Discrete element simulations on the damaged surface hydrodynamics of tungsten powders with inert Ar gas

Ejecta of micrometer-sized particles from a shocked damaged metal surface into a gas environment are widely observed in the engineering fields. Investigating the transport of ejecta particles in the converging geometries is a challenging scientific issue. Rousculp et al. [ "Damaged surface hydrodynamics (DSH) flash report, " Report No. LA-UR-15-22889, 2015] have studied the transport of shock-launched tungsten powders from a cylindrical metal surface into an inert gas. In the so-called damaged surface hydrodynamic experiments, the effect of gas species on powder transport was investigated. Distinctive phenomena were observed in all cases in which particles aggregated into radial spikes or stripes with an azimuthal modulation of n > 20, though the initial powder coating was highly controlled and the shock loading was believed to be azimuthally uniform. In this work, discrete element method coupling with magneto-hydrodynamic simulations was employed to explore the mechanism behind the experimental phenomena. Results showed that stripes may be originated from the non-uniform initial distribution and small velocity difference of particles. The intense particle collision during the shock launching caused the microstripe-like structures, which merged into macroscopic ones observed in the subsequent particle transport process. Lagrange tracking revealed the stripes at different moments consisted of different particles. Oblique collisions played an important role in the long-term transport of ejecta particles in the convergence geometries, while the drag force of gas showed little influence. This work will promote the understanding of dense particle-gas flow in converging geometries.