Annular jets-I Fluid dynamics

Annular jets of water have been observed qualitatively and quantitatively. The jet behaviour has been found to depend primarily on the Weber number of the liquid sheet leaving the orifice.When the Weber number exceeds unity long thin jets are obtained; when it is less than unity, the jets take up a rounded form. At the transition point (W0 = 1) a discontinuity appears in the liquid sheet. A slight increase in Weber number from unity gives a perfectly cylindrical jet, the pressure inside being simply related to the liquid surface tension and the mean radius of the orifice.Jet lengths have been measured at high liquid flows (W > 1) and the results compare well with theoretical predictions, provided the orifice is clean. An approximate and simplified equation for the jet profile has been derived, but its validity is limited to long jets with high velocities.