a question about Massflow Calculation

xck1986 · January 28, 2011, 08:18

Hi Foamusers,

I have use rhoSimpleFoam to simulate a valve. Now I have a question about the massflow calculation.

In openfoam WIKI I have found a function: http://openfoamwiki.net/index.php?ti...cts&oldid=9706

functions
(
massFlow
{
type patchMassFlow;
functionObjectLibs ( "libsimpleFunctionObjects.so" );
verbose true;
patches ( inlet outlet );
factor 19.7363;
}
);

What I am not clear is the factor 19.7363. For My case I have use factor=1.
But the massflow results I get is 30% smaller than the results simulated by another CFD software StarCCM+.
In OpenFOAM WIKI, it said:

factor A
factor with which the results should be multiplied before being written to disk/terminal. Used to account for symmetries etc (not used by all function objects) Depending on the type of the functionObject in this library these entries are used:

So can anyone tell me what means here account for symmetries?
For my model I have use half of the CAD valve model to run the simulation, so I have a symmetryplane. Do I need to set this factor bigger than 1?

Thanks a lot!

nimasam · January 29, 2011, 12:47

hi chenkai
let me describe my point with an example.
u have an axiymetric mesh (consider a tube, you choose a section of it) as ur cross section is a portion of the main cross section, ur mass will be a portion of mass flow too! so i guess im not sure at ALL! the factor equals (tube cross section/ chosen cross section)

January 28, 2011, 08:18	a question about Massflow Calculation	#1
xck1986 Member chenkai Join Date: May 2010 Location: munich Posts: 44 Rep Power: 15	Hi Foamusers, I have use rhoSimpleFoam to simulate a valve. Now I have a question about the massflow calculation. In openfoam WIKI I have found a function: http://openfoamwiki.net/index.php?ti...cts&oldid=9706 functions ( massFlow { type patchMassFlow; functionObjectLibs ( "libsimpleFunctionObjects.so" ); verbose true; patches ( inlet outlet ); factor 19.7363; } ); What I am not clear is the factor 19.7363. For My case I have use factor=1. But the massflow results I get is 30% smaller than the results simulated by another CFD software StarCCM+. In OpenFOAM WIKI, it said: factor A factor with which the results should be multiplied before being written to disk/terminal. Used to account for symmetries* etc (not used by all function objects)* Depending on the type of the functionObject in this library these entries are used: So can anyone tell me what means here account for symmetries? For my model I have use half of the CAD valve model to run the simulation, so I have a symmetryplane. Do I need to set this factor bigger than 1? Thanks a lot! Last edited by xck1986; January 29, 2011 at 14:19.

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January 29, 2011, 12:47		#2
nimasam Senior Member Nima Samkhaniani Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,266 Blog Entries: 1 Rep Power: 24	hi chenkai let me describe my point with an example. u have an axiymetric mesh (consider a tube, you choose a section of it) as ur cross section is a portion of the main cross section, ur mass will be a portion of mass flow too! so i guess im not sure at ALL! the factor equals (tube cross section/ chosen cross section)