During a fire in a naturally ventilated tunnel with multiple vertical shafts, some shafts may induce supplementary airflow, leading to destabilization the smoke layer and potentially causing smoke to ingress back into the tunnel interior, thereby compromising the safety of trapped occupants. This study investigates the dynamics of smoke propagation in tunnel fires under natural ventilation conditions in multiple shafts using numerical simulations. Various auxiliary measures to mitigate the destabilization of the smoke layer in the tunnel as well as to suppress the smoke propagation are proposed and evaluated. The research findings indicate that installing auxiliary fans inside the shafts or incorporating coupling plates beneath them can effectively attenuate the extent of smoke ingress to varying degrees. While these measures have a small effect on smoke removal efficiency, the auxiliary fans mitigate the collision between smoke flow and supplementary air by regulating the flow field at the bottom of the shaft, maintaining a stable smoke layer flow state and suppressing smoke backflow. Coupling plates increase resistance to horizontal smoke spread. This constrains smoke spread and prevents smoke flow from colliding head-on with supplementary air, which could cause backflow. In summary, this research enhances understanding of the intricate dynamics of smoke propagation in tunnels with multiple shafts during fires and offers insights to refine the design of natural ventilation systems in tunnels.

The back-layering length is a key parameter for evaluating the effectiveness of smoke control in tunnel fires. To investigate the influence of mobile smoke exhaust equipment (MSEE) layout parameters under different deployment conditions, this study combines 1:20 scale tunnel model experiments with fire dynamics simulator (FDS) to conduct the research. The results indicate that the back-layering length is influenced by multiple factors, including the fan height, the distance to the fire source, and the fan flow rate. It is negatively correlated with the fan height within a certain range. At relatively low fan mass flow rates, positioning the fan away from the fire source helps shorten the back-layering length, and placing the fan outside the tunnel can more effectively suppress smoke back-layering. This is because the jet requires a certain distance to develop; if placed too close, the fan momentum tends to reach local equilibrium with the smoke layer, and the jet effect is limited, failing to fully cover the smoke layer. Placing the fan outside the tunnel allows entrainment of more air, enhancing the jet's effect on the smoke layer and significantly suppressing back-layering. In contrast, under high mass flow rate conditions, the optimal exhaust position gradually shifts toward the interior of the tunnel, as the strong jet can effectively drive airflow within the tunnel and more efficiently suppress the smoke layer. In addition, this study develops a dimensionless model for predicting the back-layering length, which is related to the layout parameters of the MSEE. The predicted results show good agreement with both numerical simulations and experimental data.

Tunnel fire research typically assumes that the internal fire plume is symmetrically distributed, overlooking the asymmetric effects of changes in the longitudinal fire source position on the flow field structure. To investigate the impact of the longitudinal fire source position on smoke propagation characteristics and smoke back-layering length, a 1:20 scaled tunnel model was constructed. Twenty-four experimental cases were conducted to examine the effects of fire source location, heat release rate, and ventilation velocity on smoke back-layering length, and the results were compared with numerical simulations. The study indicates that the longitudinal fire source position significantly influences the flow field structure within the tunnel by altering the distribution of longitudinal resistance upstream and downstream, as well as the direction of the total induced airflow. As the fire source moves from the inlet toward the outlet, the effect of induced airflow on longitudinal ventilation shifts from synergistic enhancement to reverse blocking, causing a significant reduction in the effective wind speed within the tunnel. Consequently, under identical ventilation conditions, the closer the fire source is to the downstream portal, the longer the smoke back-layering length. Furthermore, a dimensionless prediction model for smoke back-layering length, incorporating the longitudinal fire source position, was developed. The pre-diction results agree well with numerical simulations and experimental data, with relative errors controlled within 620%.

Metropolitan city express line tunnels are fully enclosed and often span long distances between stations, allowing multiple trains within a single interval. Traditional segmented ventilation ensures only one train per section, but ultra-long tunnels with shaftless designs introduce new challenges under fire conditions. This study investigates smoke behavior in an ultra-long inter-district tunnel during multi-train blockage scenarios. A numerical model evaluates the effects of train spacing, fire source location, and receding spacing on smoke back-layering, temperature distribution, and flow velocity. Results indicate that when train spacing exceeds 200 m and longitudinal wind speed is above 1.2 m/s, the impact of train spacing on smoke back-layering becomes negligible. Larger train spacing increases back-layering under constant wind speed, while higher wind speeds reduce it. Fire source location and evacuation spacing affect the extent and pattern of smoke spread and high-temperature zones, especially under reverse ventilation conditions. These findings provide quantitative insights into fire-induced smoke dynamics in ultra-long tunnels, offering theoretical support for optimizing ventilation control and evacuation strategies in urban express systems.

