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Old   March 1, 2010, 05:09
Default calcMassFlow problems
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Jérémy Bulle
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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
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Old   March 1, 2010, 10:20
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Originally Posted by Gearb0x View Post
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).
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Old   March 1, 2010, 13:37
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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 ...
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Old   March 2, 2010, 13:59
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Originally Posted by Gearb0x View Post
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?
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Old   March 2, 2010, 14:11
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Well I don't see where I could have go wrong ...
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Old   March 2, 2010, 15:47
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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
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Old   March 2, 2010, 16:41
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Oh I'll try this!

Thank you!
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Old   March 2, 2010, 17:00
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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 ... ?
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Old   March 3, 2010, 10:45
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Originally Posted by Gearb0x View Post
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")
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Old   March 23, 2010, 05:21
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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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