Dual hierarchical particle jetting in divergently shocked particle rings

We study experimentally the formation of a dual hierarchical jet structure in dry dense particle rings subjected to the radially divergent shock loadings. The internal perturbations initiated from the internal surface of particle ring grow quadratically in time and evolve into dozens of jets with rounded cusps regularly separated by fine radially aligned filaments. A large number of small external jets emerge from the external jet shortly after the acceleration of the external surface reduces to zero, and exhibit a “spike-bubble” combined structure. After an initial fast growth the overall pattern maintains a novel proportionate growth until the interaction between the internal and external instabilities. As the internal jets approach the external surface, the radial progress of the internal jets is progressively retarded, leading to a total inversion of the jetting pattern, in which it is the ligaments rather than the jet cusps that penetrate the external surface. Although the growth of the internal and external jets both resemble the turbulent mixing of Rayleigh-Taylor instability, the marked differences in the shape of pattern suggest distinct mechanisms underlying the onsets of respective jetting pattern.