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Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering00 211 (2018) 421–426 Procedia Engineering (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000
Influence of Arrangement of Jet Fans on Smoke Exhaust Effect in a Influence of Arrangement of Fans on Smoke Exhaust Effect with Longitudinal Ventilation System 2017 8th International Conference on Fire Science Fire Protection Engineering Influence ofTunnel Arrangement of Jet Jet Fans onand Smoke Exhaust Effect in in aa Influence of Arrangement of Jet Fans on Smoke Effect in a Tunnel Longitudinal Ventilation System (on theawith Development ofa,bPerformance-based Fire Exhaust Code) Influence of Arrangement of Jet Fans on Smoke Exhaust a a Effect in a Tunnel with Longitudinal Ventilation System Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG Influence of Arrangement of Jet Fans on Smoke Exhaust Effect Tunnel with Longitudinal System Influence of Arrangement of Jet FansVentilation on Smoke Exhaust Effect in in aa awith Longitudinal a,b FansVentilation a a Effect in a Tunnel System Influence of Arrangement of Jet on Smoke Exhaust Yun-fei LI *, Yan-feng LIa,b , Xiao FENG HUANG a, You-bo a Tunnel Longitudinal Ventilation Beijing Key Laboratory of Green LI Builtawith Environment and Energy Efficient Technology, Beijing University ofSystem Technology, Beijing, 100124, China Yun-fei *, Yan-feng LIa,b , Xiao FENG , You-bo HUANG Tunnel Ventilation System awith Longitudinal a a Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG Tunnel with Longitudinal Ventilation System College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China a a,b a a Beijing Key Laboratory of Green LI Built *, Environment and Energy Technology, Beijing University of HUANG Technology, Beijing, 100124, China Yun-fei Yan-feng LI Efficient , Xiao FENG , You-bo a a a
b
a University of Technology, Beijing, a Beijing Key Laboratory of Green Builtaa Environment and Energya,b Efficient Technology, Beijing 100124, China a,b a b a CollegeofofGreen Architecture and Civil Engineering and, Beijing UniversityBeijing ofaaTechnology, Beijing, 100124, China Beijing Key Laboratory Built Environment and Energy Efficient Technology, University of Technology, Beijing, 100124, China a a,b a b a College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Beijing Key Laboratory of Green Built Environment and Energy Efficient Technology, Beijing University of Technology, Beijing, 100124, China b a Abstract College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Beijing Key Laboratory of Green Built Environment and Energy Efficient Technology, Beijing University of Technology, Beijing, 100124, China a b Beijing Key Laboratory Built Environment and Energy and, Efficient Technology, UniversityBeijing, of Technology, Beijing, 100124, China CollegeofofGreen Architecture and Civil Engineering Beijing UniversityBeijing of Technology, 100124, China a b Beijing Key Laboratory ofofGreen Built Environment and Energy and, Efficient Technology, UniversityBeijing, of Technology, Beijing, 100124, China College Architecture and Civil Engineering Beijing UniversityBeijing of Technology, 100124, China Abstract b scale coupling method which field model and network model are combined, the smoke spread in the underground Based on the multiCollege of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Abstract b College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China unidirectional tunnel was studied. We compared with the effect of smoke diffusion during different number of jet fans operated. Results
Yun-fei Yun-fei LI LI *, *, Yan-feng Yan-feng LI LI ,, Xiao Xiao FENG FENG ,, You-bo You-bo HUANG HUANG Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG
Abstract Based on the multicoupling which model and network model arewill combined, spread underground Abstract show that when threescale sets of fans aremethod operated, therefield is a backlayering of smoke which influencethe thesmoke simulation of in thethe model, thus we Based on the multiscale coupling method which field and network model are combined, the smoke spread in the underground Abstract unidirectional tunnelstate was of studied. We compared with themodel effect of of smoke diffusion during different number of jet fans operated. Results cannot get a steady smoke backlayering. When four sets jet fans are operated, the backlayering of smoke is eliminated, the Abstract Based on the multiscale couplingWe method which field model and network model are combined, the smokeofspread in operated. the underground unidirectional tunnel was studied. compared with the effect of smoke diffusion during different number jet fans Results show that when three sets of fans are operated, there is a backlayering of smoke which will influence the simulation of the model, thus we Abstract Based on the multiscale coupling method which field model and network model are combined, the smoke spread in the underground stratification in the downstream of fire. The result of simulation shows more reasonable. However, it is difficult to maintain a steady unidirectional tunnel was studied. We compared with the effect of smoke diffusion during different number of jet fans operated. Results show when threestate sets of of fans arebacklayering. operated, there is a backlayering of smoke will influence thesmoke simulation of in the model, thus the we Based on the multiscale coupling method which field model and network model are combined, the the underground cannotthat getthe a steady smoke When four sets of jet fans arewhich operated, the backlayering ofspread smoke is eliminated, unidirectional tunnel was studied. We compared with the effect of smoke diffusion during different number of jet fans operated. Results results of study can provide a reference for the design and operation of jet fans in the underground unidirectional tunnels. Based on the multiscale coupling method which field model andofnetwork model arewill combined, the the underground show that when threestate sets of of fans are operated, there isthe a backlayering of smoke influence thesmoke simulation of in the model, thus we cannot getsimulation a steady smoke backlayering. When four sets jet fans arewhich operated, the backlayering ofspread smoke is eliminated, the unidirectional tunnel was studied. We compared with effect of smoke diffusion during different number of jet fans operated. Results stratification in the downstream of fire. The result of shows more reasonable. However, it is difficult to maintain a steady Based on the multiscale coupling method which field model and network model are combined, the smoke spread in the underground show that when threestate sets of of smoke fans are operated, there isthe a backlayering of smoke will influence the simulation of the model, thus we unidirectional tunnel was studied. We compared with effect of of smoke diffusion during different number of fans operated. Results cannot getsimulation a steady backlayering. When four sets jet fans arewhich operated, the backlayering of jet smoke is eliminated, the stratification in the downstream of fire. The result of shows more reasonable. However, it is difficult to maintain a steady show that when three sets of fans are operated, there is a backlayering of smoke which will influence the simulation of the model, thus we results of the study can provide a reference for thewith design and operation offans jet fans in during the underground unidirectional tunnels. unidirectional tunnel was studied. We compared the effect of smoke diffusion different number of fans operated. Results cannot get a steady state of smoke backlayering. When four sets of jet arewhich operated, the backlayering of jet smoke is eliminated, the show that when three sets ofmore fans are operated, there isSelection a itbacklayering of smoke will influence the simulation of the model, thus we © 2017 The Authors. Published by Elsevier Ltd. and peer-review under responsibility of the Academic Committee stratification in the downstream of fire. The result of simulation shows reasonable. However, is difficult to maintain a steady results of the study can provide a reference for the design and operation of jet fans in the underground unidirectional tunnels. cannot get a steady state of smoke backlayering. When four sets of jet fans are operated, the backlayering of smoke is eliminated, the show that when threestate sets of ofmore fans are operated,However, there is a itbacklayering of will influence the simulation of the thusThe we