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-   -   a question about Massflow Calculation (http://www.cfd-online.com/Forums/openfoam/84414-question-about-massflow-calculation.html)

xck1986 January 28, 2011 09:18

a question about Massflow Calculation
 
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 13:47

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)


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