395 / 2019-02-28 17:19:59

Experimental study of the instability driven by a perturbed shock wave

Interface instability; Diffraction; Perturbed shock; Atwood number

全体主题 > Interface Instabilities at Extremes

The instability of a uniform interface driven by a perturbed shock wave is experimentally studied using a vertical shock tube. The uniform interfaces with three different initial Atwood numbers are formed membranelessly. The perturbed shock wave is generated by the diffraction of a planar shock over a rigid cylinder. The wave patterns of the perturbed shock are captured by high-speed shadowgraphy with high resolution while the evolution of the shocked interface is quantitatively characterized by planar Mie scattering.
In addition to the formations of a cavity and two steps, an apparent counter-rotating vortex pair emerges on the top of the shocked interface due to the baroclinic vorticity deposition, as both the Atwood number and Mach number increase. It is interesting to note that the amplitude growth rate of the shocked interface decreases with increasing the Atwood number for all the three Mach numbers, which is fundamentally different from the Atwood number effects in the classical Richtmyer-Meshkov (RM) instability. Two kinds of amplitude growth rates are calculated by Richtmyer’s impulsive model, but both exhibit apparent disagreement with the current experimental results. Moreover, it is believed that the diffusion effect inherent to the continuous interface is not responsible for the different characteristics between the RM instability and the instability driven by a perturbed shock.
Based on the approximate solution of an oblique shock hitting a uniform interface, we qualitatively interpreted the Atwood number effects in the interface instability driven by a perturbed shock. Furthermore, all the experimental amplitude data collapse onto a single straight line at low Mach number using the velocity jump of the shocked interface as a time scaling.