stratification in the of fire. result of shows reasonable. is difficult toofsmoke maintain a the steady cannot getsimulation a steady smoke backlayering. When four sets of jet fans arewhich operated, the backlayering of downstream smoke is model, eliminated, the of ICFSFPE 2017. results of the study can provide a reference for the design and operation jet fans in underground unidirectional tunnels. stratification in of fire. The result of simulation shows reasonable. itfour is difficult tooffans maintain steady © 2017 The Authors. Published by Elsevier Selection responsibility of the the Academic Committee cannot get a steady state ofmore smoke backlayering. When setsand of peer-review jet are operated, the backlayering of downstream smoke is eliminated, the results of the study can provide a reference forHowever, theLtd. design and operation jet fans inaaunder the underground unidirectional tunnels. stratification in the downstream of fire. The result of simulation shows more reasonable. However, it is difficult to maintain steady © 2017 The Authors. Published by Elsevier Selection and peer-review responsibility of the thedownstream Academic results ofThe theAuthors. study can provide a reference forLtd. theLtd. design operation jet fans inaunder the underground unidirectional tunnels. Committee stratification in of fire. The result of simulation shows more reasonable. However, itand is method, difficult toof steady of ICFSFPE 2017. © 2018 Published by Elsevier results ofThe the can provide a reference forcoupling theLtd. design and operation ofmaintain jet fans inunder the underground tunnels. Committee Keywords: FDSstudy simulation, tunnel fire, multi-scale analysis exhausting, critical ventilationunidirectional velocity © 2017 Authors. Published by Elsevier Selection and smoke peer-review responsibility of the Academic of ICFSFPE 2017. results of the study can provide a reference for the design and operation of jet fans in the underground unidirectional tunnels. Committee Peer-review responsibility organizing ICFSFPE 2017.under responsibility of the Academic © 2017 Theunder Authors. PublishedofbytheElsevier Ltd.committee Selection of and peer-review
of 2017 ICFSFPE 2017. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Academic Committee © The Keywords: FDSAuthors. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity of 2017 ICFSFPE 2017. © The by Elsevier Ltd. analysis Selection and smoke peer-review under responsibility of the Academic Committee Keywords: FDSAuthors. simulation,Published tunnel fire, multi-scale coupling method, exhausting, critical ventilation velocity of ICFSFPE 2017. © 2017 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Academic Committee of Introduction ICFSFPE 1. Keywords: FDS 2017. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity of ICFSFPE Keywords: FDS 2017. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity Keywords: FDS simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity 1. Introduction Keywords: fire, multi-scale coupling tunnel analysis fire method, smoke exhausting, velocity Due toFDS thesimulation, confiningtunnel geometry of the tunnel, represents a major critical risk inventilation the event of fire. When a fire occurs in 1. Introduction Keywords: FDS simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity 1. Introduction a tunnel, the most hazardous factor is not flame and high temperature but toxic smoke. These large quantities of smoke are 1. Introduction Due to the confining geometry of the tunnel, tunnel fire represents a major risk in the event of fire. When a fire occurs in likely rapidly geometry along the of ceilingtunnel, of tunnel duefire to represents the confinement ofrisk theintunnel and of reduce visibility. Then, they Introduction Duetotospread themost confining abut major theThese event fire.quantities When a fire occurs in a1. tunnel, the hazardous factorofisthe nottunnel, flame tunnel and high temperature toxic smoke. large of smoke are 1. Introduction Due to the confining geometry the tunnel fire represents a major risk in the event of fire. When a fire occurs in become an obstacle to fire extinction and can cause deaths by asphyxiation alikely tunnel, the most hazardous factor is not flame and high temperature but toxic smoke. These large quantities of smoke are 1. Introduction rapidly alongfactor the of ceiling of tunnel due totemperature the confinement ofrisk the and large reduce visibility. they Duetotospread themost confining geometry tunnel, tunnel fire represents abut major intunnel theThese event of fire.quantities When a fire occurs in a tunnel, the hazardous isthe not flame and high toxic smoke. ofThen, smoke are [1-2] carried out a tunnel, series of small-scale experiments toofrisk examine the relationship between the critical Oka and Atkinson likely to spread rapidly along the ceiling of tunnel due to the confinement the tunnel and reduce visibility. Then, they Due to the confining geometry of the tunnel fire represents a major in the event of fire. When a fire occurs in become an obstacle to fire extinction and can cause deaths by asphyxiation alikely tunnel, the most hazardous factor is not flame and high temperature but toxic smoke. These large quantities of smoke are Due to the confining geometry of the tunnel, tunnel fire represents a major risk in the event of fire. When a fire occurs in to spread rapidly along the ceiling of tunnel due to the confinement of the tunnel and reduce visibility. Then, they velocity and the heat release rate, taking different geometries of the fire source into account. Wu and Bakar [3] carried out become an obstacle to fire extinction and can cause deaths by asphyxiation alikely tunnel, the most hazardous factor is not flame and high temperature but toxic smoke. These large quantities of smoke are Duetoto theAtkinson confining geometry the tunnel fire represents abut major intunnel thethe event of fire.quantities When a fire occurs in [1-2] carried out a tunnel, series of small-scale experiments toofrisk examine relationship between the critical Oka and spread rapidly along the of ceiling of tunnel due totemperature theasphyxiation confinement the and reduce visibility. Then, they aanother tunnel, the most hazardous factor is not flame and high toxic smoke. These large of smoke are become an obstacle to fire extinction and can cause deaths by series ofrapidly small-scale experimental insmall-scale five model tunnelsbut to toxic investigate the effect of tunnel geometry onthey the [1-2] carried out a series of experiments toofexamine the relationship between the critical Okatoand Atkinson spread along the taking ceiling oftests tunnel due to theasphyxiation confinement the tunnel and reduce visibility. Then, alikely tunnel, the most hazardous factor is not flame and high temperature smoke. These large quantities of smoke are velocity and the heat release rate, different geometries of the fire source into account. Wu and Bakar [3] carried out become an obstacle to fire extinction and can cause deaths by likely spread rapidly along thetunnels ceiling of tunnel dueheights to theexperiments confinement ofexamine the tunnel and reduce visibility. Then, they [1-2] carried out a series small-scale to thethe relationship between the critical Okato and Atkinson critical velocity, where the model had theofsame but widths. After study of Oka and[3]Atkinson [4velocity and theofrapidly heat rate, different of thedifferent firetosource intotunnel account. Wu Bakar carried out become an obstacle torelease fire extinction and can cause deaths by likely spread along the taking ceiling oftests tunnel due to theasphyxiation confinement the and reduce visibility. Then, another series small-scale experimental five model tunnels investigate the ofand tunnel geometry onthey the [1-2] carried out a series ofingeometries small-scale experiments toofexamine theeffect relationship between the critical Okatoand Atkinson become an obstacle to[6] fire extinction and can cause deaths by asphyxiation velocity and the heat release rate, taking different geometries of the fire source into account. Wu and Bakar [3] carried out carried out experimental study on the critical velocity to show how this was changed by the tunnel 5], Atkinson and Wu another series of small-scale experimental tests in five model tunnels to investigate the effect of tunnel geometry on the [1-2] carried out a series of small-scale experiments to examine the relationship between the critical Oka and Atkinson become an obstacle to fire extinction and can