Numerical simulations of the diffraction of planar detonations in H2−O2 mixtures

Abstract

The results of the direct numerical simulation of the lateral diffreaction of a detonation propagating in a primary layer of stoichiometric H2−O2 as it comes into contact with a secondary bounding layer of stoichiometric H2−O2 are presented. The Flux-Corrected Transport (FCT) algorithm and time step splitting were used in the simulation. The H2−O2 reaction was approximated using a two-step mechanism consisting of an induction period of duration τi followed by a heat-releasing reaction with constant reaction time τi. An empirical relation based on full H2−O2 kinetics was used for the induction time τi. The simulation was initiated with a plane detonation without transverse waves in the primary layer. The simulation showed that quenching as opposed to direct initiation occurs under these conditions. These results were validated by the excellent agreement with experimental framing photographs of the diffraction process when the two primary and secondary layers are separated by a collodium film thick enough to block the effect of the transverse waves. The results of the simulation were then used to describe the diffraction and quenching process in detail. Framing photographs are also shown for diffraction in the absence of a separating film. In this case, direct initiation does occur due to the propagation of transverse waves into the secondary bounding mixture. These results suggest that in the case of stoichiometric H2−O2 primary and secondary mixtures, transverse waves play an essential role in initiation of detonation in the secondary explosive.