Computations of bubble formation and pulsations generated by impacting cylindrical water jets

The impact of a water jet onto a water surface can entrain air-bubbles whose pulsations provide acoustic sources. Such impacts can occur during the breaking of a wave, or on a smaller scale, when a raindrop strikes a puddle of water. A better understanding of this phenomenon can lead to improved characterizations of the ambient noise and acoustic detection algorithms. Liquid on liquid impacts correspond to a breakdown of classical hydrodynamic theory which assumes that the free surface remains smooth and topologically invariant. A computational model using a generalized theory of hydrodynamics designed to rigorously treat liquid collisions is described in this paper. Numerical simulations are compared to experiments of a liquid cylinder impacting a still-water surface The simulations provide details not only of the initial formation of the air-entrained bubble at the time of the cavity collapse, but also the subsequent pulsations of this bubble until it rises back to the free surface. Computed initial bubble sizes and natural frequencies are compared to the experimental results for different cylinder lengths.