Standing shock prevents propagation of sparks in supersonic explosive flows

TL;DR

This study demonstrates that a standing shock in supersonic explosive flows confines sparks, affecting their radio emissions, and offers new methods for diagnosing explosive phenomena through imaging and simulations.

Contribution

The paper reveals how a standing shock prevents spark propagation in supersonic flows, linking fluid dynamics with electrostatic emissions, and introduces imaging and simulation techniques for analysis.

Findings

Sparks originate upstream of the standing shock.

Sparks are initiated in the rarefaction region and cut off at the shock.

Radio frequency emissions are limited to high-frequency components.

Abstract

Volcanic jet flows in explosive eruptions emit radio frequency signatures, indicative of their fluid dynamic and electrostatic conditions. The emissions originate from sparks supported by an electric field built up by the ejected charged volcanic particles. When shock-defined, low-pressure regions confine the sparks, the signatures may be limited to high-frequency content corresponding to the early components of the avalanche-streamer-leader hierarchy. Here, we image sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Fluid dynamic and kinetic simulations of the experiment demonstrate that the observed sparks originate upstream of the standing shock. The sparks are initiated in the rarefaction region, and cut off at the shock, which would limit their radio frequency emissions to a tell-tale high-frequency regime. We show that sparks transmit an impression of the explosive flow, and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena.