Abstract

Droplet breakup is a complex process involving interfacial instability and transport across a wide range of length and time scales. Fundamental studies of shock-droplet interaction provide valuable insight into the physical processes behind droplet breakup at high Weber and Reynolds numbers. Hypersonic vehicles encounter atmospheric droplets which can result in damage and disrupt vehicle aerodynamics. The vehicle bow shock helps to breakup and evaporate these droplets before impact, but predicting these processes is complicated by the highly unsteady conditions. Breakup occurs through Kevin-Helmholtz, Rayleigh-Taylor, and other hydrodynamic instabilities which evolve through temporally varying conditions. Droplet breakup reduces the equilibration time and accelerates evaporation rates. These effects challenge our current computational capabilities, as they require additional models, simulation methods, and experimental validation. The ability to predict these systems, though, is essential for high-speed aviation, and to enhancing our understanding of our universe.

This talk will explore the breakup for droplets at high Weber numbers (>1000). High-speed (>1MHz) shadowgraphy provides measurement of the droplet deformation rate, acceleration, and breakup onset timing under shock-driven conditions. Laser-induced fluorescence images show late-time droplet morphology and evaporation under detonation-driven conditions. The deformation rates, acceleration, breakup times, and child droplet lifetimes are compared with existing models and new models for unsteady breakup conditions. 

Biography

Jacob McFarland is an associate professor in the J. Mike Walker Department of Mechanical Engineering at Texas A&M University. He has worked with Lawrence Livermore, and Los Alamos National Laboratories, as well as with the Air Force Research Laboratory and Naval Research Laboratory on shock-driven multiphase flow modeling. He received an NSF CAREER award in 2019 for his work on shock-driven multiphase instabilities and a Young Investigator Award from the ONR in 2020 to study droplet breakup in multiphase detonations. His current research interests are in shock-driven multiphase mixing, droplet breakup, multiphase detonations, and ejecta reaction modeling.