Single-Head Detonation in an Obstructed Channel
Abstract:
Recent experiments have revealed the propagation of a sustained single-head detonation through an obstructed channel. In this study, new experiments and analysis of the complex three-dimensional behaviour of such a single-headed wave in stoichiometric hydrogen-oxygen mixtures is presented. An optically accessible channel of square cross-section containing obstacles with BR = 0.5 area blockage was used in conjunction with soot-foils and dual-axis high-speed schlieren imaging to study the phenomenon over an initial pressure range of 17 kPa - 24 kPa. Detailed analysis of the wave reveals a transverse asymmetry generated by detonation diffraction whereby a transverse detonation propagates in a zig-zag fashion down the channel reflecting off opposite channel sidewalls. Analysis of the single triple-point trajectory reveals a detonation propagation velocity between 1.4VCJ - 0.5VCJ, with the transverse detonation propagating at a constant 0.9VCJ until reflection on the channel sidewall. The trajectory of the triple-point is undisturbed by the presence of obstacles. In the vicinity of the triple-point, flow analysis indicates prompt ignition (<1 μs induction time) of the gas mixture behind the Mach stem and transverse waves, confirming the presence of detention waves within the structure. The role of the obstacle in the propagation mechanism is to weaken the Mach stem detonation through diffraction to generate a separation in the shock and flame, through which the transverse detonation propagates.