From Perturbation to Ejecta: An Exploration of Mixing Regimes in the Blast-Driven Instability using High-speed Experiments and Hydrocode Simulations.

The fluid mixing caused by variable-density instabilities is important in a wide variety of scenarios from ocean mixing and astrophysical phenomena to nuclear fusion techniques and atomic weapons. This thesis explores the mixing resulting from a specific instability known as the Blast-Driven Instability (BDI). A novel experimental platform was designed and built with the intention of studying the BDI for this thesis. Using high speed experimental techniques, the first fully time-resolved observations of the BDI are made. An understanding of the general dynamics caused by the BDI are established. Analytical models used successfully in the literature are also shown to need modifications in order to capture the BDI behavior. These observations are then used to test two common mixing models (RANS and LES) in a digital-twin simulation designed to precisely match the novel facility used in the high-speed experiments. Simulation results are analyzed against the data and reasons for their agreement, or lack thereof, are explored in detail. The RANS and LES simulation are shown to capture the BDI development to the 0th order, at the least. The LES simulations are also shown to be crucially dependent upon the characterization of initial conditions. The experimental data is used in conjunction with the simulation results to explore the BDI's sensitivity to two key governing parameters. How changes in the governing parameters create qualitative and quantitative changes in the BDI's behavior is explored extensively. Incident blast-wave strength is shown to change the hydrodynamic time scale, while changes in density difference cause much more non-linear effects. Finally, various scaling attempts are investigated in an attempt to decipher how the mixing induced by the BDI can be explicitly linked to the governing parameters.Ph.D