Investigation of Droplet Aerobreakup Using Non-Intrusive Diagnostics and Numerical Simulations

The interaction between a propagating shock wave with droplets forms a fundamental process occurring in several propulsion applications. The ensuing processes including droplet aero-breakup and vaporization for non-reacting fluids, as well as ignition and heat release for reacting fluid, are strongly influenced by the droplet-shock wave interaction. The underlying physics can be further influenced by the presence of nanoparticles in the fluids as is the case for energetic fuels. This study will consider the droplet-shock wave interaction for non-reacting fluids with and without nanoparticles. A shock wave generated into the ambient by a pressurized tube is impacted upon single droplets suspended using an acoustic levitator. The subsequent droplet breakup, and acceleration of the dispersed droplet mass is studied using high-speed imaging including a Schlieren-based approach. Tests are conducted for droplets with and without nanoparticles, and effects of varying shock speed and strength are evaluated by studying the breakup and acceleration processes. Measurement results are compared with numerical simulations of the breakup phenomena conducted using Ansys FLUENT. The simulations model the problem using both a 2- D planar approach and a 3-D periodic boundary approach and utilize the Volume-of-Fluid technique for interface capture. Measurements of droplet mass loss and centroid motion will be directly compared with simulation results. Overall, the study will provide insight into the complex multiphase physics involved in droplet-shock wave interaction processes. Further, this work forms a precursor for more detailed investigations of the shockdroplet interaction using non-intrusive diagnostics including particle image velocimetry and planar laser induced fluorescence.