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

#1 
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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 

March 18, 2011, 07:46 

#2 
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Glenn Horrocks
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Is the interface flat? In which plane? I assume it has a recirculation to give the negative flows.


March 18, 2011, 09:38 

#3 
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Hi
Yes the Interface is flat and in the xy 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 

March 21, 2011, 09:02 

#4 
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PLZ! Need help!!!


March 21, 2011, 15:27 

#5 
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What does the balance in the outfile say?
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March 21, 2011, 15:30 

#6 
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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. 

March 22, 2011, 05:45 

#7 
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Hi there
This is wat the Out File says ++  PMassFan  ++ Domain Interface : Interface Zyl_Fan_Bottom (Side 2) 1.4351E02 Domain Interface : Interface Zyl_Fan_Side (Side 2) 2.4885E02 Domain Interface : Interface Zyl_Fan_Top (Side 2) 1.0534E02  Domain Imbalance : 2.4521E09 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 

March 22, 2011, 10:07 

#8 
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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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