Simulation on jet formation induced by interaction of shock wave with SF₆ bubble

To better understand the mechanisms governing the shock focusing and jet formation, we simulated the interaction between the planar incident shock wave of the Mach number 1.23 and the SF₆ heavy gas bubble using the high resolution computation schemes and grid. The numerical results are consistent with the experimental results of the reference. It was found that the incident shock wave converges along the streamwise direction inside the gas bubble, and forms a pair of longitudinally symmetrical high pressure regions, which then collide in the central symmetrical axis where the shock focusing is completed. The shock focusing forms a local region with high pressure and density, considerably larger than the initial pressure and density. Its peak pressure exceeds by far the normal atmospheric pressure, implying that the SF6 heavy gas bubble has a strong cumulative energy effect. Simultaneously, the shock focusing also induces vorticity variation near the downstream interface of the gas bubble, and the rotation of the vortex pair accelerates the jet formation and development. Hence, both the high pressure region and the vorticity distribution near the downstream gas interface promote the formation of the jet.