The impact and air entrainment process of liquid plunging jets

This article presents a three-dimensional unsteady numerical simulation of a turbulent liquid plunging jet impinging on a quiescent liquid pool. The focal point of the study is the initial impact, penetration, and the subsequent air entrainment process. The multiphase, volume of fluid model with the geo-reconstruct algorithm is used in combination with the Reynolds averaged k-epsilon turbulence model. The process of the initial impact of the jet on the free surface, the formation of an air cavity, and the subsequent break-down of the cavity into small bubbles are captured and analysed. These simulations show, clearly and in detail, the process of air carry under by the liquid jet. The air cavity caused by the initial jet impact deeply stretches under the pool surface until break-down due to the shear created by a toroidal 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 found to be equal to about half the jet velocity at impact in agreement with previous studies, and the predicted penetration depth shows good agreement with previous correlations.