Experiments on the Flow of Swirling Water through a Pressure Nozzle and an Open Trumpet

Marked departures from inviscid flow were found when swirling water was discharged downwards under pressure through a Perspex conical nozzle. A boundary layer of forced vortex motion formed on the free surface of the air core, and in this region the loss of total head was large. These results were confirmed by measurements of the tangential and axial velocities close to the free surface. When the supply pressure was low and the swirl great, the axial velocity was reversed in the upper part of the nozzle close to the forced vortex. Similar effects were found in gravity flow through a vertical trumpet. Moreover, outside the forced vortex above the trumpet, the downward flow under some conditions was concentrated in cylindrical zones of small radial thickness.