Shape deformations and instabilities of single bubble rising in liquid metals

Abstract

In this study, a computational fluid dynamics simulation was used to study single bubble flow in liquid metal. Until now, bubble trajectory and shape [Mougin, G. and Magnaudet, J., “Path instability of a rising bubble,” Phys. Rev. Lett. 88, 014502 (2002)] stability problems in liquid metal have only been insufficiently analyzed in the literature. Because of the difficulty of such an experimental validation, no universal correlations on terminal velocity, shape aspect ratio, and drag force coefficient have been produced to date. The existing bubble shape parameter and terminal velocity correlations with dimensionless numbers are still debatable, mostly because experimental validation is very challenging. The objective of this study was to develop new correlations between bubble stability and bubble deformation in liquid metals. An in-house code, PSI-BOIL, has been used for the simulations. A single bubble rising in a quiescent liquid has been simulated for three different sets of materials (nitrogen+mercury, argon+GaInSn, and argon+steel). The obtained results suggest that shape instability phenomena take place in the bubble dynamics in liquid metals for Eötvös numbers >1.7. Small bubbles ( Eo < 1.7) maintain a stable ellipsoidal shape, while the shape and velocity of larger bubbles ( Eo > 1.7) tend to oscillate with bubbles rising via non-rectilinear trajectories. The inviscid approximation works well for bubbles in liquid metals. It has been confirmed that the dynamics and the shape of small bubbles ( Eo < 1.7) in liquid metals are only controlled by the Weber number.