In extra-long urban rail transit tunnels, fires create a unique double narrow space between the tunnel and the train, making high-temperature smoke discharge difficult and increasing evacuation and rescue distances. This study investigates the temperature distribution of a commuter express carriage fire using a 1:15 scale tunnel model. The effects of heat release rate, number of side doors, and door opening modes were considered. Results show that the fire source's relative position to the side door and the door opening modes significantly influence temperature distribution inside the carriage and tunnel. Three distinct transverse temperature patterns beneath the carriage ceiling were identified. A maximum temperature rise prediction model was developed, incorporating structural correction factors to account for flame deflection under different door opening conditions, achieving an error within 30 %. Additionally, the longitudinal temperature decay beneath the carriage roof follows an exponential trend. A piecewise model was proposed, showing that the decay rate is influenced by the heat release rate, opening factor, and gangway door status. This study provides a quantitative framework for evaluating temperature distribution characteristics during carriage fires in tunnel-train narrow spaces and offers theoretical guidance to improve the safety of passengers and vehicles in extra-long urban rail transit tunnels.

In this work, the effect of various exhaust parameters on the smoke propagation laws under the multi-point centralized exhaust mode are investigated through numerical simulations. The research variables include heat release rate (HRR), exhaust volume, vent spacing, and total area of open vents. Results show that increasing the exhaust volume decreases the maximum temperature rise (Delta Tmax), while increasing the other three factors increases the maximum temperature rise. The longitudinal temperature of the smoke below the tunnel ceiling shows an exponential decay. The exhaust vent velocity is influenced by the exhaust fan, exhibiting an Wshaped distribution. Moreover, the exhaust efficiency of the system improves with increasing extracted volume, but decreases as HRR, vent spacing, and total area of open vents increase. Eventually, the predictive model for the dimensionless back-layering length under multi-point centralized smoke extraction was developed through theoretical analysis. The results indicate that the backflow length becomes larger with increasing HRR, while it decreases with the increase in the other three variables. The results can provide a reference for understanding the smoke behavior under multi-point centralized smoke exhaust, and offer guidance for smoke control, determination of safe evacuation zones, and firefighting rescue.

Natural products are considered as potential sources of leading compounds and play an important role in drug discovery. The liquid chromatography-mass spectrometry (LC-MS) technique is a powerful tool for compound-guided isolation from natural products. In this study, a high-efficiency integrated strategy was adopted to improve the new leading compounds discovery, including offline two-dimensional (2D) LC to extend the peak capacities, target neutral loss (NL) data-dependent acquisition (DDA) for barrigenol-type triterpenoids saponins and automatic screening through predicted natural product screening (PNPS) in TraceFinder. To validate the integrated strategy, the shell of Xanthoceras sorbifolium Bunge (XSB) was taken as a case. An offline 2D-LC system was constructed with hydrophilic interaction chromatography (HILIC) and reversed phase (RP) C18 column, and orthogonality of 0.66 and peak capacity of 3494. The 2D-LC system improved chromatographic baseline separation and peak resolution. Full MS/all ion fragmentation (AIF)/NL dd-MS2 DDA was employed for the detection of the barrigenol saponins. PNPS strategy was adopted and markedly extended the screening coverage. The combined strategy showed about 5 times improvement in the screening capability. The PNPS screening process, using TraceFinder software, discovered a total of 752 barrigenol saponins from the shell of XSB, including 707 potentially new barrigenol saponins, accounting for 94.02%. The feasibility of the strategy was also confirmed by the isolation of two novel barrigenol saponins, the structures of which were unambiguously identified using nuclear magnetic resonance (NMR). Furthermore, this strategy could also be applied to rapidly discover new bioactive constituents from other herbal medicines or other natural sources, especially the barrigenol saponins constituents.

