ABSTRACT

Numerical simulation is performed on the flow behaviors of a largescale submerged air bubble uprising in the water column until its burst. The submerged air bubble starts rising from where the static water pressure is 2kpa beyond the atmosphere pressure and goes up to the static free surface. In the numerical scheme, the RANS equations for the incompressible fluid are used to account for the flow characteristics of the continuous liquid phase. The volume-of-fluid (VOF) method is used for the gas-liquid interface (GLI) tracking. Air compression effect of the submerged air bubble to the ambient water flow is taken into account by using the gas status condition. The compressed air pressure inside a bubble (APB) is imposed as a known value on the cells around GLI when solving the Poisson pressure equation. The modeled results show that (1) volume expansion of the bubble lasts throughout the rising process, with its volume increased to about 6.3 times of its origin before its burst; (2) as a consequence of the volume expansion, APB decreases straightly to the atmosphere pressure until burst; (3) the pieces of the water body of the burst bubble falls on the static free surface and reduce to regeneration of new small bubbles; (4) modeled results indicate that the present numerical model is capable of reasonably simulating the process of deformation, rising, and bursting of a large scale bubble, and even regeneration of new small bubbles.

INTRODUCTION

Phenomena of bubble movement are often encountered in many branches of engineering and technology. For instance, the breaking waves can produce large amount of air bubbles in the upper layer of the flow. This air cushion will greatly affect the magnitude of the wave load.

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