Rob
Ansys Employee

OK, so you have a known mass flow for the primary nozzle, a (probably atmospheric) secondary feed and an outlet at a different pressure.  That may then discharge into a larger vessel.  You will (should) know most of the data you need. 

I've modelled a few of these, and helped my PhD supervisor clean up after a few experimental mishaps. They're far more complex than people realise, and the throat dimensions and ratios are critical to good operation: same as in vortex amplifiers.