Numerical study of the effects of ventilation velocity on peak heat release rate and the confinement velocity in large tunnel fires

Abstract

The longitudinal ventilation system in a tunnel can force fire hazards to propagate downstream, and meanwhile the fresh airflow carries oxygen to the fire source, which can enhance combustion process. This paper numerically investigated the effects of longitudinal ventilation velocity on peak heat release rate (HRR) for large tunnel fires. The simulation results show that the dimensionless HRR increases linearly with the increase of dimensionless ventilation velocity. The growth rate was found to linearly correlate with the dimensionless fuel supply. The length of back-layering was significantly reduced if the dimensionless ventilation velocity reached 70% of dimensionless critical velocity. This phenomenon provides a method to find a “confinement velocity” to prevent smoke flow further spreading upstream in tunnel fires. The simulation results were also compared with some experimental data to evaluate the finding in this study.