Experiments on air entrainment produced by a circular free falling jet

The process of a circular free falling jet entering an idle pool was studied with the objective of determining a relation between the naturally occurring disturbances on the jet surface and air entrainment. To this end the instabilities of the free falling jet were characterized and compared with the bubble count distribution and an estimated amount of entrained air in the plume. Different jet lengths were considered. The aeration process was captured through image sequences. Individ- ual analysis of each disturbance in the jet surface was made. Our results show that both the bubble count and entrained air have a linear relation with the steepness of the jet disturbances. Moreover, the wave-jet ratio is introduced, which defines an entrainment condition for all the studied cases.