cause deaths by asphyxiation critical the model tunnels had theofin same but widths. study of Oka and [4velocity andAtkinson theofwhere heat release rate, taking different geometries thedifferent firetosource intoAfter account. Wuofand Bakar [3]Atkinson carried [1-2] carried out a series small-scale experiments to examine thethe relationship between the critical Oka velocity, and another series small-scale experimental tests fiveheights modelof tunnels investigate the effect tunnel geometry on out the slope. critical velocity, where the model tunnels had theofin same heights but widths. After the study of Oka and Atkinson [4velocity andAtkinson the heat release rate, taking different geometries of thedifferent fire source into account. Wuof and Bakar [3] carried out [1-2] carried out a series small-scale experiments to examine the relationship between the critical Oka and [6] carried out experimental study on the critical velocity to show how this was changed by the tunnel 5], Atkinson and Wu another series of small-scale experimental tests five model tunnels to investigate the effect tunnel geometry on the velocity and the heat release rate, taking different geometries of the fire source into account. Wu and Bakar [3] carried out critical velocity, where the model tunnels had thethe same heights but different widths. After the study of Oka and Atkinson [4A review of the state of the arts reveals that although aof number of investigations for the critical ventilation velocity [6] carried out experimental study on the critical velocity to show how this was changed by the tunnel 5], Atkinson and Wu another series of small-scale experimental tests in five model tunnels to investigate the effect of tunnel geometry on the velocity and the heat release rate, taking different geometries the fire source into account. Wu and Bakar [3] carried out slope. critical velocity, the model tunnels had the in same heights but different widths. After the study of Oka and Atkinson [4another series ofwhere small-scale experimental tests fivethere model tunnels to investigate the effect of tunnel geometry on the [6] carried out experimental study on the critical velocity to show how this was changed by the tunnel 5], Atkinson and Wu have been conducted. However, in the former studies are always few tunnel models built by a multi-scale numerical slope. critical velocity, where the model tunnels had the same heights but different widths. After the study of Oka and Atkinson [4another seriesof ofthe small-scale tests in five model tunnels to investigations investigate the effect of tunnel geometry on the A review state of theexperimental arts reveals that the although number of for the critical ventilation [6]the carried out experimental study on thea but critical velocity to show how this was changed by thevelocity tunnel 5], Atkinson and Wu critical velocity, where model tunnels had the same heights different widths. After the study of Oka and Atkinson [4slope. method, as a matter of fact it would help a lot in accuracy but take less time to calculate. Due to this fact, there is a need to A review of the state of the arts reveals that the although a number of investigations for the critical ventilation velocity [6] carried out experimental study on the critical velocity to show how this was changed by the tunnel 5], Atkinson and Wu critical velocity, where the modelout had the same heights but different widths. After the study of Oka and by Atkinson [4have been conducted. However, intunnels the former studies there are always fewinvestigations tunnel models built by a changed multi-scale numerical slope. [6] carried experimental study on the critical velocity to show how this was the tunnel 5], Atkinson and Wu A review of the state of the arts reveals that the although a number of for the critical ventilation velocity develop a reliable engineering tool based on theoretical analysis that canvelocity not only improve the accuracy but alsoby save time in have been conducted. However, in the former studies there are always few tunnel models built by a multi-scale numerical slope. [6] carried out experimental study on the critical to show how this was changed the tunnel 5], Atkinson and Wu method, as conducted. a of matter of However, fact helpformer a lot accuracy less of time to calculate. Due to critical thisa fact, there isnumerical avelocity need to A been review the state of itthewould arts reveals thatin the although atake number for the ventilation slope. have in the studies therebut are always fewinvestigations tunnel models built by multi-scale numerical simulation. method, asreliable a of matter of However, fact helpformer a lot in accuracy but less time to calculate. Due to critical thisa fact, there isnumerical avelocity need to A been review theengineering state of itthewould arts reveals that the although atake number of investigations for the ventilation slope. develop a tool based on theoretical analysis that can not only improve the accuracy but also save time in have conducted. in the studies there are always few tunnel models built by multi-scale A review of the state of the arts reveals that the although a number of investigations for the critical ventilation velocity method, ason a the matter of However, fact itthewould help a lot in accuracy but take less time to calculate. Due tocoupling thisa fact, there isis avelocity need to Based study of smoke flow informer the underground unidirectional tunnels, aimprove multi -for scale method adopted develop a reliable engineering tool based on theoretical analysis that can not only the accuracy but also save time in have been conducted. in the studies there are always few tunnel models built by multi-scale numerical A review of the state of arts reveals that the although a number of investigations the critical ventilation numerical simulation. method, asreliable a matter of However, fact it would helpformer a lot in accuracy but less time to calculate. Due to by thisa fact, there isnumerical a need to have been conducted. inbased the studies there aretake always few tunnel models built multi-scale develop a engineering tool on theoretical analysis that can not only improve the accuracy but also save time in in simulating the smoke exhausting effect by exerting the fire dynamics simulation software (FDS). The effect of smoke numerical simulation. method, ason a the matter of However, fact it would help a lot in accuracy but less time to calculate. Due tocoupling thisa fact, there isis a adopted need to have been conducted. inbased the former studies there aretake always few tunnel models built by multi-scale numerical Based study of smoke flow in the underground unidirectional tunnels, a multi scale method develop a reliable engineering tool on theoretical analysis that can not only improve the accuracy but also save time in method, as a matter of fact it would help a lot in accuracy but take less time to calculate. Due to this fact, there is a need to numerical simulation. exhausting and the smoke diffusion inhelp thethe tunnel are investigated so less that to decide amulti reasonable way offact, jet fans distribution. Basedaason the study of smoke flow in underground unidirectional tunnels, aimprove - Due scale coupling isof adopted develop reliable engineering tool based on theoretical analysis that can time notsimulation only the accuracy butmethod also save time in method, a matter of fact it would a lot in accuracy but take to calculate. to this there is a need to in simulating the smoke exhausting effect by exerting the fire dynamics software (FDS). The effect smoke numerical simulation. develop a reliable engineering tool based on theoretical analysis that can not only improve the accuracy but also save time in Baseda on the study of exhausting smoke flow in the underground tunnels, aimprove multi - the scale coupling method isofadopted in simulating the smoke effect by exerting theunidirectional fire that dynamics simulation software (FDS). The effect smoke numerical simulation. develop reliable engineering tool based on theoretical analysis can not only accuracy but also save time in exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. Based on the study of smoke flow in the underground unidirectional tunnels, a multi scale coupling method is adopted numerical simulation. in simulating the smoke by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke exhausting and the smoke diffusion ineffect thethe tunnel are investigated so that to decideaamulti reasonable of jet fans