Effect of lateral concentrated smoke extraction on the smoke back-layering length and critical velocity in a longitudinal ventilation tunnel

In this study, the thermal smoke back-layering behavior and critical ventilation velocity of tunnel fires were investigated experimentally under the combined effect of lateral concentrated smoke extraction and longitudinal ventilation. The smoke back-layering length, critical ventilation velocity, and confinement velocity were analyzed and discussed. The results indicate that the smoke back-layering length decreases with increasing lateral concentrated smoke extraction velocity when the longitudinal ventilation velocity is less than the confinement velocity. However, above the confinement velocity, the smoke back-layering length increases with increasing lateral concentrated smoke extraction velocity. The critical velocity also shows an increasing trend with an increase in the lateral concentrated smoke extraction velocity. Finally, a correlation equation for the critical velocity of tunnel fires under the combined effect of lateral concentrated smoke extraction and longitudinal ventilation was proposed.