Shock-driven hydrodynamic instability induced by particle seeding

TL;DR

This paper experimentally investigates a shock-driven hydrodynamic instability in a gas with non-uniform droplet seeding, revealing vortex formation due to multiphase flow interactions caused by shock acceleration.

Contribution

It presents the first experimental observation of a multiphase shock-induced instability caused by particle seeding and details its physical mechanism.

Findings

Development of counter-rotating vortices after shock passage

Instability driven by relative motion between phases due to shock acceleration

Vortex formation depends on initial seeding concentration

Abstract

We report an experimental observation of an instability in gas of constant density (air) with an initial non-uniform seeding of small droplets that develops as a planar shock wave passes through the gas-droplet mix. The seeding non-uniformity is produced by vertical injection of a slow-moving jet of air pre-mixed with glycol droplets into the test section of a shock tube, with the plane of the shock parallel to the axis of the jet. After the shock passage, we observe development of two counter-rotating vortices in the plane normal to that axis. The physical mechanism of the instability we observe is peculiar to multiphase flow, where the shock acceleration causes the second (embedded) phase to move with respect to the embedding medium. With sufficient seeding concentration, this leads to entrainment of the embedding phase that acquires a relative velocity dependent on the initial seeding, resulting in vortex formation in the flow.