Hydrodynamic instability at impact interfaces and planetary implications

Impact-induced mixing between bolide and target is fundamental to the geochemical evolution of a growing planet, yet aside from local mixing due to jetting – associated with large angles of incidence between impacting surfaces – mixing during planetary impacts is poorly understood. Here we describe a dynamic instability of the surface between impacting materials, showing that a region of mixing grows between two media having even minimal initial topography. This additional cause of impact-induced mixing is related to Richtmyer-Meshkov instability (RMI), and results from pressure perturbations amplified by shock-wave refraction through the corrugated interface between impactor and target. However, unlike RMI, this new impact-induced instability appears even if the bodies are made of the same material. Hydrocode simulations illustrate the growth of this mixing zone for planetary impacts, and predict results suitable for experimental validation in the laboratory. This form of impact mixing may be relevant to the formation of stony-iron and other meteorites.

EFFECT OF RELAXATION PROCESSES ON THE SHOCK WAVE FOCUSING IN A GAS SUSPENSION CLOUD

In this paper, the interaction of a plane shock wave in air with a cylindrical region of a gas suspension and the effect of relaxation processes for various particle sizes on the refraction and focusing of the shock wave are studied. In the course of numerical modeling, the Euler approach is used to describe non-equilibrium motion of the gas and dispersed phases. A second order accuracy method in space and time is used. Verification of the method through test problems by comparing with exact solutions and calculations of other authors confirms a capability of detecting shock wave refraction effects and wave focusing with the appearance of peak profiles in a distribution of parameters. With an increase in particle sizes, the relaxation zones behind the shock wave and secondary waves, which propagate through a gas suspension cloud, have a significant impact on the shock wave refraction, focusing of transverse shock waves, and interface instability evolution. A focus point is shifted towards suspension cloud boundaries, while for sufficiently large particles, it moves beyond the boundaries (external focus mode). Thus, the reflection pressure of transverse waves and intensity of the instability at the interface reduce.