AFOSR droplet breakup project

We are investigating the role of cavitation in droplet dynamics following droplet-shock interactions and improve the prediction of this phenomenon. The research will enhance the prediction of rain loading on hypersonic vehicles by illuminating the role of cavitation in droplet breakup.

We are collaborating with Prof. Kinzel’s group at UCF to develop microscale models of the droplet using a volume of fluid approach to capture the internal droplet wave structure, time-accurate and nuclei dependent cavitation inception and Rayleigh-Plesset (RP) equation based bubble collapse. The new model will be validated against the experimental data.

Prof. Vasu’s group at UCF is conducting shock tube experiments for visualization and measurement of shock waves interacting with single and multiple droplets. Initial detonation tube measurements allowed the students to gain experience using a drop generator and performing basic drop-shock imaging. Migration to the shock-tube is underway. It is planned that acoustic levitation of droplets will assist in accurately focusing the visualization and measurement devices to precisely capture the interaction and breakup. Obstacles to levitation including the required low pressure in the shock-tube test section are being addressed.

Prof. Kinzel’s CFD simulation of shock interacting with pure water region (no nuclei).  Low pressure inside droplet due to internal shock reflection is shown.

Currently at BU direct numerical simulations of a bubble inside a raindrop are being developed. We are trying to capture the effect that when a bubble grows and it is near the droplet interface, it causes a perturbation on the droplet surface.  Additionally, when a bubble collapses near a free surface, it will do so asymmetrically due to an imbalance of liquid pressure.  One side of the bubble will accelerate faster than the other, and a jet forms pointing away from the nearby surface.  Because the jet has such a high velocity, it can impact the opposite side of the droplet and initiate another instability. Initial simulations with OpenFOAM show a bubble growing and collapsing near a free surface.  The free surface perturbation and jetting can be seen.  The red region is water and the blue region is air.