Gravity-driven multiphase instability*

Relatively recently, shock-driven multiphase instability (SDMI) was identified in multiphase flows and shown to have both similarities with and differences from Richtmyer-Meshkov instability (RMI). A multiphase analog of Rayleigh-Taylor instability was described in 2011 for a situation when air sparsely seeded with glycol droplets was placed above a volume of unseeded air, producing an unstably stratified average density distribution that was characterized by an effective Atwood number 0.03. In that case, the evolution of the instability was indistinguishable from single-phase RTI with the same Atwood number, as the presence of the droplets largely acted as an additional contribution to the mean density of the gaseous medium. Our recent experiments investigate a situation when the volume (and mass) fraction of the seeding particles in gas is considerably higher,  and the gravity-driven flow is dominated by the particle movement. In this case, we still observe an interfacial instability. We present data characterizing its morphology and growth rate, and discuss the relevant physics.