Explosion dynamics and safety implications of hydrogen–air mixtures in complex underground structures

Hydrogen poses a potential explosion risk in underground storage and transportation systems, while the influence of complex geometrical configurations on explosion dynamics remains insufficiently understood. This study employs large-eddy simulation (LES) to investigate the explosion characteristics of hydrogen–air mixtures in four representative spatial configurations: linear, L-shaped, n-shaped, and Z-shaped channels. The results show that the flame propagation velocity and overpressure in the L-shaped, n-shaped, and Z-shaped structures exhibit a distinct double-peak pattern. The first peak is dominated by the early-stage flame self-acceleration, whereas the second peak is strongly influenced by locally intensified turbulence induced by geometric turning regions. The maximum overpressure and flame speed follow the order Z-shaped > n-shaped > L-shaped > linear. Among them, the Z-shaped configuration generates the strongest corner-induced vortical structures, producing a peak Karlovitz number of 30.32 and elevating the maximum overpressure and flame speed to 116.39 kPa and 331.21 m/s, respectively (compared with only 38.98 kPa and 103.09 m/s in the linear configuration). The findings clearly demonstrate that enhanced flame wrinkling and elevated local reaction rates—both governed by corner-generated vortices—constitute the primary mechanism responsible for intensified pressure buildup in complex geometries. These insights provide essential guidance for explosion-resistant design and risk assessment in underground structures.