Research on the influence of different heat release rates on the throttling effect and critical wind speed in tunnel engineering

Nowadays, on account of effectively limiting the spread of the fire, minimizing the potential for high-temperature damage to the tunnel structure, longitudinal ventilation system has been widely used to safeguard the overall safety and operational integrity of the tunnel. In longitudinal ventilation tunnel fires, the intensity of the fire heat release rate (HRR) directly affects the performance of the ventilation system, leading to what is known as the "Throttling Effect".This study focused on the throttling effect, resulting in the reduction in airflow, which was a major concern in the longitudinal ventilation tunnel fires. A full-scale Memorial Tunnel model was conducted by using the Fire Dynamics Simulator (FDS) 6.9.1. The impact of the number and location of operating fans on the the throttling effect and the critical air velocity under three different HRR was investigated in this study. The results showed that for 10 MW case, the reduction in airflow ranged from 4% to 7%. It can be concluded that the greater the HRR of the fire, the greater the airflow resistance, leading to the decrease of the airflow velocity through the tunnel.