An experimental study on critical velocity in sloping tunnel with longitudinal ventilation under fire

Abstract

Experiments based on Froude scaling law were conducted in a 1/10 reduced-scale model tunnel to investigate the effect of slope on critical velocity in tunnel with longitudinal ventilation under fire. Methanol pool fire was used as the fire source. Smoke movement in the model tunnel with different combination of tunnel slope (−3%, −1.8%, −1%, 0%, 1%, 1.8% and 3%) and longitudinal ventilation velocity was studied. The longitudinal distribution of temperature and velocity were measured. Critical longitudinal ventilation velocity for arresting smoke back flowing in the model tunnel was investigated. Critical velocity in horizontal tunnel obtained in this study was used to compare with that of previous studies. The experimental results agreed well with the model proposed by Wu and Bakar. Correlation between the critical velocity and the slope of the tunnel is proposed based on the experiment results. As the tunnel slope increases from downhill to uphill, critical velocity decreases nearly at a rate independent of the heat release rate of the fire source. The correlation proposed in this studied agrees well with the equation adopted in the Subway Environment Simulation Computer Program (SES). However, it has some discrepancy with the expressions proposed by Atkinson and Ko et al. based on their experimental results. The cause of the discrepancy is attributed to different configuration of the experiments.