Numerical investigation on reacting shock-bubble interaction using AMR method

Abstract

This thesis investigates the low and high Mach number limiting cases in the reacting shock-bubble interaction (RSBI) using a novel adaptive mesh refinement (AMR) combustion solver with comprehensive H2/O2 chemistry. The numerical results are compared with an experiment by Haehn et al. [88]. The Richtmyer-Meshkov instability (RMI) dominates the shock-bubble interaction, and the shock focusing in the heavy bubble induces ignition. This work helps to understand the reactive RMI phenomena and to propose new safety codes for gaseous combustion concerning complex shock systems. A new compressible combustion solver, Fire, is built on an open-source AMR framework. Particular AMR criteria suitable for combustion simulation are proposed for high efficiency. A wide range of benchmark tests is successfully surveyed for validation. By following the initial experimental setup [88] and adopting the axisymmetric assumption, this work successfully reproduces most of the flow features observed in the experiment both qualitatively and quantitatively, including the bubble morphology evolution and the corresponding chemiluminescence images. For the low Mach number case (M = 1.34), the flame is deflagration, and the fuel consumption rate is nonmonotonic because of unsteady flame propagation. The deflagration waves mildly decrease the total vorticity but promote mixing by around 37% because of the thermal effects. The mixing promotion is approximately 71% related to the diffusivity and 29% 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 deflagration at the beginning but is unstable and tends to transit to detonation as a consequence of the shock-flame interactions. Nevertheless, the deflagration-to-detonation transition fails, and the stable combustion mode is deflagration. For the high Mach number case (M = 2.83), in contrast, the combustion wave is detonation. The detonation wave is first ignited by early-stage shock converging which is neglected by previous numerical studies, then a second ignition occurs near the equator due to regular refraction. Non-monotonic fuel consumption rate due to re-equilibrium caused by shock reflection is reported. The detonation waves significantly influence the shock system and promote mixing by around 270%. Comparing with the low Mach number case, both deflagration and detonation affect the total vorticity mildly, but their influences on the negative vorticity are opposite.