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building environment fluid flow help

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I am attempting to simulate the air flow in a cross section of an agricultural building. Air flow is driven by a static pressure difference between the inside and the outside of the building of 25pa.

2D problems are representations of infinite 3rd dimension extent by default. However, i wish to add mean flux in the third dimension which maintains the static pressure of the domain. The domain has a constant pressure inlet and the outlet needs to be through the domain's plane.

Is this something that would be implemented by modifying the fluid properties' equations? Or am i missing a way to do this the easy way? Thus far i have learned only how to manipulate the default settings in the model tree.

I have attached the nonworking symmetry case model for illustration purposes.

Im new at comsol so feel free to tell me that im doing something stupid...


1 Reply Last Post 8 dic 2010, 16:21 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 8 dic 2010, 16:21 GMT-5
Hi

well I had a quick look, first I do not see how you adjust your pressure, using 1[atm]-25 as material property perssure but -25[Pa] as an absolute initial pressure, I would rather propose to use the same value as for the material, then the usual question is the inlet prssure an abolute or a differential pressure (I would have to go back to the doc, I never remember and do not find easily back the info ;) You define it as a pressure drop, or ?

Then you have your key question: what about the outlet ?
As for a steady state analysis you will see the pressure rise and that's it. I do not believe it is possible to define a tird direction (Z) outlet for a 2D (x-y) problem, as by default COMSOL adds a depth of 1[m] along Z and isolation. so for me you need to define your outlet somewhere along X or Y.

Then if you go to turbulent flow, should you add also temperature and gravity, and use a transient solver study ?

What exactly are you looking for ?


--
Good luck
Ivar
Hi well I had a quick look, first I do not see how you adjust your pressure, using 1[atm]-25 as material property perssure but -25[Pa] as an absolute initial pressure, I would rather propose to use the same value as for the material, then the usual question is the inlet prssure an abolute or a differential pressure (I would have to go back to the doc, I never remember and do not find easily back the info ;) You define it as a pressure drop, or ? Then you have your key question: what about the outlet ? As for a steady state analysis you will see the pressure rise and that's it. I do not believe it is possible to define a tird direction (Z) outlet for a 2D (x-y) problem, as by default COMSOL adds a depth of 1[m] along Z and isolation. so for me you need to define your outlet somewhere along X or Y. Then if you go to turbulent flow, should you add also temperature and gravity, and use a transient solver study ? What exactly are you looking for ? -- Good luck Ivar

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