Understanding explosions - From catastrophic accidents to creation of the universe

This paper focuses on two extremes of explosions: the general class of Type Ia supernova (SNIa), which are surprisingly uniform thermonuclear explosions of white dwarf stars, and a specific gasoline vapor-cloud explosion that occurred at the Buncefield fuel depot in 2005. In both cases, recurring questions are whether an initial spark or small, local ignition could result in a detonation, and if so, how could this happen? The broader question is: What is the origin of the deflagration-to-detonation transition (DDT) in confined, partially confined, and unconfined systems? The importance of DDT to SNIa is based on the use of these objects as cosmological “standard candles” that are used for measuring distances and curvature in the universe. The importance of DDT to Buncefield is related to design and operational safety of industrial plants and fuel storage facilities. Combinations of observations, specific laboratory experiments, and selected numerical simulations have given us information and some understanding of the DDT process and its likelihood. Numerical simulation both of large- and small-scale phenomena in these reactive flows were important ingredients in the studies. The invention and discovery of numerical algorithms, including (but not limited to) monotone methods, implicit large-eddy simulation, and adaptive mesh refinement, enabled these simulations certainly as much as the increase in computer speed and memory. Unresolved issues that arose in these studies include the nonequilibrium, non-Kolmogorov properties of the turbulence and turbulent fluctuations in these flows, how these prepare the system for transitions, and how to represent the chemical reactions and energy release in the high temperatures and pressures that are near and might signal a transition.