distribution. Based on the study of exhausting smoke flow in underground tunnels, - scaleway coupling method isof adopted numerical simulation. in simulating the smoke effect by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke Based on the study of exhausting smoke flow in the underground tunnels, aamulti - scaleway coupling method isofadopted exhausting and the smoke diffusion in the tunnel are investigated so that to decide reasonable of jet fans distribution. in simulating the smoke by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke Based onand the study of exhausting smoke flow in underground tunnels, - scaleway coupling method isof exhausting the smoke diffusion ineffect thethe tunnel are investigated so that to decideaamulti reasonable of jet fans distribution. in simulating the smoke exhausting effect by exerting the fire dynamics simulation software (FDS). The effect ofadopted smoke exhausting andauthor. thesmoke smoke diffusion ineffect the tunnel are investigated so that to simulation decide a reasonable way of jet fans distribution. * Corresponding Tel.:+86-188-1151-9527. in simulating the exhausting by exerting the fire dynamics software (FDS). The effect of smoke exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. E-mail address:[email protected] exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. * Corresponding author. Tel.:+86-188-1151-9527. * Corresponding author. Tel.:+86-188-1151-9527. 1877-7058 © 2018 The Authors. Published by Elsevier Ltd. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] Peer-review under responsibility of the organizing committee of ICFSFPE 2017 * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] 10.1016/j.proeng.2017.12.031 * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] E-mail address:[email protected]
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2. FDS calculation model and fire scene FDS is a fluid dynamics program developed by NIST (National Institute of Standards and Technology). The program can be used to for fire related problems, such as smoke spreading and so on. There are two main methods used in the simulation, simulate directly and large eddy simulation. FDS solves flow equations numerically. The physical equations include NavierStokes equations for flow analysis, energy conservation equations for temperature distribution and other scalar equation for smoke and particulates transport. Governing equations are described as follows: Conservation of mass, Conservation of momentum, Conversation of momentum, Conversation of energy, Conversation of species. Predicted FDS results for near fire field agreed fairly well with the experiments. It shows that the numerical simulation can truly reflect the smoke spread in the tunnel when the fire occurred. 2.1. Tunnel model The model is a 1.2 km underground road. The structure of the model represents a typical unidirectional tunnel. Tunnel height is 6.5 m with a standard horseshoe section. The cross-sectional area is 53 m2 and hydraulic diameter is 7.3m. Five pairs of jet fans were placed in the tunnel inlet and outlet by two groups. The flow rate of a single jet fan is 8.9 m3/s and the ventilation velocity is 34 m/s at jet fan outlet. A steady-state fire source with heat release rate(HRR) 30 MW is located in the middle of the tunnel.
Fig. 1 multi-scale coupled simulation model
As shown in Fig.1, a multi-scale coupled simulation model was established with FDS6. In order to observe the maximum length of the smoke backlayering, according to the previous experience, the 1200 m tunnel is divided into 400 m upstream for 1D model, 400 m including fire source for 3D model and 400 m downstream for 1D model. The flow measuring points are set at 10 m from inlet and outlet of 3D zone respectively to measure changes in the amount of air flow in the tunnel. 2.2. Grid system The thermal parameters such as temperature and mass concentration are relatively large near the fire source [7-8]. Therefore, grid encryption is carried out near the fire source, and the sparse grid is adopted away from the fire source due to the smaller thermal physics gradient. The NIST test shows that the simulation results are in good agreement with the experimental results when the grid size is 1/10 of the characteristic size D * of the fire source [9-10]. When the fire source is located at 202-208 m, 160-240 m is divided by 0.25 m × 0.25 m grid cell. The remaining area is divided by 0.5 m × 0.5 m grid cell and the total number of grid cells is 518400. The grids are equally divided into 12 sub-grids in order to reduce the simulation time by using the FDS parallel computing function. 2.3. Boundary conditions and simulation conditions Both sides of the underground channel are mechanical ventilation outlet boundary. The ambient temperature is 20 ℃. Due to the semi-closed nature of the tunnel, the tunnel wall is set to adiabatic surface. In order to investigate the effect of the number of jet fans on the smoke spread, the simulation is based on the multi-scale coupling analysis. 3. FDS simulation method for multi-scale coupling analysis 3.1. 3D CFD simulation Method for jet fan and fire source area The 3D model is carried out in the area which contains the fire source, and the rest is modelled in 1D form. We combine the 1D and 3D area together in the simulation. This method make it possible to accomplish multi-scale coupling analysis of the whole tunnel. There is a high temperature gradient in the area where the fire source is located and a high velocity gradient in the area where the jet fans are located, the 3D model is adopted in these two areas. The evolution of the smoke flow by using this method is closest to the real situation. However, it takes too long time to reflect the advantages of multi-
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scale coupling analysis. In view of the fact that it takes a long time when the 3D model is adopted in both areas where jet fans and fire sources are located. An equivalent method is selected. We only build 3D model in the fire source area and equalize external effect of jet fans into the 1D model with single fan in both sides of the tunnel. This method greatly shortens the simulation time. The air volume of the fan in the 1D model varies according to the quadratic curve given by equation (1), since the pressure difference between both sides of 1D model is proportional to the square of the air volume.
̇ ∆𝑃𝑃 −∆𝑝𝑝 𝑉𝑉𝑓𝑓𝑓𝑓𝑓𝑓 = 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑖𝑖̇𝑔𝑔𝑔𝑔(∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 − ∆𝑝𝑝)√ 𝑚𝑚𝑚𝑚𝑚𝑚 ∆𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚
(1)
Among them, 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum air volume that jet fan can provide during the time when there is no pressure at both sides of the 1D model, ∆P = 𝑃𝑃1 − 𝑃𝑃2 represent the pressure difference between the 3D area and the upstream of 1D model, subscript 1 and 2 are on behave of the downstream and the upstream respectively. ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum pressure difference that the fan can work with. The air volume of the fan will drop from 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 to 0 m3/s with the process that pressure difference. rise from 0 to ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 . If the pressure difference exceed with the maximum value, the air flow will be forced to reverse. In the coupling simulation, we get the value of 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 by using IDA-RTV iteration in the condition of jet fans operated when there is no fire source in the tunnel. The value of ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 in the equation (2) is the maximum of one jet fan can provide multiplied by the number of fans.
∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 = 𝑛𝑛 lim 𝑉𝑉𝑗𝑗2 𝑣𝑣𝑖𝑖 →0
𝐴𝐴𝑗𝑗
𝐴𝐴𝑟𝑟
4. FDS simulation method for multi-scale coupling analysis
(1 −
𝑉𝑉𝑟𝑟 ) 𝜂𝜂 𝑉𝑉𝐽𝐽
（2）
4.1. Simulated operating conditions and equivalent fan initial air volume In a 30 MW fire scenario, the critical ventilation velocity of the tunnel was 3.81 m /s according to the empirical formula of Wu [5]. When there is no fire, the ventilation velocity in the tunnel was 4.07 m / s by using IDA-RTV iteration when only 3 sets of jet fan were operated in the upstream of fire. If 4 sets of jet fan were operated in the upstream of fire, the ventilation velocity would be 4.66 m/s. We selected these two cases where the ventilation velocity is higher than the critical value as researched objects.
