Simulating compressible gas bubbles with a smooth volume tracking 1-Fluid method

Abstract

The physical relevance of an improved front-capturing 1-Fluid method is investigated considering the behavior of either incompressible or compressible gas bubbles driven by buoyancy in a two-dimensional framework. Through the coupling of a VOF–PLIC technique and a smoothing function of adjustable thickness, the Smooth Volume of Fluid technique SVOF is intended to capture accurately strong interface distorsion with large density and viscosity contrasts between phases, combined with the front-capturing automatic treatment of interface rupture or reconnection. The fundamental idea lies in using the regular VOF–PLIC technique, while applying a smoothing procedure affecting both physical characteristics averaging and surface tension modeling. A thorough assessment procedure is achieved comparing the present method, front-tracking simulations and experiments from Bhaga and Weber that characterize the shape and velocity of single gas bubbles rising into liquid columns. A series of 200 SVOF simulations was necessary to provide a unique set of smoothing and averaging parameters available for any kind of bubble that is stable in an axisymmetric framework. The front-capturing strategy greatly eases the extension to gas injection applications as there is no micro-management required during interface coalescence or break-up, and no volume correction either. Finally the robustness of the 1-Fluid SVOF method is demonstrated in two-dimensions, in the case of compressible or incompressible gas injection into cold metal alloys where the density ratio between phases is greater than 3500.