Numerical simulations of dynamics of a tunnel fire.

摘要

Tunnel fires are very important in many studies of fire safety and risk assessment as they may cause significant property damages as well as human casualties. The present study investigated the effects of ventilation on a tunnel fire using numerical simulations. The simulations were carried out using a commercial computational fluid dynamics (CFD) code, CFX 5.6, from Ansys Inc. Simulations considered physical models for turbulence, combustion, buoyancy, and radiation. The simulations were first validated by comparing the results with the experimental data from the literature and good agreements were obtained. Temperature distributions, hot gas concentration profiles, backlayering, and wall heat flux distributions were studied. Effects of ventilation velocities, additional ventilations, ventilation spacing, turbulence models, grid sizes, fuel types, and different heat release rates, were explored. The present work showed that ventilation velocity is the most important factor in a tunnel fire. Introduction of additional ventilation reduced the maximum temperatures, mass fractions of toxic gases such as CO, and their spread throughout the tunnel. CO mass fraction was found to be maximum in the vicinity of the fire. With increase in the heat release rates, temperatures and mass fractions of combustion products increased. Turbulence models and grid sizes had negligible effects on the simulation results. For the same heat release rate, changing fuel type had very small effects on the temperature distributions and other characteristics of the fire. Wall heat fluxes were maximum near the fire and continuously decreased downstream of the fire.