Prediction of backlayering length and critical velocity in metro tunnel fires

Weng, Miaocheng; Lu, Xin-Ling; Liu, Fang; Shi, Xiang-peng; Yu, Longxing

doi:10.1016/j.tust.2014.12.010

Cited by 115 publications

(42 citation statements)

References 20 publications

(18 reference statements)

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“…Figure shows the comparison of the critical ventilation velocity between the simulation results and previous research data under the condition of scenarios without metro train. Although there are some differences among previous studies, which are mainly caused by the different experimental set‐up, the simulation results show a good agreement with the previous studies, and most importantly, these values are very close to the Li and Ingason's experimental results , which indicate that the simulation results are acceptable and also validating the good prediction capacity of FDS to investigate the critical ventilation velocity in tunnel fire.…”

Section: Resultssupporting

confidence: 75%

Critical ventilation velocity under the blockage of different metro train in a long metro tunnel

Zhang

Shi

et al. 2020

Fire and Materials

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To address the effect of metro train blockage on the critical ventilation velocity in a long tunnel, a series of scenarios were conducted numerically through this study, including different fire sizes (5-10 MW), metro train lengths (80-120 m), and blockage ratios (φ, 0.50, and 0.57). It is known from the numerical results that the metro train length shows a limited effect on the critical ventilation velocity, which is because the longitudinal ventilation has become stable before reaching the fire source to prevent smoke back-layering, and increasing the metro train length only increases the distance of stabilizing the longitudinal ventilation. The blockage ratio shows an obvious influence on the critical ventilation velocity, which is because the presence of the metro train can obviously reduce the flow cross-sectional area of the tunnel. An empirical model is developed as well, while it is known that the critical ventilation velocity increases with the one-third power of dimensionless heat release rate and (1-φ). The research outcomes of this study provide a technical guide for the design of the metro tunnel and the relevant emergency management of fire rescue under fire conditions. K E Y W O R D S blockage ratio, critical velocity, FDS, metro train, subway tunnel 1 | INTRODUCTION An increasing number of metro systems have been designed and constructed recently to release the urgent issues of accelerated urbanization and growing population in metropolises. The companied fire risk is always an important and hot research topic from both the academia and industries. Consequence and impact of the relevant fire accidents are very high, which can be proved by the large number of fire casualties and very bad influence in the past few decades, such as the Daegu metro fire in South Korea, the Viamala tunnel fire in Switzerland, and the Burnley tunnel fire in Austria. [1][2][3][4] To benefit with the fire safety of those metro systems, smoke movement is an inevitable aspect during the design as it is the most fatal factor of a tunnel fire. 5-7 Therefore, how to control the smoke movement effectively to provide a safe zone for the occupants and firefighters during the evacuation and rescuing processes, respectively, becomes an important question that needs to be answered urgently.It is indicated that the metro train fails to reach the next station and stops between the two stations in about 50% of fires. 8,9 When a fire occurs in the metro tunnel, the relevant ventilation facilities in the adjacent stations will be started, where longitudinal ventilation is triggered, which not only can prevent the smoke from spreading to the upstream and also offer a safe zone without smoke for both occupants and firefighters. If the designed longitudinal ventilation velocity is smaller than the critical value, the smoke released from the fire can break through the barrier raised by the longitudinal ventilation and then threaten the people upstream.Many studies have been undertaken in identifying the appropriate longitudinal ventilation v...

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Section: Resultssupporting

confidence: 75%

Critical ventilation velocity under the blockage of different metro train in a long metro tunnel

Zhang

Shi

et al. 2020

Fire and Materials

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“…The temperature measurement accuracy of the Wu and Bakar experiments is ±2 to 3°C near upstream and downstream of the fire source. There are considerable numerical studies that have validated their numerical results using the Wu and Bakar experimental data.…”

Section: Resultsmentioning

confidence: 99%

Numerical simulation to investigate the induced buoyant flow characteristics caused by intensive heat in complex curvilinear geometries

Savalanpour

Farhanieh

Afshin

2018

Heat Trans. Asian Res.

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The buoyancy-induced turbulent flows in complex geometries with internal heat source have important application in enclosure fire dynamics, for example, smoke movement in the situation of fire in tunnels. The majority of computational works studying the fireinduced hot air movement in such cases use a Cartesian coordinate system. Hence, to simulate curved geometries, the Cartesian grid should be refined so that it comparatively matches the geometry. In the present work, a three-dimensional numerical method using nonorthogonal curvilinear coordinate system was developed. Numerical simulations were performed to study the flow structures and the heat transfer characteristics of fire-induced buoyant flow and the effects of using curvilinear coordinates on the result's accuracy and the computational cost. Numerical results were compared with the available experimental data and the results obtained by fire dynamics simulator (FDS) software. The results of the present method showed better agreement with the experimental results when compared with the FDS results. K E Y W O R D S Buoyant flow, curvilinear coordinate, intensive heat source, numerical study, tunnel fire Heat Transfer-Asian Res. 2019;48:835-853.wileyonlinelibrary.com/journal/htj

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“…Gannouni et al 24 argued that the decrease of critical velocity due to the blockage of vehicle upstream of fire source was related to the location of vehicle from the tunnel floor, and the larger the distance between the obstruction and floor, the smaller the critical velocity. Two models were presented by Weng et al 25 to predict back-layering length and critical velocity in metro tunnels by conducting Computational Fluid Dynamics (CFD) and reducedscale model tests with hydraulic diameter of the tunnel representing the geometrical characteristics of tunnel cross-section. Yi et al 26 conducted a series of reduced-scale experiments to explore effects of slope on the critical velocity and their results fitted well with previous studies.…”

Section: Introductionmentioning

confidence: 99%

“…Two models were presented by Weng et al. 25 to predict back-layering length and critical velocity in metro tunnels by conducting Computational Fluid Dynamics (CFD) and reduced-scale model tests with hydraulic diameter of the tunnel representing the geometrical characteristics of tunnel cross-section. Yi et al.…”

Section: Introductionmentioning

confidence: 99%

Effects of ambient pressure on the critical velocity and back-layering length in longitudinal ventilated tunnel fire

Yan

Wang

et al. 2019

Indoor and Built Environment

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Nowadays, the critical velocity and back-layering length are the key parameters in longitudinal ventilation design. However, most studies research them at standard air pressure but ambient pressure decreases at high-altitude area and the reduced ambient pressure could affect the smoke movement characteristics in a tunnel fire. In order to investigate the effect of ambient pressure on the velocity and back-layering length in longitudinal ventilated tunnel, theoretical analysis was carried out first and a series of numerical simulation were conducted with varying heat release rate and ambient pressure. Results show that Li’s model is also reliable under various ambient pressures. The critical velocity under various ambient pressures would become larger with an increase in the heat release rate and would remain stable after the heat release rate reaches a certain value. At smaller heat release rate, the length of counterflow would be higher under reduced ambient pressure while it remains the same when the HRR is large. This could provide reference for tunnel ventilation design at high-altitude areas.

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Prediction of backlayering length and critical velocity in metro tunnel fires

Cited by 115 publications

References 20 publications

Critical ventilation velocity under the blockage of different metro train in a long metro tunnel

Critical ventilation velocity under the blockage of different metro train in a long metro tunnel

Numerical simulation to investigate the induced buoyant flow characteristics caused by intensive heat in complex curvilinear geometries

Effects of ambient pressure on the critical velocity and back-layering length in longitudinal ventilated tunnel fire

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