The tunnel with building beams is a new type of tunnel that combines an above-ground building with an underground tunnel to save space in the city. These tunnels have dense beams on the tunnel ceiling for load-bearing. When jet fans work, a large resistance is generated in the tunnels with building beams. In this study, numerical simulation models of tunnels with different beam sizes were built and used to obtain the velocity and pressure distributions. The results show that the pressure of jet fans is lower. The tunnel velocity affects the air entrained in the fan inlet section. Depending on the ratio of beam height to beam spacing, three different flow regimes are produced. The dimensionless beam size L* is introduced to describe the flow regime in the tunnel. When L* <20, skimming flow and wake interference flow are dominant， which has little influence on jet fans. When L* >20, isolated roughness flow is dominant. The velocity and pressure in the tunnel are maintained at a low level, which has a negative impact on jet fans. Results can help engineers estimate the impact of beam size on jet fans and improve tunnel ventilation systems.

Previously, research on blockages was primarily focused on ordinary single tunnels. This paper investigated the temperature decay and smoke propagation characteristics in underground interconnected tunnel with blockages. Considering various blockage ratios, ventilation velocities, and heat release rates (HRRs), 120 experiments were conducted on a model-scale underground interconnected tunnel. It was found that the ventilation schemes and HRR minimally impact the downstream temperature decay pattern. Nevertheless, as the blockage ratio increased, the temperature decay coefficient K initially increased and then decreased. Smoke entry into the connected tunnel was evaluated by the Froude number, and as the blockage ratio increased, the critical Froude number gradually decreased. Examining smoke backflow in underground interconnected tunnel under diverse conditions revealed that the smoke back-layering length was primarily influenced by D-ramp velocity. A predictive model for smoke back-layering length was proposed, considering blockage ratios. The outcomes of this research could help control smoke within underground interconnected tunnels with blockages.

Uniclinal V-shaped structures are common in underground spaces such as mines, tunnels, and subway stations, but few studies have paid attention to its fire smoke movement law. The paper focused on the relationship between air transport velocity, smoke backlayering length, and maximum smoke temperature rise with underground space width and slope. The air transport velocity was quantified, the forecasting model of smoke backlayering length was proposed, and the pattern of variation in the maximum temperature rise was unveiled. The findings indicated that the air transport velocity relates to slope height and buoyancy flux per unit width. The slope has a great influence on the air transport velocity. For the low heat release rate, the backlayering length is primarily determined by the underground space geometry, while for the high heat release rate, it is influenced by the air transport velocity. In contrast to the horizontal underground space, the maximum smoke temperature rise of the uniclinic V-shaped underground space exhibited a linear decrease. When the dimensionless slope height is less than or equal to 1.2, the maximum temperature rise is independent of the section width. When the dimensionless slope height is greater than or equal to 1.6, the maximum temperature rise decreases with the lessening of the section width. These findings contribute to a better understanding of smoke movement in uniclinic V-shaped underground spaces under natural ventilation and provide valuable guidance for smoke control strategies.

Called island-crossing tunnels, some specific underwater tunneling projects face constraints imposed by geological and water conditions, necessitating their passage through artificial or natural islands. The longitudinal of the tunnel follows a W-shaped distribution. The congestion situation does not allow for immediate longitudinal smoke exhaust at the early stage of the fire, and the natural spread of smoke is complicated. An exhaustive investigation was carried out to analyze the smoke behaviors during a fire incident, employing the fire dynamics software FDS, considering five slopes and four fire locations. The simulation results reveal that the layer of high-temperature smoke becomes thicker as one gets closer to the fire source. The thermal pressure difference significantly impacts the temperature distribution within the tunnel and the distance of smoke spread. The value of the thermal pressure difference is significantly affected by changes in slope. It reaches a maximum of 157 Pa at a 5% slope, while it is only 41 Pa at a 1% slope when the fire occurs at the V-point. Fire hazards vary across locations within the W-shaped tunnel, necessitating separate consideration of the V-point and inverted V-point fire characteristics. The mass flow rate in small and large slope tunnels shows different decay rates due to variations in the main forces acting on the movement. Hence, two equations have been developed to predict the smoke mass flow rate, indicating a nonlinear relationship with the tunnel slope and the distance from the fire source. The tunnel slope inversely affects the smoke mass flow rate at the same location. The results can be utilized as a reference for conducting evacuation operations and aiding rescues during a W-shaped tunnel fire.

