Standing Shock Regulates Sparks in Explosive Flows

Abstract:

Electrical discharges and explosive flows have long been associated with each other. Flowing dust particles originate charge through triboelectrification and separate based on inertia, resulting in strong electric fields supporting discharges. These discharges can cause explosions in dusty environments, especially those rich in carbon, such as coal mines and grain elevators. Recent observations of explosive events in nature [1] and decompression experiments [2] indicate that the extreme flows of explosions may alter the discharge process itself, creating conditions under which parts of the hierarchy of the discharge phenomena, such as leaders, could be suppressed. In the experiments, a shock tube ejects a flow of gas and particles into an expansion chamber. We imaged an illuminated plume from a decompression of argon and a small amount of diamond particles and performed compressible hydrodynamics simulations which provide insight into the conditions supporting the observed behavior. The discharges occur below the sharp boundary of a condensation cloud that agrees closely with the Mach disk shock shape and height in the simulation. This represents direct evidence that the discharges are sculpted by the outflow. The spatial and temporal scale of the discharges transmit an impression of the shock tube flow, a connection that could enable novel instrumentation to diagnose the currently inaccessible supersonic granular phenomena.

[1] Behnke, S. A., et al. (2018). J. Geophys. Res. Atmos., 123(8), 4157–4174.

[2] Méndez-Harper, J. S. et al. (2018). Geophys. Res. Lett., 45(14), 7226–7235.

LLNL-ABS-812878

This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.