Experimental Study of the Breakup of a Free-Falling Turbulent Water Jet in Air

Abstract

An experimental study on the breakup of a turbulent round-water jet in still air with a nozzle Reynolds number of 145,600 and Weber number of 10,400 is reported. The visual structure of the falling water jet was recorded by a high-speed camera, and the characteristics of the falling jet were investigated. As the jet travelled from the nozzle, initial surface disturbances grew, and the lateral oscillation of the jet surface was amplified. The jet thickness initially increased and then decreased because of the combined effects of lateral turbulence fluctuation and gravitational acceleration. The amplitude of the surface disturbance grew in an exponential form. Based on the averaged transverse-water distribution, the water jet spreading rate was found to vary between 0.5 and 1.8%, and the decay of the jet water core had an average value of 0.7%. The onset of jet breakup was found at a distance of approximately 100 times of the nozzle diameter. A theoretical model was developed for predicting the onset of jet breakup by comparing the dynamic air pressure with the restraining surface tension pressure. The velocity of the water drops released after breakup was measured and found to be approximately 0.8 times of the local jet velocity.