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特长或超长盾构隧道中普遍应用顶部集中排烟模式.为了揭示隧道火灾顶部集中排烟模式烟气层化高度和范围,经过全尺寸隧道现场热烟测试发现,集中排烟模式下烟气可以形成稳定分层且被控制在一定范围内.通过数值模拟方法研究了不同热释放速率、排烟量、排烟阀数量和间距情况下烟气层化高度和范围.研究结果表明:1)针对热释放速率为5～50 MW,不同热释放速率工况下排烟系统均能将烟气层化范围控制在一定距离内.随着热释放速率增加,烟气层化范围增大.排烟阀开启范围之内,热释放速率增大,烟气层化高度差距较小.排烟阀开启范围之外,热释放速率越大,烟气层化高度越低.2)针对热释放速率为50 MW,排烟量为120～260 m3/s,不同排烟量工况,排烟阀开启范围内烟气层化高度变化小,开启范围之外烟气层化高度变化大.烟气层化范围随着排烟量增大而变小,可有效控制烟气分布区域.因此建议工程设计、运营过程中可在允许范围内提高排烟量.3)针对排烟阀间距为40～140 m,排烟阀数量为4～8个,增大排烟阀间距和增加排烟阀数量,会导致烟气层化高度降低,烟气层化范围增加,排烟阀数量对烟气层化高度和范围影响较大.

近年来,越来越多的城市轨道交通车辆基地采用了带上盖物业开发的形式.为降低风亭排出烟气对带上盖物业开发车辆基地上盖建筑的影响,提出一种车辆基地排烟风亭外部结构挡板及其工程应用方案,并通过数值模拟方法研究不同挡板形式、角度、宽度、长度及挡板与风亭间距条件下的上盖建筑处温度、CO浓度分布.研究结果表明:1)上盖建筑处的温度、CO浓度变化趋势一致,烟气中CO对上盖建筑影响大于温度,工程设计中应以CO浓度作为首要判断标准.2)上盖建筑受烟气影响程度与风亭挡板的结构形式密切相关,受挡板的引流作用与烟气自身热浮力的影响,在风亭排烟口外侧设置与风亭不相连的挡板可有效减少烟气对上盖建筑影响.3)随着挡板角度、挡板与风亭间距的增加,上盖建筑受烟气影响程度先减少后增加,建议工程中挡板角度不大于30°,挡板上沿与风亭间距介于0.4～1.6 m之间.4)随着挡板宽度与长度的增加,排烟口正前方建筑受烟气影响逐渐减少,但排烟口两侧建筑受烟气影响逐渐增加,建议工程中挡板宽度介于排烟口长度与风亭长度之间,挡板下沿与排烟口下沿齐平.

To investigate the fire risk in a complex tunnel with varying cross-sections, sloped structures, and dense upper cover beams, this study considered four fire source positions: the immersed tube section, confluence section, highway auxiliary road section, and four-lane sections of the main line. It also considered four beam spacings: 1 m, 1.8 m, 3.6 m, and 7.2 m. The Fire Dynamics Simulation Software FDS was utilized to create a comprehensive tunnel model. The analysis focused on temperature and visibility changes at a 2 m height under a 20 MW fire condition for different fire source positions. These changes were then compared with critical danger values to assess the safety of evacuating personnel within the tunnel. Subsequently, this study proposed corresponding emergency rescue strategies. The findings indicated that when the beam grid spacing exceeded 3.6 m, the upper dense beam gap showed a robust smoke storage capacity, leading to a reduced distance of high-temperature smoke spread. However, this increased smoke storage disrupted the stability of the smoke layer, resulting in a heightened smoke thickness. The location of the ventilation vent at the entrance of the immersed tunnel section caused a non-uniform ventilation flow under the girder, deflecting the smoke front towards the unventilated side and decreasing visibility in the road auxiliary area. In comparison to scenarios without a beam lattice, the presence of a beam lattice in the tunnel amplified fire hazards. When the beam lattice spacing was 3.6 m or greater, the extent of the hazardous environment, which is unfavorable for personnel evacuation, expanded. With the exception of the scenario where the fire source was located in the highway auxiliary roadway, all other conditions surpassed 150 m, which is roughly one-third of the tunnel length. Consequently, more targeted strategies are necessary for effective evacuation and rescue efforts.

