Atwood number effects on the instability of a uniform interface driven by a perturbed shock wave

The evolution of a uniform interface subjected to a perturbed shock wave has been experimentally studied over a range of Atwood numbers 0.22≤A≤0.68 and Mach numbers 1.2≤M≤1.8 using a vertical shock tube. The perturbed shock wave is produced by diffracting a planar incident shock over a rigid cylinder. The wave patterns of the perturbed shock are captured by high-speed shadowgraphy, while the evolution of the shocked interface is captured by planar Mie scattering. Besides the formations of a cavity and two steps, an apparent counter-rotating vortex pair emerges on the shocked interface due to the baroclinic vorticity deposition, as both the Atwood number and Mach number increase. Quantitatively, it is interesting to note that the amplitude growth rate of the shocked interface decreases with increasing the Atwood number, which is fundamentally different from the results related to the classical RM instability. This notable feature is explained by the approximation of an oblique shock hitting a uniform interface. For weak shock, a suitable time scaling is employed to collapse experimental data irrespective of the Atwood number difference.