We study the effect of cavity collapse in non-ideal explosives as a means of
controlling their sensitivity. The aim is to understand the origin of localised
temperature peaks (hot spots) which play a key role at the early stages of
ignition. Thus we perform 2D and 3D numerical simulations of shock induced
gas-cavity collapse in nitromethane. Ignition is the result of a complex
interplay between fluid dynamics and exothermic chemical reaction. To
understand the relative contribution between these two processes we consider in
this first part of the work the evolution of the physical system in the absence
of chemical reactions. We employ a multi-phase mathematical formulation which
accounts for the large density difference across the gas-liquid interface
without generating spurious temperature peaks. The mathematical and physical
models are validated against experimental, analytic and numerical data.
Previous studies identified the impact of the upwind side of the cavity wall to
the downwind one as the main reason for the generation of a hot-spot outside of
the cavity; this is also observed in this work. However, it is apparent that
the topology of the temperature field is more complex than previously thought
and additional hot spots locations exist, arising from the generation of Mach
stems rather than jet impact. To explain the generation mechanisms and topology
of the hot spots we follow the complex wave patterns generated and identify the
temperature elevation or reduction generated by each wave. This allows to track
each hot spot back to its origins. We show that the highest hot spot
temperatures can be more than twice the post-incident shock temperature of the
neat material and can thus lead to ignition. By comparing the maximum
temperature observed in the domain in 2D and 3D simulations we show that 3D
calculations are necessary to avoid belated ignition times in reactive
scenarios