On the shock-driven hydrodynamic instability in square and rectangular light gas bubbles: A comparative study from numerical simulations

Abstract

A comparative investigation of the hydrodynamic instability development on the shock-driven square and rectangular light gas bubbles is carried out numerically. In contrast to the square bubble, both horizontally and vertically aligned rectangular bubbles with different aspect ratios are taken into consideration, highlighting the impacts of aspect ratios on interface morphology, vorticity production, and bubble deformation. Two-dimensional compressible Euler equations for two-component gas flows are simulated with a high-order modal discontinuous Galerkin solver. The results show that the aspect ratio of rectangular bubbles has a considerable impact on the evolution of interface morphology in comparison with a square bubble. In horizontal-aligned rectangular bubbles, two secondary vortex rings connected to the primary vortex ring are produced by raising the aspect ratio. While in vertical-aligned rectangular bubbles, two re-entrant jets are seen close to the top and bottom boundaries of the upstream interface with increasing aspect ratio. The baroclinic vorticity generation affects the deformation of the bubble interface and accelerates the turbulent mixing. Notably, the complexity of the vorticity field keeps growing as the aspect ratio does in horizontal-aligned rectangular bubbles, and the trends are reversed in the vertical-aligned rectangular bubbles. Further, these aspect ratio effects also lead to the different mechanisms of the interface characteristics, including the upstream and downstream distances, width, and height. Finally, the temporal evolution of spatially integrated fields, including average vorticity, vorticity production terms, and enstrophy are analyzed in depth to investigate the impact of aspect ratio on the flow structure.