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-   -   bouyantBoussinesqSimpleFoam: specify mass flow in and out or use pressure bc (http://www.cfd-online.com/Forums/openfoam/108189-bouyantboussinesqsimplefoam-specify-mass-flow-out-use-pressure-bc.html)

julien.decharentenay October 17, 2012 01:49

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

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: opencae.jp airConditionedRoom case and one generated by HVAC Gui for OpenFoam available on the extend project website (http://www.extend-project.de/user-forums/extend-groups/33-heating-ventilating-and-air-conditioning-hvac-group-forum/435-hvac-solver-with-buoyancy)

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


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