Onset of Air Entrainment by a smooth plunging jet under atmospheric pressure

Abstract

The onset of air entrainment by a smooth vertical liquid jet impacting a pool of the same liquid has been experimentally determined. The ranges of parameters covered complement those considered by Lin & Donnelly (1969). The influence of the jet curvature is clarified. A model based on the viscous stress acting on the interface proves to be in good agreement with the experiments in the limit of very viscous liquids. For less viscous liquids, the critical capillary number happens to be mainly controlled by the ratio of the dynamic viscosity of the air and of the liquid. Besides, the observed evolution of the critical capillary number agrees with the mechanism suggested by Eggers (2001) that is based on the cusp dynamic.