boundary condition options
 

I am trying to model a tank that has an influent and two outlets.

I used the tutorials for settlingFoam as my basis.

One outlet I specify as a fixed, uniform, velocity.
The second has the boundary condition pressureInletOutletVelocity, which the documentation states as "Combination of pressureInletVelocity and inletOutlet." I used this as this was used in one of the two tutorials. The other tutorial specifies uniform velocity values at all outlets - when I tried this my case rapidly crashed, possibly because small errors with all outflows fixed accumulating as unresolved mass errors - the diagnostics I saw did not provide much information on the cause, and since I can run for long periods with one outlet set up as pressureInletOutletVelocity I have not pursued this much.

However, reading the documentation, is this appropriate for an outlet? I am puzzled as to why it seems to be based on 'inletOutlet', and what the difference is between that and 'outletInlet.'

I set the volumetric flow through outlet #1 to be less than that entering through the inlet, and want the difference to leave through outlet #2.

When I run it I get the settled solids appearing to vanish periodically in the simulation. I did wonder if using 'pressureInletOutletVelocity' was creating a large outflow (with a velocity equal to that specified for the inlet) when the pressure gradient would otherwise have resulted in flow into the tank, and this was then upsetting the stability of the solver.