Numerical simulations of shocks encountering clumpy regions

TL;DR

This paper uses advanced numerical simulations to study how shocks interact with clumpy regions, revealing complex stages of shock evolution, turbulence generation, and cloud destruction relevant to astrophysical phenomena.

Contribution

First simulation incorporating a sub-grid turbulence model to analyze shock interactions with clumpy media, exploring effects on shock dynamics and cloud destruction.

Findings

Shock mass-loading reduces shock Mach number.

Turbulence accelerates cloud destruction.

Shock can degenerate into a wave under high mass-loading.

Abstract

We present numerical simulations of the adiabatic interaction of a shock with a clumpy region containing many individual clouds. Our work incorporates a sub-grid turbulence model which for the first time makes this investigation feasible. We vary the Mach number of the shock, the density contrast of the clouds, and the ratio of total cloud mass to inter-cloud mass within the clumpy region. Cloud material becomes incorporated into the flow. This "mass-loading" reduces the Mach number of the shock, and leads to the formation of a dense shell. In cases in which the mass-loading is sufficient the flow slows enough that the shock degenerates into a wave. The interaction evolves through up to four stages: initially the shock decelerates; then its speed is nearly constant; next the shock accelerates as it leaves the clumpy region; finally it moves at a constant speed close to its initial speed. Turbulence is generated in the post-shock flow as the shock sweeps through the clumpy region. Clouds exposed to turbulence can be destroyed more rapidly than a similar cloud in an "isolated" environment. The lifetime of a downstream cloud decreases with increasing cloud-to-intercloud mass ratio. We briefly discuss the significance of these results for starburst superwinds and galaxy evolution.