LES of hydrogen-air deflagrations in a 78.5-m tunnel

A large eddy simulation (LES) model of gaseous deflagration, previously validated against the largest known 20-m diameter deflagration in the open atmosphere, is applied in this study to reproduce experimental data on uniform 20% and 30% hydrogen-air mixture explosions in a 78.5-m long tunnel. The model enables the transient modelling of deflagration dynamics with a laminar flamelet burning velocity which alters spatially and in time with mixture composition, pressure, and temperature. The turbulent burning velocity is computed using Yakhot's model of premixed turbulent combustion. Yakhot's transcendental equation is essentially customized to account for both the transitional phenomenon of turbulence generated by the flame front itself, and the fractal structure of the flame surface on an unresolved sub-grid scale (SGS) level. The LES model reproduced available experimental data for both 20% and 30% hydrogen-air mixtures in an unobstructed and an obstructed tunnel. The simulations gave insight into the dynamics of flame propagation and the pressure build up within and outside of the tunnel. The LES model enabled the analysis of phenomena that were not reported in the experimental study. For example, a significant increase in the maximum explosion overpressure was observed in the vicinity of obstacles due to obstacle side-on pressure wave reflection in later stages of the event.