A numerical investigation of flame acceleration and deflagration-to-detonation transition: Effects of the position and the delayed injection time of fluidic obstacles

Fluidic obstacles, employed as a form of turbulence generator, are often utilized to facilitate flame acceleration and deflagration-to-detonation transition (DDT). This paper conducts a detailed numerical study focusing on the position (L1) and the delayed injection time. The results indicate that reducing L1 leads to an earlier interaction between the flame and vortex structures, thus enhancing the initial flame acceleration effect. However, this also results in a reduction in the movement of vortex structures, which prevents the enhancement of turbulence intensity within the channel. Conversely, notwithstanding increasing L1 can improve the turbulence intensity within the channel, vortex structures fail to interact with the flame, which is unfavorable for the DDT process. Therefore, an optimal L1 exists which not only improves initial flame acceleration but also accommodates DDT. Furthermore, from a comprehensive perspective, the effectiveness of the delayed injection strategy is constrained by the range of L1. When L1 is small, the delayed injection strategy can enhance the time window for the flame–jet interaction, thereby improving turbulence and finally enhancing the DDT performance. However, as L1 increases, this improvement gradually diminishes and ultimately disappears. Regarding the DDT process, this study reveals that the distribution and strength of the wave structure in the channel, the size of the recirculation zone, the motion effect of the vortex structure, and various flow instability are the internal causes of DDT. The intensity of the pressure and velocity fields in the unburned zone ahead of the flame plays a crucial role in the DDT process.