This paper explores the smoke flow characteristics in tunnel fires,giving a particular emphasis on the effects of different distances between the smoke outlets and the fire source.It examines the smoke behavior under ...This paper explores the smoke flow characteristics in tunnel fires,giving a particular emphasis on the effects of different distances between the smoke outlets and the fire source.It examines the smoke behavior under different conditions,including variations in heat release rates,exhaust volumetric flow rates,spacing between smoke outlets,and the longitudinal fire source positions.Results indicate that altering the fire source positions and the smoke outlets in the tunnel leads to variations in the properties of smoke flow both the fire source upstream and downstream;the distance between fire source and smoke outlet increases gradually,airflow rate decreases initially and eventually reaches a stable state.Similarly,smoke mass flow rate exhibits an increasing trend that eventually reaches a stable state.Moreover,the heat exchange between the tunnel walls and hot smoke increases as the smoke outlet moves further away from the fire source.This interaction leads to a reduction in the heat exhaust coefficient and a decrease in the distance the smoke spreads.This study investigates the impact of altering the relative longitudinal fire source positions and smoke outlet on smoke flow characteristics by numerical simulation.A theoretical analytical method is used to give a predictive model for the heat exhaust coefficient and the smoke spreading distance.This research can support the theory and technical process of tunnel smoke exhaust prevention and control.展开更多
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...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 aW-shaped distribution.The congestion situation does not allowfor 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 fromthe fire source.The tunnel slope inversely affects the smoke mass flowrate at the same location.The results can be utilized as a reference for conducting evacuation operations and aiding rescues during aW-shaped tunnel fire.展开更多
The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effe...The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effect in the tunnel,and the influence of different design parameters on the smoke exhaust effect and temperature attenuation of the tunnel can help engineers in designing a more effective centralized smoke exhaust system for the tunnel.In this paper,the Fire Dynamic Simulator(FDS)is utilized to examine smoke exhaust vent settings for a centralized exhaust system in shield tunnel with both flat and sloped conditions,including slopes of+4.5%and−4.5%,under a 30MWfire power with a 150m^(3)/s smoke exhaust rate.The results suggest that maintaining a vent spacing of 60m and a vent size of 4.0 m×1.5 m is a reasonable configuration for centralized smoke exhaust systems in both flat and slope shield tunnels.This choice helpsminimize construction costs and prevent excessive smoke accumulation.It also promotes favorable conditions for maintaining temperature distribution at 2-m height,visibility,smoke spread distance,and temperature below the ceiling,all below the threshold values,while ensuring high smoke extraction efficiency.However,in the slope section,the chimney effect can disrupt exhaust efficiency,visibility,ceiling temperature,and temperature distribution at a height of 2 m.Employing different opening methods,such as having 2 vents up and 4 vents down in a+4.5%slope and 4 vents up and 2 vents down in a−4.5%slope,can help mitigate these effects.Furthermore,the temperature decay formula for shield tunnels follows a bi-exponential decay pattern,and different design parameters of centralized smoke exhaust systems have minimal effects on temperature decay in shield tunnels.展开更多
To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%...To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%.Parameters such as ceiling temperature and airflow velocity are measured.The results indicate that the relationship between smoke back-layering length and tunnel slope can be described as an exponential function.The smoke temperature at the downstream exit first increased and then decreased with a higher slope.The airflow velocity at downstream outlet increased nonlinearity when tunnel slope was less than 8%.In the slope tunnel,the fire smoke spread process can be divided into three stages.Fire smoke spreads upstream to the peak distance,subsequently,the upstream smoke layer decreases gradually,the tunnel fire reaches a quasi-steady state.The backflow characteristics of smoke in sloped tunnels are coupled with the downstream length and outlet smoke temperature.In the initial stage of a slope tunnel fire,smoke spreads upstream for a long distance,endangering human health.展开更多
文摘This paper explores the smoke flow characteristics in tunnel fires,giving a particular emphasis on the effects of different distances between the smoke outlets and the fire source.It examines the smoke behavior under different conditions,including variations in heat release rates,exhaust volumetric flow rates,spacing between smoke outlets,and the longitudinal fire source positions.Results indicate that altering the fire source positions and the smoke outlets in the tunnel leads to variations in the properties of smoke flow both the fire source upstream and downstream;the distance between fire source and smoke outlet increases gradually,airflow rate decreases initially and eventually reaches a stable state.Similarly,smoke mass flow rate exhibits an increasing trend that eventually reaches a stable state.Moreover,the heat exchange between the tunnel walls and hot smoke increases as the smoke outlet moves further away from the fire source.This interaction leads to a reduction in the heat exhaust coefficient and a decrease in the distance the smoke spreads.This study investigates the impact of altering the relative longitudinal fire source positions and smoke outlet on smoke flow characteristics by numerical simulation.A theoretical analytical method is used to give a predictive model for the heat exhaust coefficient and the smoke spreading distance.This research can support the theory and technical process of tunnel smoke exhaust prevention and control.
文摘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 aW-shaped distribution.The congestion situation does not allowfor 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 fromthe fire source.The tunnel slope inversely affects the smoke mass flowrate at the same location.The results can be utilized as a reference for conducting evacuation operations and aiding rescues during aW-shaped tunnel fire.
文摘The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effect in the tunnel,and the influence of different design parameters on the smoke exhaust effect and temperature attenuation of the tunnel can help engineers in designing a more effective centralized smoke exhaust system for the tunnel.In this paper,the Fire Dynamic Simulator(FDS)is utilized to examine smoke exhaust vent settings for a centralized exhaust system in shield tunnel with both flat and sloped conditions,including slopes of+4.5%and−4.5%,under a 30MWfire power with a 150m^(3)/s smoke exhaust rate.The results suggest that maintaining a vent spacing of 60m and a vent size of 4.0 m×1.5 m is a reasonable configuration for centralized smoke exhaust systems in both flat and slope shield tunnels.This choice helpsminimize construction costs and prevent excessive smoke accumulation.It also promotes favorable conditions for maintaining temperature distribution at 2-m height,visibility,smoke spread distance,and temperature below the ceiling,all below the threshold values,while ensuring high smoke extraction efficiency.However,in the slope section,the chimney effect can disrupt exhaust efficiency,visibility,ceiling temperature,and temperature distribution at a height of 2 m.Employing different opening methods,such as having 2 vents up and 4 vents down in a+4.5%slope and 4 vents up and 2 vents down in a−4.5%slope,can help mitigate these effects.Furthermore,the temperature decay formula for shield tunnels follows a bi-exponential decay pattern,and different design parameters of centralized smoke exhaust systems have minimal effects on temperature decay in shield tunnels.
基金National Nature Science Funds of China[No.52106185]Fellowship of China Postdoctoral Science Founda-tion[No.2021M693042].
文摘To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire,a series of tunnel fire models are built by fire dynamics simulator(FDS),with a slope varies from 0 to 10%.Parameters such as ceiling temperature and airflow velocity are measured.The results indicate that the relationship between smoke back-layering length and tunnel slope can be described as an exponential function.The smoke temperature at the downstream exit first increased and then decreased with a higher slope.The airflow velocity at downstream outlet increased nonlinearity when tunnel slope was less than 8%.In the slope tunnel,the fire smoke spread process can be divided into three stages.Fire smoke spreads upstream to the peak distance,subsequently,the upstream smoke layer decreases gradually,the tunnel fire reaches a quasi-steady state.The backflow characteristics of smoke in sloped tunnels are coupled with the downstream length and outlet smoke temperature.In the initial stage of a slope tunnel fire,smoke spreads upstream for a long distance,endangering human health.
