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bouyantBoussinesqSimpleFoam: specify mass flow in and out or use pressure bc

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Old   October 17, 2012, 01:49
Default bouyantBoussinesqSimpleFoam: specify mass flow in and out or use pressure bc
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Julien de Charentenay
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I am struggling with one aspect of buoyantBoussinesqSimpleFoam. The case I am trying to simple is reasonably simple: a room with one inlet, one outlet and some internal heat loads.

My initial thoughts were to use a velocity inlet for the inlet, and a pressure outlet for the outlet. When I run this scenario, the cumulative time-step continuity error keeps increasing, and when I look at the results in ParaView, the velocity at the outlet is too small (i.e the surface integral of the velocity at the inlet is larger by a factor of about 2 than the surface integral of the velocity at the outlet).

In regards to setup: p_rgh is set to buoyantPressure with a value of 0 for all surface except for the inlet (set to zeroGradient). p is set to calculate for all surfaces.

I tried to have a look at what others have done (on this forum and others) and found a couple of cases where the flow rate is specified at the inlet and outlet. The cases are: airConditionedRoom case and one generated by HVAC Gui for OpenFoam available on the extend project website (

My impression is that my setup does not work as the boundary conditions for the pressure equation are not adequate (over-constrained). I am not entirely satisfied by the flow rate option as it could lead to an accumulation (or deprivation) of mass - although openFoam does check it.

Any opinion?

Kind regards,
Julien de Charentenay
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