Initial Impact of Liquid Jets and Entrainment of Air Bubbles: A Numerical Study

Abstract

This paper presents a three-dimensional unsteady numerical simulation of a turbulent plunging liquid jet without artificial surface disturbance impinging on a quiecent liquid pool. The focal point of the study is the initial impact and air entrainment process. The multiphase, Volume of Fluid Model is used in combination with the Reynolds Averaged k-ε turbulence model. The process of the initial impact of the jet on the free surface, the subsequent formation of an air cavity and the subsequent break-down of the cavity into small bubbles are captued and analyzed. These simulations show clearly and in detail the process of air carryunder by the liquid-liquid jet. The air cavity caused by the intial jet impact stretches deeply under the pool surface untill break down due to the shear created by a torroidal vortex. The predicted maximum height of the developing air cavity shows very good agreement with existing semi-empirical correlations from the literature and experiments. The velocity of the front of the air cavity is equal to about half the jet valocity at impact as shown by previous works and the predicted penetration depth shows acceptable agreement with previous correlations. The VOF model shows a strong capability of tracking the interface between two phases.