Abstract
Two-dimensional and three-dimensional computational fluid dynamics studies of a spherical bubble impacted by a supersonic shock wave (Mach 1.25) have been performed to fully understand the complex process involved in shock–bubble interaction (SBI). The unsteady Reynolds-averaged Navier–Stokes computational approach with a coupled level set and volume of fluid method has been employed in the present study. The predicted velocities of refracted wave, transmitted wave, upstream interface, downstream interface, jet, and vortex ring agree very well with the relevant available experimental data. The predicted non-dimensional bubble and vortex velocities are also in much better agreement with the experiment data than values computed from a simple model of shock-induced Rayleigh–Taylor instability (the Richtmyer–Meshkov instability). Comprehensive flow visualization has been presented and analyzed to elucidate the SBI process from the beginning of bubble compression (continuous reflection and refraction of the acoustic wave fronts as well as the location of the incident, refracted and transmitted waves at the bubble compression stage) up to the formation of vortex rings as well as the production and distribution of vorticity. Furthermore, it is demonstrated that turbulence is generated with some small flow structures formed and more intensive mixing, i.e., turbulent mixing of helium with air starts to develop at the later stage of SBI.
Highlights
The flow field created by shock interaction with a geometrically distinct density inhomogeneity entails the intense coupling of various types of fluid dynamic phenomena, such as shock wave refraction and reflection, generation and transport of vorticity, as well as turbulence mixing
Two other more accurate numerical approaches for simulating turbulent flows have not been selected in the present study mainly because that turbulence is generated only at the later stage of shock–bubble interaction (SBI) and the flow consists of mainly unsteady large scale flow structures that Unsteady Reynolds-Averaged Navier–Stokes (URANS) can capture very well at a much lower computational cost
Both 2D and 3D simulations have been carried out and it is demonstrated that the 3D predictions are much closer to the measured values, with a very good agreement between the predicted velocities of refracted wave, transmitted wave, upstream interface, downstream interface, jet, vortex ring, and the corresponding measured values
Summary
The flow field created by shock interaction with a geometrically distinct density inhomogeneity entails the intense coupling of various types of fluid dynamic phenomena, such as shock wave refraction and reflection, generation and transport of vorticity, as well as turbulence mixing. There have been many numerical/theoretical studies carried out to study SBIs. Picone and Boris presented a new theoretical model that showed that after a shock passed a bubble, the formation of vortex structures and continual distortion of the bubble were due to the generation of long-lived vorticity at the edge of the discrete inhomogeneity. Picone and Boris presented a new theoretical model that showed that after a shock passed a bubble, the formation of vortex structures and continual distortion of the bubble were due to the generation of long-lived vorticity at the edge of the discrete inhomogeneity They carried out a 2D numerical study on the interaction of a weak shock with a bubble to verify their theoretical model, and the simulated results were similar to those observed in the experiments of Haas and Sturtevant..
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