Fig. 2 1D-3D Coupling interface sketch
The 1D-3D coupling interface was set as the full cross-section of the tunnel, as shown in Fig.2. And the quadratic flow model was simulated when there was no the fire source. It was found that the air volume was not the designed maximum air volume at the beginning of the simulation, the air volume increased gradually. However, the application of the secondary air volume curve model cannot simulate the fire field flow field evolution process, we can only get a steady state 2 min after the initial air volume change. According to the analysis of the result, we will combine the SmokeView with the air volume measurement point and the smoke visualization diagram obtained by volume rendering of the soot concentration in the grid to judge whether the flow field is stable.
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4.2. Open 3 sets of fans in the upstream of fire
Fig. 3 smoke propagation varies with time while 3 fans operating
As shown in Fig.3, the smoke spread to upstream then inverted back. It inverted to the minimum backlayering length at 254 s and only lasted a short time, and then spread to the upstream of the fire until the coupling interface. Fig.4 shows that air volume decreased to 80 m3 / s at 280 s and then fluctuated slightly at about 65 m3 / s in the upstream inlet.
Fig. 4 the curve of the upstream air volume in the three fans opening condition
When the smoke inverted to the position of the minimum backlayering, we got the temperature and velocity distribution near the fire source. The reason was that the backlayering of smoke affected the process of simulation in FDS. Finally, the air volume of the equivalent fan was declined and the smoke spread to the upstream. The burning model used a simple chemistry model. When the ventilation velocity was low, the backlayering of the smoke changed the oxygen concentration acutely in the fire source area which resulted in the chemical reaction could not keep in a steady state. In addition, the soot in the backlayering of smoke affected the radiational heat transfer process, thus changed the ratio of radiation and the convection in total heat release. In the coupled simulation, the fire source was simulated by a more complicated model, and the backlayering of the smoke affected the simulation of fire source, this resulted in an unsteady state of the smoke. At present, there is only one way to simulate a stable backlayering of smoke by using the simplest volume of heat source to represent the fire source. However, when using FDS contained burning model, even if the inlet boundary condition was set as smaller ventilation velocity, the length of backlayering may also inaccurate. 4.3. Open 4 sets of fans in the upstream of fire When opened 4 sets of jet fans in the upstream of fire, the ventilation velocity in the tunnel reached 4.66 m / s, and the process of smoke spread after the velocity increased is shown in Fig. 5. Smoke spread to the upstream of the fire for a distance during the initial air volume was rose by the equivalent fan. But it began to fall back at 90 s and there is no backlayering of smoke until to 210 s. According to the previous analysis, the fire source burning was not stable before 210 s. Based on the temperature distribution near the fire source, it can be seen that there is no backlayering after 210 s, and the burning of the fire source was relatively stable. The velocity distribution in the upstream of the fire source is uniform, and the turbulence in the downstream of the fire was strong, which destroyed the smoke layer absolutely. So when the
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ventilation velocity was larger than the critical value, the downstream of smoke was difficult to maintain a stable stratification.
Fig.5 smoke propagation varies with time while 4 fans opening
In the larger ventilation velocity, we can get a reasonable result of simulation. As shown in fig.6. the air volume in the tunnel became relatively stable after 300 s. For the 3D area, the difference of air volume at the inlet and outlet was about 35 m3/s. And based on the steady value of the air volume at inlet, we could get the pressure loss by combining with the quadratic curve of equivalent fan.
Fig. 6 the curve of the upstream air volume in the four fans opening condition
5. Conclusion In this study, a multi-scale coupling method is adopted in simulating the smoke exhausting effect by exerting the fire dynamics simulation software (FDS). The conclusions are drawn as follows: (1) When operating 3 sets of fans, due to the smaller ventilation velocity, backlayering of smoke would appear the upstream of fire. Because fire source treatment should be adopted a more complex model, a stable backlayering is difficult to be simulated. (2) When operating 4 sets of fans, the backlayering of smoke was eliminated by larger ventilation velocity, the result of simulation was good. Under this condition, the turbulence in the downstream of the fire source is very strong, which completely destroyed the smoke layer. So when the ventilation velocity is larger than critical value, it is difficult to maintain stable stratification in the downstream of fire. (3)After reaching the steady state, and based on the steady value of the air volume at inlet, we can get the pressure loss by combination with the quadratic curve of equivalent fan.
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Acknowledgements This work was supported by Beijing Natural Science Foundation (Grant No: 8172006) and Natural Science Foundation of China (Grant No: 51278018) References [1] Lee C K, Chaiken R F, J.M.Singer. Interaction between duct fires and ventilation flow: an experimental study, Journal of Combustion Science and Technology 2014, 20(4): 59-72. [2] Carvel R O, Beard A N, Jowitt P W. The influence of tunnel geometry and ventilation on the heat release rate of fire[J]. Fire Technology, 2004, 40(1): 5-26． [3] Cheng X H, Zeng Y H, He C, et al. Study on flow resistance in tunnel fire zone, Journal of the China Railway Society 2011, 29(2): 133-136． [4] Wang M N, Yang Q X, Yuan X K, et al. The model test on ventilation pressure change in highway tunnel fire, Journal of Highway and Transportation Research and Development, 2015, 21(3): 60-63． [5] Dutrieue R, Jacques E. Pressure loss caused by fire in a tunnel. Proceedings of the 12th International Symposium on Aerodynamics and Ventilation of Vehicle Tunnels. Portoroz : BHR Group, 2012, 30(6): 77-84． [6] Vauquelin O, Megret O. Smoke extraction experiments in case of fire in a tunnel[J]. Fire Safety Journal, 2002, 37(5): 525-533． [7] Liu Q, Jiang X P, Cai C Q. The multi-objective decision-making analysis of the intensive tunnel exhaust port [J]. Journal of Safety and Environment, 2013, 18(02): 214-218. [8] Carvel R O, Beard A N, Jowitt P W. The influence of longitudinal ventilation systems of fires in tunnels[J]. Tunnelling and Underground Technology， 2001, 30(9): 3-21. [9] Mcgrattan K, Hostikka S, Mceta L. 2014. NIST special publication 1018-6: fire dynamics simulator technical reference guide volume 3: validation, Gaithersburg: National Institute of Standards and Technology． [10] Wu Y, Baker, Mz A. Control of smoke flow in tunnel fires using longitudinal ventilation systems-a study of the critical velocity, Fire Safety Journal 2015, 36(8): 363-390．
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Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering00 211 (2018) 421–426 Procedia Engineering (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000
