Influence of flame topology and Mach number on flame-shock interaction in a semi-closed channel

The interaction between a laminar flame and a shock is examined in a numerical set-up based on a centimetric shock tube. A mixture of hydrogen and air at an equivalence ratio of 0.8 is first ignited at the end of the tube which leads to the development of a glove finger or a tulip flame towards which a shock is then sent. Realistic mechanisms for the chemistry are employed along with an accurate description of the diffusion including the Soret effect. Gravitational effects are also taken into account. The wall temperature is fixed at 300 K, which may seem a very stringent condition, but is better justified than the adiabatic condition because the very short interaction time limits the heat transfer with the wall. The impact of the description of the geometry (1D, 2D, and 3D) on the apparition of a transition to detonation is studied for two values of the incident shock Mach number. Depending on this Mach number, two different types of DDT are observed: one related to shock focusing occurring close to the axis of symmetry of the tube and a second type occurring in the vicinity of the reactive boundary layer. Finally, it has been shown that a small degree of asymmetry of the flame prior to its interaction with the shock can promote DDT, whereas excessive asymmetry tends to inhibit it. Novelty and significance statement The novelty of this research lies in the representativeness of the simulations of flame/shock interaction in terms of chemistry and transport modelling as well as numerical setup. These simulations offer new perspectives on the intricate links between compression waves and combustion enhancement, either by spontaneous self-ignition or by flame acceleration. An original relationship between the asymmetry of the flame front and the occurrence of a transition to detonation is demonstrated. The research contributes to efforts to reliably predict scenarios such as the transition from low-speed combustion to high-speed detonation.