I am trying to understand a waterjet system for maneuvering boats from a physics perspective. (See Marine Holland Parts if you are interested.)
The system uses venturis in the nozzles. My question is WHY?
I imagine it has something to do with increasing the speed of the flow ejected from the nozzle to increase thrust. If so, why use a venturi which narrows and then opens up again rather than just a narrowing towards the exit? The speed of flow at the exit would be greater.