Influence of Arrangement of Jet Fans on Smoke Exhaust Effect in a Influence of Arrangement of Fans on Smoke Exhaust Effect with Longitudinal Ventilation System 2017 8th International Conference on Fire Science Fire Protection Engineering Influence ofTunnel Arrangement of Jet Jet Fans onand Smoke Exhaust Effect in in aa Influence of Arrangement of Jet Fans on Smoke Effect in a Tunnel Longitudinal Ventilation System (on theawith Development ofa,bPerformance-based Fire Exhaust Code) Influence of Arrangement of Jet Fans on Smoke Exhaust a a Effect in a Tunnel with Longitudinal Ventilation System Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG Influence of Arrangement of Jet Fans on Smoke Exhaust Effect Tunnel with Longitudinal System Influence of Arrangement of Jet FansVentilation on Smoke Exhaust Effect in in aa awith Longitudinal a,b FansVentilation a a Effect in a Tunnel System Influence of Arrangement of Jet on Smoke Exhaust Yun-fei LI *, Yan-feng LIa,b , Xiao FENG HUANG a, You-bo a Tunnel Longitudinal Ventilation Beijing Key Laboratory of Green LI Builtawith Environment and Energy Efficient Technology, Beijing University ofSystem Technology, Beijing, 100124, China Yun-fei *, Yan-feng LIa,b , Xiao FENG , You-bo HUANG Tunnel Ventilation System awith Longitudinal a a Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG Tunnel with Longitudinal Ventilation System College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China a a,b a a Beijing Key Laboratory of Green LI Built *, Environment and Energy Technology, Beijing University of HUANG Technology, Beijing, 100124, China Yun-fei Yan-feng LI Efficient , Xiao FENG , You-bo a a a
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a University of Technology, Beijing, a Beijing Key Laboratory of Green Builtaa Environment and Energya,b Efficient Technology, Beijing 100124, China a,b a b a CollegeofofGreen Architecture and Civil Engineering and, Beijing UniversityBeijing ofaaTechnology, Beijing, 100124, China Beijing Key Laboratory Built Environment and Energy Efficient Technology, University of Technology, Beijing, 100124, China a a,b a b a College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Beijing Key Laboratory of Green Built Environment and Energy Efficient Technology, Beijing University of Technology, Beijing, 100124, China b a Abstract College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Beijing Key Laboratory of Green Built Environment and Energy Efficient Technology, Beijing University of Technology, Beijing, 100124, China a b Beijing Key Laboratory Built Environment and Energy and, Efficient Technology, UniversityBeijing, of Technology, Beijing, 100124, China CollegeofofGreen Architecture and Civil Engineering Beijing UniversityBeijing of Technology, 100124, China a b Beijing Key Laboratory ofofGreen Built Environment and Energy and, Efficient Technology, UniversityBeijing, of Technology, Beijing, 100124, China College Architecture and Civil Engineering Beijing UniversityBeijing of Technology, 100124, China Abstract b scale coupling method which field model and network model are combined, the smoke spread in the underground Based on the multiCollege of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China Abstract b College of Architecture and Civil Engineering and, Beijing University of Technology, Beijing, 100124, China unidirectional tunnel was studied. We compared with the effect of smoke diffusion during different number of jet fans operated. Results
Yun-fei Yun-fei LI LI *, *, Yan-feng Yan-feng LI LI ,, Xiao Xiao FENG FENG ,, You-bo You-bo HUANG HUANG Yun-fei LI *, Yan-feng LI , Xiao FENG , You-bo HUANG
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When four sets jet fans are operated, the backlayering of smoke is eliminated, the Abstract Based on the multiscale couplingWe method which field model and network model are combined, the smokeofspread in operated. the underground unidirectional tunnel was studied. compared with the effect of smoke diffusion during different number jet fans Results show that when three sets of fans are operated, there is a backlayering of smoke which will influence the simulation of the model, thus we Abstract Based on the multiscale coupling method which field model and network model are combined, the smoke spread in the underground stratification in the downstream of fire. The result of simulation shows more reasonable. However, it is difficult to maintain a steady unidirectional tunnel was studied. We compared with the effect of smoke diffusion during different number of jet fans operated. 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However, it is difficult to maintain a steady show that when three sets of fans are operated, there is a backlayering of smoke which will influence the simulation of the model, thus we results of the study can provide a reference for thewith design and operation offans jet fans in during the underground unidirectional tunnels. unidirectional tunnel was studied. We compared the effect of smoke diffusion different number of fans operated. Results cannot get a steady state of smoke backlayering. When four sets of jet arewhich operated, the backlayering of jet smoke is eliminated, the show that when three sets ofmore fans are operated, there isSelection a itbacklayering of smoke will influence the simulation of the model, thus we © 2017 The Authors. Published by Elsevier Ltd. and peer-review under responsibility of the Academic Committee stratification in the downstream of fire. The result of simulation shows reasonable. However, is difficult to maintain a steady results of the study can provide a reference for the design and operation of jet fans in the underground unidirectional tunnels. cannot get a steady state of smoke backlayering. When four sets of jet fans are operated, the backlayering of smoke is eliminated, the show that when threestate sets of ofmore fans are operated,However, there is a itbacklayering of will influence the simulation of the thusThe we stratification in the of fire. result of shows reasonable. is difficult toofsmoke maintain a the steady cannot getsimulation a steady smoke backlayering. When four sets of jet fans arewhich operated, the backlayering of downstream smoke is model, eliminated, the of ICFSFPE 2017. results of the study can provide a reference for the design and operation jet fans in underground unidirectional tunnels. stratification in of fire. The result of simulation shows reasonable. itfour is difficult tooffans maintain steady © 2017 The Authors. Published by Elsevier Selection responsibility of the the Academic Committee cannot get a steady state ofmore smoke backlayering. When setsand of peer-review jet are operated, the backlayering of downstream smoke is eliminated, the results of the study can provide a reference forHowever, theLtd. design and operation jet fans inaaunder the underground unidirectional tunnels. stratification in the downstream of fire. The result of simulation shows more reasonable. However, it is difficult to maintain steady © 2017 The Authors. Published by Elsevier Selection and peer-review responsibility of the thedownstream Academic results ofThe theAuthors. study can provide a reference forLtd. theLtd. design operation jet fans inaunder the underground unidirectional tunnels. Committee stratification in of fire. The result of simulation shows more reasonable. 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of 2017 ICFSFPE 2017. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Academic Committee © The Keywords: FDSAuthors. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity of 2017 ICFSFPE 2017. © The by Elsevier Ltd. analysis Selection and smoke peer-review under responsibility of the Academic Committee Keywords: FDSAuthors. simulation,Published tunnel fire, multi-scale coupling method, exhausting, critical ventilation velocity of ICFSFPE 2017. © 2017 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Academic Committee of Introduction ICFSFPE 1. Keywords: FDS 2017. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity of ICFSFPE Keywords: FDS 2017. simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity Keywords: FDS simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity 1. Introduction Keywords: fire, multi-scale coupling tunnel analysis fire method, smoke exhausting, velocity Due toFDS thesimulation, confiningtunnel geometry of the tunnel, represents a major critical risk inventilation the event of fire. When a fire occurs in 1. Introduction Keywords: FDS simulation, tunnel fire, multi-scale coupling analysis method, smoke exhausting, critical ventilation velocity 1. Introduction a tunnel, the most hazardous factor is not flame and high temperature but toxic smoke. These large quantities of smoke are 1. 