On the interaction between a diffraction shock wave and a cylindrical sulfur hexafluoride bubble

The evolution of a cylindrical sulfur hexafluoride (SF6) bubble in the flow accelerated by a nonuniform diffraction shock is investigated using a density-based compressible OpenFOAM solver. The diffraction shock is generated from an initial planar shock with a Mach number of 2.2 by a rectangular barrier, and the influence of the barrier height on the evolution of the gas bubble is analyzed in detail both qualitatively and quantitatively. The results show that with increasing barrier height, the diffraction shock becomes weaker and propagates more slowly, which alters the shape of the undisturbed zone inside the gas bubble. The undisturbed zone becomes more slender, and shock focusing occurs at a later time. The local high-pressure point formed by the intersection of transmitted shocks in the case of shock diffraction can enhance the pressure during shock focusing. In addition, the intensity of vortex pairs of the distorted gas bubble becomes weaker as the barrier height increases. In the case of the highest barrier, the propagation velocity of the vortex pair emerging behind the deformed incident shock is subsonic, in contrast to the supersonic velocity found for other barrier heights. In addition, although the barrier heights considered here increase evenly in sequence, the degree of reduction of the local Mach number behind the deformed incident shock becomes larger.