I couldn't find anything useful, either, in years of searching.
The usual academic stuff about the vena contracta is not helpful.
Apparently whatever has been learned is too commercially valuable to reveal.
Since I no longer have any commercial interest in it, I'll reveal a little of what I have observed.
First, you get a stable cylindrical stream from a sharp-edged hole normal to the exit face. Chamfers and radii will make the stream wander. Some nozzles take advantage of this, by chamfering the exit face across a diameter of the hole, so the exit is no longer planar. This causes the exit stream to oscillate along the line where the normal and slanted faces intersect. It deviates only a few degrees, but a circular array of such holes has been in production for a while. There may be an associated patent, but I haven't found it.
Second, if your stable cylindrical stream hits a planar surface, it spreads into a nice clean fan. This is used in 'pinbar' nozzles where the stream hits the square cut end of a cylinder of roughly the same size as the stream, producing a planar sheet normal to the stream, interrupted by whatever supports the pin. It works as well if the planar impact surface is angled, too, except you don't get full circle coverage of the fan, which leaves at the same angle to the stream as the impact surface.
I haven't done much work with non-round holes, mostly because they're hard to manufacture intentionally. I think some 'air assisted' nozzles distort the liquid stream into a fan by impacting it with fast moving air.
Basically, effective water nozzles that work at easily achievable pressures do their magic by making the water hit 'something', and there is considerable variety in the somethings used.
I get the impression that things work differently at high pressures, like in fuel injectors, but I have no real experience there.
Mike Halloran
Pembroke Pines, FL, USA