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The effect smoke numerical simulation. develop reliable engineering tool based on theoretical analysis can not only accuracy but also save time in exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. Based on the study of smoke flow in the underground unidirectional tunnels, a multi scale coupling method is adopted numerical simulation. in simulating the smoke by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke exhausting and the smoke diffusion ineffect thethe tunnel are investigated so that to decideaamulti reasonable of jet fans distribution. Based on the study of exhausting smoke flow in underground tunnels, - scaleway coupling method isof adopted numerical simulation. in simulating the smoke effect by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke Based on the study of exhausting smoke flow in the underground tunnels, aamulti - scaleway coupling method isofadopted exhausting and the smoke diffusion in the tunnel are investigated so that to decide reasonable of jet fans distribution. in simulating the smoke by exerting theunidirectional fire dynamics simulation software (FDS). The effect smoke Based onand the study of exhausting smoke flow in underground tunnels, - scaleway coupling method isof exhausting the smoke diffusion ineffect thethe tunnel are investigated so that to decideaamulti reasonable of jet fans distribution. in simulating the smoke exhausting effect by exerting the fire dynamics simulation software (FDS). The effect ofadopted smoke exhausting andauthor. thesmoke smoke diffusion ineffect the tunnel are investigated so that to simulation decide a reasonable way of jet fans distribution. * Corresponding Tel.:+86-188-1151-9527. in simulating the exhausting by exerting the fire dynamics software (FDS). The effect of smoke exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. E-mail address:[email protected] exhausting and the smoke diffusion in the tunnel are investigated so that to decide a reasonable way of jet fans distribution. * Corresponding author. Tel.:+86-188-1151-9527. * Corresponding author. Tel.:+86-188-1151-9527. 1877-7058 © 2018 The Authors. Published by Elsevier Ltd. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] Peer-review under responsibility of the organizing committee of ICFSFPE 2017 * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] 10.1016/j.proeng.2017.12.031 * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] * Corresponding author. Tel.:+86-188-1151-9527. E-mail address:[email protected] E-mail address:[email protected]
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2. FDS calculation model and fire scene FDS is a fluid dynamics program developed by NIST (National Institute of Standards and Technology). The program can be used to for fire related problems, such as smoke spreading and so on. There are two main methods used in the simulation, simulate directly and large eddy simulation. FDS solves flow equations numerically. The physical equations include NavierStokes equations for flow analysis, energy conservation equations for temperature distribution and other scalar equation for smoke and particulates transport. Governing equations are described as follows: Conservation of mass, Conservation of momentum, Conversation of momentum, Conversation of energy, Conversation of species. Predicted FDS results for near fire field agreed fairly well with the experiments. It shows that the numerical simulation can truly reflect the smoke spread in the tunnel when the fire occurred. 2.1. Tunnel model The model is a 1.2 km underground road. The structure of the model represents a typical unidirectional tunnel. Tunnel height is 6.5 m with a standard horseshoe section. The cross-sectional area is 53 m2 and hydraulic diameter is 7.3m. Five pairs of jet fans were placed in the tunnel inlet and outlet by two groups. The flow rate of a single jet fan is 8.9 m3/s and the ventilation velocity is 34 m/s at jet fan outlet. A steady-state fire source with heat release rate(HRR) 30 MW is located in the middle of the tunnel.
Fig. 1 multi-scale coupled simulation model
As shown in Fig.1, a multi-scale coupled simulation model was established with FDS6. In order to observe the maximum length of the smoke backlayering, according to the previous experience, the 1200 m tunnel is divided into 400 m upstream for 1D model, 400 m including fire source for 3D model and 400 m downstream for 1D model. The flow measuring points are set at 10 m from inlet and outlet of 3D zone respectively to measure changes in the amount of air flow in the tunnel. 2.2. Grid system The thermal parameters such as temperature and mass concentration are relatively large near the fire source [7-8]. Therefore, grid encryption is carried out near the fire source, and the sparse grid is adopted away from the fire source due to the smaller thermal physics gradient. The NIST test shows that the simulation results are in good agreement with the experimental results when the grid size is 1/10 of the characteristic size D * of the fire source [9-10]. When the fire source is located at 202-208 m, 160-240 m is divided by 0.25 m × 0.25 m grid cell. The remaining area is divided by 0.5 m × 0.5 m grid cell and the total number of grid cells is 518400. The grids are equally divided into 12 sub-grids in order to reduce the simulation time by using the FDS parallel computing function. 2.3. Boundary conditions and simulation conditions Both sides of the underground channel are mechanical ventilation outlet boundary. The ambient temperature is 20 ℃. Due to the semi-closed nature of the tunnel, the tunnel wall is set to adiabatic surface. In order to investigate the effect of the number of jet fans on the smoke spread, the simulation is based on the multi-scale coupling analysis. 3. FDS simulation method for multi-scale coupling analysis 3.1. 3D CFD simulation Method for jet fan and fire source area The 3D model is carried out in the area which contains the fire source, and the rest is modelled in 1D form. We combine the 1D and 3D area together in the simulation. This method make it possible to accomplish multi-scale coupling analysis of the whole tunnel. There is a high temperature gradient in the area where the fire source is located and a high velocity gradient in the area where the jet fans are located, the 3D model is adopted in these two areas. The evolution of the smoke flow by using this method is closest to the real situation. However, it takes too long time to reflect the advantages of multi-
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scale coupling analysis. In view of the fact that it takes a long time when the 3D model is adopted in both areas where jet fans and fire sources are located. An equivalent method is selected. We only build 3D model in the fire source area and equalize external effect of jet fans into the 1D model with single fan in both sides of the tunnel. This method greatly shortens the simulation time. The air volume of the fan in the 1D model varies according to the quadratic curve given by equation (1), since the pressure difference between both sides of 1D model is proportional to the square of the air volume.
̇ ∆𝑃𝑃 −∆𝑝𝑝 𝑉𝑉𝑓𝑓𝑓𝑓𝑓𝑓 = 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 𝑠𝑠𝑖𝑖̇𝑔𝑔𝑔𝑔(∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 − ∆𝑝𝑝)√ 𝑚𝑚𝑚𝑚𝑚𝑚 ∆𝑝𝑝𝑚𝑚𝑚𝑚𝑚𝑚
(1)
Among them, 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum air volume that jet fan can provide during the time when there is no pressure at both sides of the 1D model, ∆P = 𝑃𝑃1 − 𝑃𝑃2 represent the pressure difference between the 3D area and the upstream of 1D model, subscript 1 and 2 are on behave of the downstream and the upstream respectively. ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 is the maximum pressure difference that the fan can work with. The air volume of the fan will drop from 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 to 0 m3/s with the process that pressure difference. rise from 0 to ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 . If the pressure difference exceed with the maximum value, the air flow will be forced to reverse. In the coupling simulation, we get the value of 𝑉𝑉𝑚𝑚𝑚𝑚𝑚𝑚 by using IDA-RTV iteration in the condition of jet fans operated when there is no fire source in the tunnel. The value of ∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 in the equation (2) is the maximum of one jet fan can provide multiplied by the number of fans.
