Influence of Stationary Vehicles to Thermal Fume Backlayering Length in Tunnel Fire

Abstract

This research is using methods model experiments and numerical simulation in tunnel respectively to discuss what influence that stationary vehicles located in upwind fire source would have on backlayering length Lb of thermal fume. In this experiment, the same scale of the fire source was adapted, and the variables are the obstacles height of upwind fire source. There are two kinds of obstacles: lower obstacles and higher ones; the configuration is divided into two kinds: no stationary vehicles (M0) and both sides of stationary vehicles (M2). This experiment is using 1/5 model of the tunnel, and the model material Biot number and Fourier number is close to the full-scale tunnel. In terms of numerical simulation, a full scale model was built by original code which is self-developed and then calculated the fire source scale and time range of quasi-steady used in numerical simulation with dimensionless formula and Froude scaling methods respectively. Comparing the relation between dimensionless backlayering length Lb/H and Q*1/3/Fr with curve fitting equation proposed by Kunikane (11th International Symposium on AVVT, Luzern, Switzerland, pp. 87–101, 2003 [1]), it shows that under the same Froude number circumstance, the Lb with obstacles is shorter than that without obstacles. Also, model experiments and numerical simulation both show similar result. Thus the original code used for numerical simulation in this study is suitable for studying the effect of stationary vehicles on Lb. After analyzing the effect of stationary vehicles on the longitudinal velocity, it is found that in the case of M2, the longitudinal velocity on the upper part of the tunnel is bigger than that of M0. Therefore, the Lb in M2 is shorter than that in M0. Because, in the case of M2, higher obstacles cause the wind speed of the upper part of the tunnel to become faster, which in turn causes the Lb to become shorter and the slope of the fitting curve to become smaller.