Effect of spatial distribution of mesoscale heterogeneities on the shock-to-detonation transition in liquid nitromethane

TL;DR

This study uses GPU-accelerated simulations to analyze how the spatial distribution of cavities in liquid nitromethane affects shock-to-detonation transition, revealing that heterogeneity arrangement significantly influences initiation times.

Contribution

It introduces a detailed computational approach to examine mesoscale heterogeneity effects on detonation, highlighting the impact of cavity distribution and clustering on initiation delay.

Findings

Random cavity distribution shortens detonation initiation time by 15-20%.

Clustering of cavities further reduces initiation time by about 10%.

Spatial heterogeneity significantly influences shock-to-detonation transition dynamics.

Abstract

The sensitizing effect of cavities in the form of microbubbles on the shock initiation of a homogeneous liquid explosive is studied computationally. While the presence of voids in an explosive has long been known to induce so-called hot spots that greatly accelerate the global reaction rate, the ability to computationally resolve the details of the interaction of the shock front with heterogeneities existing on the scale of the detonation reaction zone has only recently become feasible. In this study, the influence of the spatial distribution of air-filled cavities has been examined, enabled by the use of graphic processing unit (GPU) accelerated computations that can resolve shock initiation and detonation propagation through an explosive while fully resolving features at the mesoscale. Different spatial distributions of cavities are examined in two-dimensional simulations, including regular arrays of cavities, slightly perturbed arrays, random arrays (with varying minimum spacing being imposed on the cavities), and randomly distributed clusters of cavities. The presence of the cavities is able to reduce the time required to initiate detonation---for a given input shock strength---by greater than 50%, in agreement with previous experimental results. Randomly distributing the cavities results in a 15-20% decrease in detonation initiation time in comparison to a regular array of cavities. Clustering the cavities---as would occur in the case of agglomeration---results in an additional 10% decrease in detonation initiation time in comparison to random arrays. The effect of clustering is shown not to be a result of the clusters forming an effectively larger cavity, but rather due to interactions between clusters upon shock loading occurring on the microscale.