Gas and particle motions in a rapidly decompressed flow

Explosion source parameters are investigated by conducting a series of experiments in which a densely packed particle bed at high pressure is rapidly decompressed, resulting in the production of a shock wave and bed expansion. The study is performed in a cylindrical (D = 4.1 cm) glass vertical shock tube with a densely packed (ρ = 61%) particle bed. The bed is comprised of spherical glass particles, with diameters ranging from 44 to 297 μm, and individual experiments containing a narrower range of particles. High speed pressure sensors are utilized to capture the speed and strength of the shock and expansion waves. High speed video recordings and particle image velocimetry (PIV) measurements are collected to examine vertical and radial velocities of both the particle and gas phases.

In addition to optically analyzing the front velocity of the rising particle bed, interaction between the particle and gas phases are investigated as the flow accelerates and the particle front becomes more dilute. Interstitial gas velocities are tracked separately from the gas velocity above the initial particle bed to elucidate dynamics at the bed and dependence of the gas flow on the packing structure of the particle bed. These experiments explore the depth to which interstitial gases react to the expansion wave relative to initiation of bed motion of the uppermost 44 to 297 μm particles, as both gas and particle rise velocities change with particle size and packing density. These findings can be used to better understand the evolution of early stages of volcanic explosions, potentially aiding in the interpretation of field data and prediction of flow dynamics within the vent of a volcano.

This work is supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science and Academic Alliance Program, under Contract No. DE-NA0002378.