Numerical and experimental study on the behavior of vortex rings generated by shock–bubble interaction

Abstract

In this study, three-dimensional numerical simulations and experiments of the interaction between a normal shock and bubbles generated by the repetitive energy depositions of a laser pulse in a Mach 1.92 flow was conducted. As a result of the shock–bubble interaction, a vortex ring, caused by a baroclinic effect, was generated. Owing to the self-induced velocity field, the advection velocity of the vortex rings decreased with increasing laser pulse energy. In the experiments, when interactions among the vortex rings became strong, separations in transverse directions between adjacent bubbles were induced. This was reproduced through numerical simulations by imposing an artificial disturbance in the initial positions of the bubbles, i.e., by 5% of the bubble diameter in a transversal direction. The asymmetric behaviors of a row of vortex rings were classified into three patterns based on the ratio of the distance between the vortex rings to the size of the vortex rings ( λ: inverse Strouhal number). In pattern 1, with λ >2.9, there was negligible interference between the vortex rings because the interval of the vortex rings was sufficiently large. In pattern 2, with λ = 0.97–1.2, separation in the vortex-ring rows appeared, and the separation angle increased as λ decreased. In pattern 3, with λ <0.62, the interference intensified, and the vortex rings collapsed, forming a turbulent flow behind the shock wave.