Effects of blockage on the flame morphologic characteristics in a ventilated tunnel

As a practical but seldom concerned issue, the morphologic characteristics of a turbulence diffusion flame under the effects of upstream blockage in a longitudinally ventilated tunnel was studied based on a series of model-scale experiments. Different blockage sizes, blockage-fire distances, longitudinal ventilation velocities, and fire sizes were considered for research. Numerical simulations were also carried out to calculate the flow field for analyzing the causes of the variety in the flame morphology and determining the length of the near wake. Experimental results showed that the flame morphology can be divided into two stages according to the dimensionless blockage-fire distance normalized by the length of the near wake, namely flame bifurcation and flame tilt. By comparing with previous literature, the critical blockage-fire distance corresponding to the symmetrical bifurcation was achieved which follows a linear relationship with the length of the near wake. On the basic of tilt angle and centerline trajectory, dimensionless models were developed to predict the flame tilt under the effects of blocking ratio and blockage-fire distance. The research outcomes can provide a reference and tool to assess the fire risks of tunnels with blockage effects.