Breakup and Evaporation in Shock Driven Multiphase Mixing

The Shock Driven Multiphase Instability (SDMI) involves several phenomena that occur concurrently across overlapping length and time scales. At the larger scales, the problem involves turbulent mixing due to acceleration across pressure and density gradients, like the classic Richtmyer-Meshkov Instability; however, the inclusion of effects on larger droplet size results in longer equilibration times. The SDMI involves multiphase phenomena across many length scales, from the mesoscales (cloud-scale) to the microscale (droplet-scale). At the mesoscales, bulk droplet vaporization rates, the lag time of the liquid phase, pressure, and density gradient can be described. Contrary, isolating the problem at the microscale particle-scale mixing can be explained by the droplet breakup and evaporation phenomena at a high Weber number. The concurrent phenomena at these conditions are complex and poorly understood, warranting further research in numerous physical systems such as detonation-driven propulsion engines, liquid-vapor cloud explosions, and atmospheric hypersonic flight. 

 

In this regard, experimental techniques are utilized in a shock tube facility to investigate shock-driven multiphase mixing. A strong shock impulsively accelerates an interface consisting of acetone droplets and saturated nitrogen carrier gas. The droplet size distribution is characterized in-situ utilizing a PDPA and Shadowgraph. The interface and droplet cloud development are captured through an ensemble series of planar laser-induced fluorescence and mie-scattering imagery, capturing the vapor and liquid phases, respectively. These measurements allow characterization of the droplet breakup, survival times, and vapor production rates. Results of the experiments are compared to predictions of lag time and evaporation rate by empirical and analytical breakup theories to determine the validity of and improve models utilized in simulations efforts.