Detonation Cellular Structure Research Articles

THE STRUCTURE OF DETONATION WAVES

Multidimensional time-dependent numerical simulations have been used to study the initiation, propagation, and extinction of detonations in gases and liquids. The simulations, which calculate the detailed behavior of the interacting shock waves and reaction zones forming the detonation wave, are used to study the evolution of the instability that leads to the cellular structure of detonations. The simulations consist of two-dimensional time-dependent solutions of the convection of mass density, momentum density and energy coupled to models for chemical energy release. The convective transport equations are solved by the Flux-Corrected Transport algorithm. The chemical reactions and energy release are usually modelled by the two-step induction parameter model. We conclude that the behavior of the multidimensional structure of a detonation depends on the differences of the thermodynamic properties in the inductiori zones behind the Mach stem and the incident shock. The formation of unreacted pockets behind the detonation front depends on the inclination of the transverse waves and the curvature of the shock fronts. Highly curved fronts may result in large pockets. The temperature dependence of the induction time is a major factor in the regularity of detonation structure. Detonation structure is affected by the energy release parameters. Instantaneous energy release leads to one-dimensional structures. Fast energy release results in less regular structures. Very slow energy release results in large pockets, highly curved fronts, and the detonation may die out. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987406

Numerical simulations of the cellular structure of detonations in liquid nitromethane—regularity of the cell structure

The detailed structure of planar detonation waves in liquid nitromethane was studied using time-dependent two-dimensional numerical simulations. The walls are assumed to confine heavily the liquid explosive and boundary layer effects are neglected. The solution thus simulates the detonation structure near the center of a wide channel. Chemical decomposition of nitromethane is described by a two-step model composed of an induction time followed by energy release. A simplified equation of state based on the Walsh and Christian technique for condensed phases and the BKW equation of state for gas phases us used. When mixtures of both phases are present, pressure and temperature equilibrium between them is assumed. The simulations show a cellular pattern traced by a system of triple points dividing the detonation front into sections. However, a substructure of weaker triple points also traces out a nonuniform pattern within the main pattern, resulting in an irregular cellular structure. A correlation exists between the regularity of the cellular pattern and both the curvature of the front and the change in induction zone thickness at the triple points. If the induction time is a stronger function of temperature, the weaker triple points disappear and a more regular structure is produced. When the structures are regular, the detonation front is more curved and there is a larger change in induction zone thickness at the triple points. However, the large change in induction zone thickness also leads to the formation of unburned pockets that eventually disturb the symmetry and uniformity of the structure. We conclude that the regularity of the cellular pattern is strongly influenced by the temperature-dependence of the induction time.

Cellular structure of detonation in nitromethane

Wave-trace records presented here are of detonations in nitromethane-acetone mixtures and are identical to traces found in gaseous detonations on carbon-soot-covered sidewalls. The method of obtaining records is described, and results are illustrated and compared with those available in existing literature. Having duplicated one of the most useful tools of experimental gasdynamics, we made a direct comparison between the processes taking place in liquid and in gascous detonable mixtures. Conclusions are that the processes in the two media are indeed similar, and that the structure of detonation in netromethane is cellular.

On the Construction and Comparison of Difference Schemes

On the Construction and Comparison of Difference Schemes