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 heavily confine 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 is 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 trace out a non-uniform 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 a more regular structure is produced. We conclude that the regularity of the cellular pattern is strongly influenced by the temperature-dependence of the induction time.