Numerical simulation of overpressure loads generated by gas explosions in utility tunnels

Studies of overpressure loads are essential to mitigate the potential hazards of public safety induced by gas explosion accidents. Based on the computational fluid dynamics (CFD) code FLACS, numerical models of gas explosions in large-scale tunnels were developed and verified by comparing with testing data. Numerical simulations of gas explosions in confined and side-vented utility tunnels were carried out. The effects of the venting condition, gas cloud volume, and ignition position were analyzed and discussed. It is found that gas explosions in utility tunnels can be divided into three stages according to the pressure and flame development, i.e., the combustion-induced rise stage, oscillation rise stage, and oscillation decline stage. The pressure oscillation is significant, and a side vent near the tunnel end can reduce the peak pressure by 42~78% and the oscillation peak by 35~87%. The peak pressure, oscillation peak, and duration of oscillation rise stage varied significantly with the gas cloud volume. When the premixed gas cloud is ignited at the 1/4 L, the peak pressure and oscillation peak reach the maximum of 1242.5 kPa and 490.4 kPa for confined cases, which are one time higher than those of side-vented cases. What is more, based on the equivalent single degree of freedom (SDOF) approach in the elastic range, the dynamic effects of gas explosions in utility tunnels are figured out, and suggestions for engineering practice are proposed.