Characteristics of external overpressure and flame evolution induced by hydrogen explosion venting

This study employs CFD techniques to investigate the hydrogen venting process in large-scale confined spaces, systematically examine external explosions at different concentrations, and its quantitative effects on overpressure distribution and flame evolution. The results show that there is no external explosion outside at φ ≤ 10%. When φ = 20%, outdoor overpressure is dominated by an external explosion wave. However, when φ ≥ 30%, outdoor pressures is dominated by the maximum overpressure wave generated by the superposition of the external explosion wave with the combustion wave. External explosions significantly prolong the duration of near-vent overpressure. The explosion location directly relates to the flame relief rate and the unburned gas cloud extent. For 20% ≤ φ ≤ 60%, the relief flame evolves from a “spoon”-shaped jet flame into an “ellipsoidal” fireball with a certain reverse rotation speed and keeps spreading forward. Fireball length and width first increase then decrease with concentration, while height increases continuously. Flame propagation speed profile along the direction of the vent shows a bimodal structure caused by the jet flame and the external explosion. The superposition of external explosions and combustion waves leads to complex distributions of overpressure hazard zones and high-temperature disasters. The radius of overpressure hazards increases with the rise in concentration. At φ = 30%, the hazardous radii of high-temperature disasters for personnel and buildings peak at 27 m and 17.5 m, respectively. The results are significant for preventing and mitigating the risk of hydrogen deflagration at hydrogen-related industrial sites.