Numerical investigation on reacting shock-bubble interaction at a low Mach limit

We investigate the deflagration combustion in the reacting shock-bubble interaction at M = 1.34 using a novel adaptive mesh refinement combustion solver with comprehensive H₂/O₂ chemistry. The numerical results are compared with an experiment by Haehn et al [1]. The Richtmyer-Meshkov instability dominates the shock-bubble interaction, and the shock focusing in the heavy bubble induces ignition. By following the initial experimental setup published by Haehn et al [1]. and adopting the axisymmetric assumption, we successfully reproduce most of the flow features observed in the experiment both qualitatively and quantitatively, including the bubble morphology evolution and the corresponding chemiluminescence images. The fuel consumption rate is nonmonotonic because of unsteady flame propagation, and it also depends on interfacial instabilities. The deflagration waves increase transverse bubble diameter, mildly decrease the total vorticity, and promote mixing by more than 150% because of the thermal effects. The mixing promotion is approximately 88% related to the diffusivity and 12% related to other mechanisms after ignition. A new shock focusing mechanism is observed due to the secondary refracted shock. During shock focusing, Mach reflection occurs and transits from the bifurcated type to the single type. This transition causes two ignitions: the first occurs in the spiral hot spot entrained by the jet vortex, and the second arises from the hot spot caused by the triple point collision. After the second ignition, the newborn flame is a deflagration at the beginning but is unstable and tends to transit to a detonation as a consequence of shock-flame interactions. Nevertheless, the deflagration-to-detonation transition fails, and the stable combustion mode is deflagration.