Channel Detonations with Different Aspect Ratios with Stochiometric Ethylene-Air

The propagation of detonations through premixed gases in confined channels is of relevance in a number of propulsion systems, including pulse and rotating detonation engines. Such detonations are characterized by cellular instabilities that may be sensitive to the confinement geometry. This study details the effect of geometric cross-section on detonation instabilities in three-dimensional channels through detailed numerical simulations. To resolve the detonation structure, adaptive mesh refinement and complex chemical kinetics are employed to simulate three-dimensional detonation with premixed ethylene-air reactants. Two rectangular channels, with aspect ratios of 5.33:1 and 1.33:1, and one circular channel are used to investigate the detonation instabilities and formation of triple-surfaces in response to the shape of the domain. The varying aspect ratios of the same geometric cross-sectional area are anticipated to affect the frequency of triple-surface reflections at the walls and collisions throughout the wavefront, with narrower cross-sections increasing the number of reflections in that direction. Randomized ignition kernels are used to break the geometry-based symmetry in cell formation. The steady state of the wave is observed after propagating over seven characteristic diameters. The wave shows a far larger number of triple-surfaces throughout the detonation than the number of disturbances introduced to the wave from the initial condition. The cellular structure for three-dimensional detonation is significantly more complex than that of two-dimensional detonation; the third dimension allows for another mode of energy to propagate, thereby increasing the number of collisions and triple-surface development as the detonation wave travels. The effect of channel length on cell structure is studied by investigating the results of a channel with five times the characteristic length of the previous rectangular channels, but with the same aspect ratio.