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Best way to calculate flowrate?

Posted Jan 9, 2011, 10:32 p.m. EST 5 Replies

Nathan Lane
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Hi all,

For fluid flow through a pipe I am currently calculating flowrate by integrating the component of velocity orthogonal to the inlet/outlet over the inlet/outlet surface. For my flow in z-direction my inlet flowrate (my inlet is orthogonal to the z-direction) is the surface integral of w (the z-component of velocity) over the inlet.

Is there an alternative way to calculate flowrate? Perhaps a default option for calculating flowrate when using the CFD module?

Cheers

5 Replies Last Post Jan 13, 2011, 2:03 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 10, 2011, 3:52 a.m. EST
Hi

not what I know about (but I do not say I know everything, particularly not in CFD) but what is wrong with integrating velocityover the inlet/outlet area ?

--
Good luck
Ivar
Hi not what I know about (but I do not say I know everything, particularly not in CFD) but what is wrong with integrating velocityover the inlet/outlet area ? -- Good luck Ivar
Nathan Lane
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Posted: 1 decade ago Jan 10, 2011, 10:17 a.m. EST
I was just wondering if this information was automatically created somewhere else in COMSOL, especially for flow through an open system. I have also run some more complicated geometries and noted slight (1-2%) differences in flow rate at inlet and outlet and wondered if that discrepancy was impacted by the accuracy of the surface integral.

Cheers, Nathan
I was just wondering if this information was automatically created somewhere else in COMSOL, especially for flow through an open system. I have also run some more complicated geometries and noted slight (1-2%) differences in flow rate at inlet and outlet and wondered if that discrepancy was impacted by the accuracy of the surface integral. Cheers, Nathan
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 11, 2011, 1:50 a.m. EST
Hi

flow rates , or in general any integration is done on the mesh ndoes with shpae function developments, so if you have a dense mesh you will get a more precise value. Anhow, for me FEM is 3-5% precise in most cases, to get < 1% you need a looot of RAM and tiiiime ;)

--
Good luck
Ivar
Hi flow rates , or in general any integration is done on the mesh ndoes with shpae function developments, so if you have a dense mesh you will get a more precise value. Anhow, for me FEM is 3-5% precise in most cases, to get < 1% you need a looot of RAM and tiiiime ;) -- Good luck Ivar
Nathan Lane
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Posted: 1 decade ago Jan 13, 2011, 1:18 p.m. EST
Just curious...

If you are running a CFD flow problem what is your preferred choice of solver/solver settings?

I have a little bit of RAM at my disposal (24GB) and have been using a direct solver (mostly because I had trouble with the default settings for the iterative solver the first time I used the CFD module).

Nathan
Just curious... If you are running a CFD flow problem what is your preferred choice of solver/solver settings? I have a little bit of RAM at my disposal (24GB) and have been using a direct solver (mostly because I had trouble with the default settings for the iterative solver the first time I used the CFD module). Nathan
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 13, 2011, 2:03 p.m. EST
Hi

I usually use the default values in my patched 4.1.0.112

--
Good luck
Ivar
Hi I usually use the default values in my patched 4.1.0.112 -- Good luck Ivar

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