Evaluation of the dynamical characteristics of fluid flow caused by collapse of a non-spherical near-surface bubble

Abstract

The paper is devoted to numerical study of the influence of the initial shape of a vapor bubble on the surface impact of the water jet emerging due to the bubble collapse. This problem is relevant to spreading of high-temperature melt under a layer of subcooled water. The vapor bubbles formed on the melt-water interface, upon complete penetration in water, are condensing rapidly to produce high-velocity water micro-jets directed towards the melt. Impact of these jets causes upward melt splashing. Superposition of these processes forms a dynamic layer where melt is mixed with water; the presence of this premixed layer can be a pre-requisite for steam explosion. In this work, numerical modelling by the boundary element method is performed for the collapse of a bubble of an oblate spheroid. It is shown that the water jets generated in this process possess the impulse comparable to that generated by a collapsing spherical vapour bubble of the same volume. By the numerical simulations and subsequent estimates it is obtained that collapse of non-spherical bubbles near the melt-water interface produces melt splashes of the height of few centimetres, which is sufficient for the occurrence of steam explosions.