between the following Functions

MassFlow = -rho*V*n
with V as velocity vector and n as normal vector.

On the other side i defined the following function
Int = areaInt(Density * Velocity in Stn Frame w)@Interface

And Also this function
Intabsolut = areaInt(Density * abs(Velocity in Stn Frame w))@Interface

The results are the following:
MassFlow = 0,01120 -> positiv means here directed into domain
AreaInt = - 0,01062 -> negative means here directed into domain
AreaIntAbsolut = 0,05602

I do not really understand the connection of these values. Where comes the difference between MassFlow and the AreaInt. What is the relation between the AbsolutAreint, and so on. Could anyone of you help me out?

Thanks
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Old   March 18, 2011, 07:46
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Is the interface flat? In which plane? I assume it has a recirculation to give the negative flows.
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Old   March 18, 2011, 09:38
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Hi

Yes the Interface is flat and in the x-y plane and your assumtion is right. one part of fluid is getting through of the domain, and the other returns cause of the Geometry under the interface plane
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Old   March 21, 2011, 09:02
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PLZ! Need help!!!
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Old   March 21, 2011, 15:27
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What does the balance in the outfile say?
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Old   March 21, 2011, 15:30
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What are the exact expressions you used to calculate "MassFlow". You show V*n, but you would need to do V dot n.
In general look at the boundary flow data in the .out file to get the correct mass flow data, but you should be able to calculate something very close to this in Post.
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Old   March 22, 2011, 05:45
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Hi there

This is wat the Out File says
+--------------------------------------------------------------------+
| P-Mass-Fan |
+--------------------------------------------------------------------+
Domain Interface : Interface Zyl_Fan_Bottom (Side 2) 1.4351E-02
Domain Interface : Interface Zyl_Fan_Side (Side 2) -2.4885E-02
Domain Interface : Interface Zyl_Fan_Top (Side 2) 1.0534E-02
-----------
Domain Imbalance : 2.4521E-09

Domain Imbalance, in %: 0.0000 %

To calculate my massflowdata I used following definitions:

massFlow function (Function of Ansys itself) = - rho*V*n.

@Stumpy V is the Velocity, why should I use there Vdot - acceleration?! I don't get it? I think you mean Vdot as Volumefluw? The meaning of V here is the velocity. Am i right?

AreaInt = (Density * Velocity in Stn Frame w)@Interface
(depends on the outlet or inlet direction)

AbsAreInt = (Density * abs(Velocity in Stn Frame w)@Interface
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Old   March 22, 2011, 10:07
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Hi,
it's not Vdot (as in the derivative), it's the dot product of V and n, i.e -rho*V.n, but it looks like your interface normal is in the z direction everywhere, so it shouldn't matter.
I assume you were looking at the Fan_Top interface. The out file values seems to agree fairly well with the massFlow function and the Int expression. The Intabsolut expression is not going to give the correct net mass flow since it doesn't consider flow in and out. The values in the .out file are always the most accurate. I'm a little surprised Post isn't just reading these values from the res file when using the massFlow function, which would give identical values in Post and the .out file.
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