Study on the smoke propagation characteristics of metro tunnel fire under the effects of piston wind

Abstract

Metro trains running in tunnels cause piston wind, and when a metro train stops in a tunnel due to a fire, the effect of the piston wind on smoke propagation characteristics cannot be ignored. In this paper, a theoretical model based on the unsteady flow theory of the Bernoulli equation was established to describe the change in piston wind speed under fire conditions. The characteristics of the smoke propagation in tunnel fires under the effect of the piston wind were analysed by means of numerical simulation. The result indicates that the piston wind has a significant effect on the characteristics of smoke distribution. In a longitudinally ventilated tunnel, whether the direction of piston wind is the same as that of longitudinal ventilation could seriously affect the control of fire smoke. When the direction is the same, the piston wind could enhance the smoke control effect of the longitudinal ventilation. Otherwise, the smoke control effect could be significantly diminished, and the smoke control by the critical wind speed of longitudinal ventilation would fail. The findings could contribute to a better understanding of the characteristics of tunnel fire to control smoke spread under the influence of piston wind.

Effect of metro train on the critical driving force for preventing smoke back‐layering in tunnel fires

“…44,55 Heptane was adopted as the fuel, which has been used by other researchers in metro tunnel fire simulation studies. [56][57][58] According to the previous studies, 4,16 the size of the subway tunnel fire is generally within the range of 5-10 MW. In this study, five heat release rates equal to 5, 6, 7.5, 9, and 10 MW were employed.…”

“…In all of the simulations, the fire source with a dimension of 2 m (length) × 2 m (width) × 1 m (height) was located at the tunnel ceterline in front of the train head 44,55 . Heptane was adopted as the fuel, which has been used by other researchers in metro tunnel fire simulation studies 56‐58 . According to the previous studies, 4,16 the size of the subway tunnel fire is generally within the range of 5‐10 MW.…”

“…The fire source was defined as “BURNER” with the specification of heat release rate per unit area 22 . Consider the most unfavorable conditions, all simulations concern quasi‐steady state conditions with fixed heat release rate 56,58 …”

“…22 Consider the most unfavorable conditions, all simulations concern quasisteady state conditions with fixed heat release rate. 56,58 Details of the FDS simulation cases are summarized in Tables 2 and 3. For the simulation cases without fire, values in Table 2 were used to obtain the pressure loss caused by the tunnel boundaries and metro train blockage.…”

Effect of the Metro Train on the Smoke Back-Layering Length under Different Tunnel Cross-Sections

“…In this paper, we set HRR as 5 MW and 7.5 MW. Considering the most unfavorable conditions, all simulations considered quasi-steady state conditions with fixed HRR [41]. Several typical HRR curves, which are under 0.6 m/s wind speed in Tunnel A, are presented in Figure 5.…”