# calcMassFlow problems

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 March 1, 2010, 05:09 calcMassFlow problems #1 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 Hello, I'm trying to use the "calcMassFlow" utility but I have some questions : - Currently, he calculates the massflow every 50 timestep but my case only writes data every 500 timestep. How to change this for calcMassFlow so that it calculates the massflow every 500 timestep instead of 50? - The massflow is exactly 2 times the massflow fluent calculates for the same case (1.34 wheras it should be 0.67). I've made a third dimension of 1 meter because fluents uses a 3rd dimension of 1 meter to calculate its massflow. Where is my problem? Thanks a lot for the help

March 1, 2010, 10:20
#2
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Bernhard Gschaider
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Quote:
 Originally Posted by Gearb0x Hello, I'm trying to use the "calcMassFlow" utility but I have some questions : - Currently, he calculates the massflow every 50 timestep but my case only writes data every 500 timestep. How to change this for calcMassFlow so that it calculates the massflow every 500 timestep instead of 50? - The massflow is exactly 2 times the massflow fluent calculates for the same case (1.34 wheras it should be 0.67). I've made a third dimension of 1 meter because fluents uses a 3rd dimension of 1 meter to calculate its massflow. Where is my problem? Thanks a lot for the help
You're referring to this utility http://openfoamwiki.net/index.php/Contrib_calcMassFlow, right?
That utility can only work with written timesteps, so I'm a bit amazed that you get output more often
About the factor 2: you're not by any chance using an incompressible solver and the density of your fluid is 0.5? The other suspect is that in the dictionary you've got a scaleFactor 2 (because of reusing that from a symmetric case for instance).
Bernhard

 March 1, 2010, 13:37 #3 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 Yep that's this utility About the rho, I set it to 1.2 for air About the scale it's commented So I don't understand why I get such results ...

March 2, 2010, 13:59
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Bernhard Gschaider
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Quote:
 Originally Posted by Gearb0x Yep that's this utility About the rho, I set it to 1.2 for air About the scale it's commented So I don't understand why I get such results ...
You're 100% sure that the factor 2 is not a problem with the case setup?
Bernhard

 March 2, 2010, 14:11 #5 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 Well I don't see where I could have go wrong ...

March 2, 2010, 15:47
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Bernhard Gschaider
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Quote:
 Originally Posted by Gearb0x Well I don't see where I could have go wrong ...
Me neither (because I don't know the case). One thing you try is to use foamDataToFluent (see UserGuide) to get data into Fluent and check whether the you get the expected value or the calcMassFlow-value there Bernhard

 March 2, 2010, 16:41 #7 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 Oh I'll try this! Thank you!

 March 2, 2010, 17:00 #8 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 I tried this and I get 0 in fluent so this must be a problem in the conversion. I made "foamDataToFluent" and "foamMeshTofluent" then I select fluent3ddp and tried to do report-> fluxes -> massflow but that doesn't work ... Normaly it's a 2D case but apparently when I select 2ddp this doesn't work since openfoam works with 3D meshes and specific boundary conditions. Maybe it's because of that ... ?

March 3, 2010, 10:45
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Bernhard Gschaider
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Quote:
 Originally Posted by Gearb0x I tried this and I get 0 in fluent so this must be a problem in the conversion. I made "foamDataToFluent" and "foamMeshTofluent" then I select fluent3ddp and tried to do report-> fluxes -> massflow but that doesn't work ... Normaly it's a 2D case but apparently when I select 2ddp this doesn't work since openfoam works with 3D meshes and specific boundary conditions. Maybe it's because of that ... ?
It is a 2D-geometry? You should have said that in the first place. Is it possible that the cells in OF are 2m "thick"? In that case you must modify the scale-factor accordingly (2D-massflows will only be comparable to Fluent if the mesh is 1m "thick")
Bernhard

 March 23, 2010, 05:21 #10 Senior Member   Join Date: Nov 2009 Posts: 102 Rep Power: 9 Now that I've made my case 3D, I no more have any problem ... Something had to be wrong with the 2D case, yet I paid attention to the third dimension ...

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