Large eddy simulation of premixed hydrogen-air combustion characteristics in closed space with different shrinkage rate

The study investigates the effect of tube shrinkage rate on the explosion characteristics of premixed hydrogen-air in a confined space using Large Eddy Simulation (LES). The wrinkle factor of the flame surface density model is dynamically modeled based on the Fureby and Muppala (FurebyM) model. The numerical results from this model can be better verified with previous experimental results. The results indicate that a lower shrinkage rate results in longer flame propagation time from the reducer region. The peak flame front velocities were 68.6 m/s, 83.6 m/s, 96.4 m/s, and 103.6 m/s for tube shrinkage rates of 0.25, 0.5, 0.75, and 1.0, respectively. There is also a negative correlation between explosion overpressure and varying shrinking rates. The split tulip flame forms at a shrinkage rate of 0.25. Analysis of the flame structure and velocity flow field suggests that this phenomenon may be related to the formation of multiple fish-tail vortex structures on the left side of the flame front. Moreover, the effect of different shrinkage rates on the flame structure and the velocity flow field before the propagation of the premixed flame to the reducer region is relatively insignificant for tube structures with different shrinkage rates. This study provides a theoretical basis for protection against confined space explosions with premixed hydrogenair mixtures.