∆𝑃𝑃𝑚𝑚𝑚𝑚𝑚𝑚 = 𝑛𝑛 lim 𝑉𝑉𝑗𝑗2 𝑣𝑣𝑖𝑖 →0
𝐴𝐴𝑗𝑗
𝐴𝐴𝑟𝑟
4. FDS simulation method for multi-scale coupling analysis
(1 −
𝑉𝑉𝑟𝑟 ) 𝜂𝜂 𝑉𝑉𝐽𝐽
（2）
4.1. Simulated operating conditions and equivalent fan initial air volume In a 30 MW fire scenario, the critical ventilation velocity of the tunnel was 3.81 m /s according to the empirical formula of Wu [5]. When there is no fire, the ventilation velocity in the tunnel was 4.07 m / s by using IDA-RTV iteration when only 3 sets of jet fan were operated in the upstream of fire. If 4 sets of jet fan were operated in the upstream of fire, the ventilation velocity would be 4.66 m/s. We selected these two cases where the ventilation velocity is higher than the critical value as researched objects.
Fig. 2 1D-3D Coupling interface sketch
The 1D-3D coupling interface was set as the full cross-section of the tunnel, as shown in Fig.2. And the quadratic flow model was simulated when there was no the fire source. It was found that the air volume was not the designed maximum air volume at the beginning of the simulation, the air volume increased gradually. However, the application of the secondary air volume curve model cannot simulate the fire field flow field evolution process, we can only get a steady state 2 min after the initial air volume change. According to the analysis of the result, we will combine the SmokeView with the air volume measurement point and the smoke visualization diagram obtained by volume rendering of the soot concentration in the grid to judge whether the flow field is stable.
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4.2. Open 3 sets of fans in the upstream of fire
Fig. 3 smoke propagation varies with time while 3 fans operating
As shown in Fig.3, the smoke spread to upstream then inverted back. It inverted to the minimum backlayering length at 254 s and only lasted a short time, and then spread to the upstream of the fire until the coupling interface. Fig.4 shows that air volume decreased to 80 m3 / s at 280 s and then fluctuated slightly at about 65 m3 / s in the upstream inlet.
Fig. 4 the curve of the upstream air volume in the three fans opening condition
When the smoke inverted to the position of the minimum backlayering, we got the temperature and velocity distribution near the fire source. The reason was that the backlayering of smoke affected the process of simulation in FDS. Finally, the air volume of the equivalent fan was declined and the smoke spread to the upstream. The burning model used a simple chemistry model. When the ventilation velocity was low, the backlayering of the smoke changed the oxygen concentration acutely in the fire source area which resulted in the chemical reaction could not keep in a steady state. In addition, the soot in the backlayering of smoke affected the radiational heat transfer process, thus changed the ratio of radiation and the convection in total heat release. In the coupled simulation, the fire source was simulated by a more complicated model, and the backlayering of the smoke affected the simulation of fire source, this resulted in an unsteady state of the smoke. At present, there is only one way to simulate a stable backlayering of smoke by using the simplest volume of heat source to represent the fire source. However, when using FDS contained burning model, even if the inlet boundary condition was set as smaller ventilation velocity, the length of backlayering may also inaccurate. 4.3. Open 4 sets of fans in the upstream of fire When opened 4 sets of jet fans in the upstream of fire, the ventilation velocity in the tunnel reached 4.66 m / s, and the process of smoke spread after the velocity increased is shown in Fig. 5. Smoke spread to the upstream of the fire for a distance during the initial air volume was rose by the equivalent fan. But it began to fall back at 90 s and there is no backlayering of smoke until to 210 s. According to the previous analysis, the fire source burning was not stable before 210 s. Based on the temperature distribution near the fire source, it can be seen that there is no backlayering after 210 s, and the burning of the fire source was relatively stable. The velocity distribution in the upstream of the fire source is uniform, and the turbulence in the downstream of the fire was strong, which destroyed the smoke layer absolutely. So when the
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ventilation velocity was larger than the critical value, the downstream of smoke was difficult to maintain a stable stratification.
Fig.5 smoke propagation varies with time while 4 fans opening
In the larger ventilation velocity, we can get a reasonable result of simulation. As shown in fig.6. the air volume in the tunnel became relatively stable after 300 s. For the 3D area, the difference of air volume at the inlet and outlet was about 35 m3/s. And based on the steady value of the air volume at inlet, we could get the pressure loss by combining with the quadratic curve of equivalent fan.
Fig. 6 the curve of the upstream air volume in the four fans opening condition
5. Conclusion In this study, a multi-scale coupling method is adopted in simulating the smoke exhausting effect by exerting the fire dynamics simulation software (FDS). The conclusions are drawn as follows: (1) When operating 3 sets of fans, due to the smaller ventilation velocity, backlayering of smoke would appear the upstream of fire. Because fire source treatment should be adopted a more complex model, a stable backlayering is difficult to be simulated. (2) When operating 4 sets of fans, the backlayering of smoke was eliminated by larger ventilation velocity, the result of simulation was good. Under this condition, the turbulence in the downstream of the fire source is very strong, which completely destroyed the smoke layer. So when the ventilation velocity is larger than critical value, it is difficult to maintain stable stratification in the downstream of fire. (3)After reaching the steady state, and based on the steady value of the air volume at inlet, we can get the pressure loss by combination with the quadratic curve of equivalent fan.
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Acknowledgements This work was supported by Beijing Natural Science Foundation (Grant No: 8172006) and Natural Science Foundation of China (Grant No: 51278018) References [1] Lee C K, Chaiken R F, J.M.Singer. Interaction between duct fires and ventilation flow: an experimental study, Journal of Combustion Science and Technology 2014, 20(4): 59-72. [2] Carvel R O, Beard A N, Jowitt P W. The influence of tunnel geometry and ventilation on the heat release rate of fire[J]. Fire Technology, 2004, 40(1): 5-26． [3] Cheng X H, Zeng Y H, He C, et al. Study on flow resistance in tunnel fire zone, Journal of the China Railway Society 2011, 29(2): 133-136． [4] Wang M N, Yang Q X, Yuan X K, et al. The model test on ventilation pressure change in highway tunnel fire, Journal of Highway and Transportation Research and Development, 2015, 21(3): 60-63． [5] Dutrieue R, Jacques E. Pressure loss caused by fire in a tunnel. Proceedings of the 12th International Symposium on Aerodynamics and Ventilation of Vehicle Tunnels. Portoroz : BHR Group, 2012, 30(6): 77-84． [6] Vauquelin O, Megret O. Smoke extraction experiments in case of fire in a tunnel[J]. Fire Safety Journal, 2002, 37(5): 525-533． [7] Liu Q, Jiang X P, Cai C Q. The multi-objective decision-making analysis of the intensive tunnel exhaust port [J]. Journal of Safety and Environment, 2013, 18(02): 214-218. [8] Carvel R O, Beard A N, Jowitt P W. The influence of longitudinal ventilation systems of fires in tunnels[J]. Tunnelling and Underground Technology， 2001, 30(9): 3-21. [9] Mcgrattan K, Hostikka S, Mceta L. 2014. NIST special publication 1018-6: fire dynamics simulator technical reference guide volume 3: validation, Gaithersburg: National Institute of Standards and Technology． [10] Wu Y, Baker, Mz A. Control of smoke flow in tunnel fires using longitudinal ventilation systems-a study of the critical velocity, Fire Safety Journal 2015, 36(8): 363-390．