A study on the effects of the slope on the critical velocity for longitudinal ventilation in tilted tunnels

Li, J.; Li, Y.F.; Cheng, C.S. Agnes; Chow, Wan Ki

doi:10.1016/j.tust.2019.04.015

Cited by 49 publications

(10 citation statements)

References 12 publications

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“…The formula to calculate the critical velocity C u in inclined tunnels uses the numerical value of critical velocity ,0 c u of horizontal tunnels as per the following equation [14] ,, c g co u Ku ,…”

Section: Results and Validation Of Modelsmentioning

confidence: 99%

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Analysis of the Parameters of the Fire Modeled in a Road Tunnel

LANCHAVA¹,

ILIAS²,

Radu³

et al. 2021

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The essence of the problem lies in the experimental study of the laws governing the changes in the aerodynamics of air flow and the most important ventilation parameters, taking into account the effect of fire. During the experiments, the aerodynamics of the tunnel is complicated by the presence of additional resistance, and the variables will be: the slope of the tunnel, the heat release rate, the cross section of the tunnel, the ratio of the width of the tunnel to the height, the fill factor of the tunnel by transport. The solution to the problem is an improved ventilation technology in case of fires to save lives. The aim of the research is to study the critical velocity, the backlayering length and the gradient-factor using numerical and physical models, as well as mathematical analysis for the downward movement of fresh air, when the fresh air inlet is above the fire level. The scale of the physical models is 1:40 and 1:60. Numerical models are full scale using of modern engineering technique Pyrosim and Fluent. The generalization of the results is carried out using piece-wise constant functions. The obtained results are also be compared with similar results known from scientific literature.

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Section: Results and Validation Of Modelsmentioning

confidence: 99%

“…The gradient of the experimental tunnel will be up to 10 degrees. As far as we know, there is a tunnel with an 8-degree gradient in Norway, while the maximum gradient of the tunnels in China is 7 degrees [14].…”

Section: Backlayering Determinationmentioning

confidence: 97%

Analysis of the Parameters of the Fire Modeled in a Road Tunnel

LANCHAVA¹,

ILIAS²,

Radu³

et al. 2021

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show abstract

“…There are a number of papers describing different fire development scenarios have been written and published to address this issue. In particular, the peculiarities of underground fires, the smoke propagation under the ground [2][3][4][5][6][7], the temperature distribution in tunnels, the effect of tunnel inclination on back-layering length in case of natural ventilation [8][9][10], and fire development dynamics and scenarios under the ground have been studied, the theoretical and experimental studies of critical velocity have been performed, and the effect of the distribution of smoke and combustion products in the opposite direction of the ventilation flow movement has been identified [11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Influence of current direction in longitudinal ventilated road tunnels on the backflow of combustion Produits

et al. 2022

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The results of numerical modeling in longitudinal ventilated sloping road tunnels are given. The slope of the tunnels varies in the range of 0-6%. The geometry of the tunnel is as follows: length: 100 m; width: 8 m; height: 6 m; area of the seat of fire: 16 m2. The seat of fire sized: 2.75x5.8x1.5 m is in the central part of the tunnel. The scenarios of development of 5, 10, 20, 30, 50 MW fires are studied in the case of positive and negative directional ventilation flows. The time of modelling was 120 seconds. The numerical problems were modelled with a volumetric grid method. The grid cell dimensions were: 0.5*0.5*0.5 m. Virtual point and volumetric measuring equipment was used to record the modeling results. The modelling used 4 groups of measuring devices that measured and recorded air velocity, temperature, and air and smoke densities. The paper discusses cases of algebraically summarizing the ventilation and fire-induced flows. Based on the results of numerical modeling, we can point out that the widely accepted indices of critical velocity and back-layering length in inclined road tunnels often give erroneous results. Therefore, in strategies for emergency ventilation, indicators such are critical velocity and back-separation should be used with caution.

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“…And,

v_{c}^{*} goodbreak= ({, \begin{matrix} 0.83 {Q^{*}}^{1 / 3} ζ \leq 1 \\ 0.79 {Q^{*}}^{1 / 3} ζ > 1 \end{matrix}),

where

ζ

is the section coefficient and defined as

ζ = A / H^{2} .

Following the aforementioned studies, many researchers addressed the influence of other factors, such as tunnel slope, 12,13 fire location, 14 cross section, 15 turning radius, 16 thermal properties of wall materials, 17 ceiling extraction, 18 ambient pressure, 19,20 branch tunnel, 21,22 and water spray 23 . A series of empirical models were subsequently proposed.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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Summary Preventing smoke back‐layering in longitudinal‐ventilated tunnels is an important topic in handling with fires safety issues. Previous studies focused on the critical velocity, while only very few of them paid attention to how to realize this parameter, that is, in a critical state, to overcome the resistance of the tunnel and the fire source to the airflow, the required driving force provided by the ventilation equipment installed in the tunnel. This study addressed this problem in the situation where the coupling effect of blockage and throttling effect was highlighted by conducting theoretical analysis and numerical simulations. The results showed that the presence of metro train blockage reduces the effective cross‐sectional area of the tunnel near the fire source and decreases the critical velocity. On the other hand, the blockage of trains also increases the resistance to the ventilation airflow and exacerbates the throttling effect, leading to the increase of the critical driving force. In such conditions, a stronger driving force to approach the critical velocity was needed. Besides, the length of train blockage was verified to exert limited influence on the value of critical velocity while it significantly affected the critical driving force. Furthermore, the calculated formula for the critical driving force was proposed with the prevention of smoke back‐layering considering the blockage effect to be emphasized.

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A study on the effects of the slope on the critical velocity for longitudinal ventilation in tilted tunnels

Cited by 49 publications

References 12 publications

Analysis of the Parameters of the Fire Modeled in a Road Tunnel

Analysis of the Parameters of the Fire Modeled in a Road Tunnel

Influence of current direction in longitudinal ventilated road tunnels on the backflow of combustion Produits

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

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