面对城市内河存有江中岛情况,过江隧道普遍采用"W"型的纵断面形式.揭示城市"W"型过江隧道火灾烟气运动规律具有重要意义.利用火灾动力学软件(FDS),采用数值模拟方法研究了交通正常、拥堵工况下城市"W"型中长距离沉管隧道火灾烟气蔓延范围和隧道顶部温度、流速分布规律.结果表明:交通正常时,临界风速可以较好控制城市"W"型隧道内不同区间发生火灾时的烟气;交通拥堵时,沙岛段发生火灾时危险性最高,1 800 s 时烟气还有继续蔓延的趋势.交通正常时隧道顶部最高温度均小于 300℃;交通拥堵时,沙岛段隧道顶部最高温度约423℃,沉管段隧道顶部最高温度约 387℃,出入口段隧道顶部最高温度约 350℃～400℃.交通正常时,火源下游流速明显高于上游流速;交通拥堵时,火源处流速最大,随着距离增加,流速整体呈现衰减趋势,隧道顶部流速会随坡度变化波动.

In recent decades, with the rapid development of the economy and tunnel construction technology, an increasing number of underwater road tunnels have been constructed in China. Underwater road tunnels play a crucial role in transportation hubs that connect cities and regions. Underwater tunnels have strong closures, which makes evacuation and rescue difficult. Therefore, personnel evacuation in emergencies, such as fires, has become a critical problem that needs to be solved. A full-scale evacuation experiment in an underwater shield tunnel with 188 participants was conducted to explore the characteristics of personnel evacuation behavior under the blocked condition of an underwater shield tunnel in the case of fire. The time of fire detection and personnel response, alighting time of passengers from vehicles, opening time of the stair-cover plate, evacuation capacity of stairs, and relationship between the evacuation speed and age and gender of participants were obtained. The experimental results showed that the driver's actions had a strong demonstrative effect, and the improvement of the driver's efficiency in handling emergencies could promote the evacuation process. The average alighting time per bus passenger was 1.41 & PLUSMN; 0.53 s, and proper personnel guidance, good road conditions, and increased tunnel familiarity reduced it. The average evacuation capacity of the stairs was 33.3 & PLUSMN; 4.1 person/min. When the proportion of older adults increased from 0 % to 10.64 %, the evacuation capacity of stairs decreased by approximately 8.5 %. The evacuation capacity of stairs can be significantly improved through reasonable or-ganization and evacuation guidance. However, as the number of people gathered at the stair entrance gradually increased, the "bottleneck" effect became significant, and the evacuation capacity was primarily controlled by its structure at this time. The average evacuation speed for male and female was the same in good road conditions, about 1.39 m/s, but decreased significantly in blocked conditions, to 0.72 m/s and 0.48 m/s, respectively. Further, it decreased to 1.27 m/s and 1.23 m/s, respectively, in the secure channel, which may be related to the psychological state of relaxation and slackening and the increase in road pavement roughness.

This study investigated the air entrainment caused by a lateral smoke exhaust system via full-scale and model-scale tests. A particular phenomenon, shear flow, was observed downstream of the exhaust vent. The phenomenon of shear flow was more intense when the exhaust velocity increased, which destroyed the smoke layer stratification and strengthened the air entrainment. Plug-holing and shear flow intensified air entrainment, and the functional relationship between air entrainment, Froude number, and dimensionless exhaust vent size was established. The relationship between the air entrainment and heat exhaust efficiency was studied, and it was found that the heat exhaust coefficient was positively related to the air entrainment. The functional relationship between the heat exhaust coefficient and air entrainment for different lateral exhaust vent sizes was presented. In addition, we observed that lateral smoke exhaust exhibit little effect on the centerline temperature distribution. A model that can be used to describe the centerline temperature distribution with lateral smoke exhaust systems was developed.

Under the boundary condition of single sidewall constraint, this study investigates the relationship between the window dimension, heat release rate, and sidewall distance and the development law of the mean flame height. Based on the characteristic length scale of the window of the combustion chamber l1 = (AV)2/5 as the dividing point, the mean flame height variation law with sidewall distance D is revealed to be as follows: for l1<D, as the distance between the sidewalls increased, the mean flame height did not change significantly; for l1/2 <= D <= l1, a decrease in the distance between the sidewalls increased the mean flame height. A flame entrainment model under sidewall constraint boundary conditions was developed based on the evolution law of mean flame height and flame entrainment characteristics of the window to describe the difference in mean flame height between the free boundary without a sidewall. Furthermore, the limit boundary of a sidewall, the mean flame height correction factor K was introduced. The non-dimensional mathematical expression of the mean flame height under a single sidewall constraint boundary condition was established and verified.