# Difference MassFlow Function, AreaInt and AreaIntAbs

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 March 17, 2011, 05:09 Difference MassFlow Function, AreaInt and AreaIntAbs #1 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 6 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 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,826 Rep Power: 85 Is the interface flat? In which plane? I assume it has a recirculation to give the negative flows.

 March 18, 2011, 09:38 #3 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 6 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

 March 21, 2011, 09:02 #4 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 6 PLZ! Need help!!!

 March 21, 2011, 15:27 #5 Senior Member   Join Date: Mar 2009 Location: Europe Posts: 168 Rep Power: 8 What does the balance in the outfile say? __________________ - - - - - ------------------------------------------------------------------------ Please do not forget: I am not paid for answering your questions. Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."

 March 21, 2011, 15:30 #6 Senior Member   Join Date: Apr 2009 Posts: 516 Rep Power: 12 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 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 6 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

 March 22, 2011, 10:07 #8 Senior Member   Join Date: Apr 2009 Posts: 516 Rep Power: 12 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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