Standing shock prevents propagation of sparks in supersonic explosive flows

Images of electrical sparks in shock tube experiments with supersonic outflows show how standing shocks regulate electrical breakdown. The resulting radio frequency emission could diagnose flow structure in other explosive events such as volcanic eruptions. 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.

Automated summary

The text discusses how sparks and standing shocks observed in shock tube experiments regulate electrical breakdown, and how radio frequency signatures emitted by volcanic eruptions can diagnose fluid dynamic and electrostatic conditions. Research shows that sparks are initiated in a rarefaction region and cut off at the shock, limiting their radio frequency emissions to a characteristic frequency range.