Three-dimensional micro-jetting dynamics in a stoichiometric H₂/Air detonation

In this study, the three-dimensional dynamics of the microscopic hypersonic fluid jetting (or micro-jetting) phenomenon arising from the triple-point collisions of detonation cellular structures are investigated. The key motivation for this study arises from the fact the hydrodynamic flow structures responsible for the birth of micro-jetting, such as the shocks at the triple points and the Counter-rotating Vortex Pair (CVP), are inherently three-dimensional and can morphologically exhibit differences against two-dimensional simulations. A single cellular cycle of a stoichiometric H₂/air channel detonation wave is hence isolated and studied using highly resolved three-dimensional Adaptive Mesh Refinement (AMR)-based simulations. To achieve highly resolved simulations in three dimensions and ensure that the jetting processes are captured sufficiently well while maintaining computational feasibility, the simulations are performed for a small domain spanning two detonation cell widths in the shock-attached frame of reference. Results reveal that the jetting strength in three-dimensions is higher compared to the corresponding two-dimensional counterpart, thanks to a higher vorticity production arising from the intersection of a greater number of planar three-dimensional transverse shocks (TS) compared to 2D (4 TS in 3D vs. 2 TS in 2D). The CVP in three-dimensions manifests as a closed vortex loop leading to a mushroom-shaped jet morphology at the instant when a nascent Mach stem is born during the course of a detonation cell cycle.