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Fire Development in An Underground Corridor — Studies on Ceiling-jet Flow and Flashover Mechanism Mr. Songyang Li STATE KEY LABORATORY OF FIRE SCIENCE,

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Presentation on theme: "Fire Development in An Underground Corridor — Studies on Ceiling-jet Flow and Flashover Mechanism Mr. Songyang Li STATE KEY LABORATORY OF FIRE SCIENCE,"— Presentation transcript:

1 Fire Development in An Underground Corridor — Studies on Ceiling-jet Flow and Flashover Mechanism Mr. Songyang Li STATE KEY LABORATORY OF FIRE SCIENCE, China Dept. of Energy Sciences, Lund University, Sweden

2 STATE KEY LABORATORY OF FIRE SCIENCE Overview Introduction 1 Fire-induced Ceiling-jet Flow 2 Multi-section model of Flashover 3 Fire simulation 4

3 STATE KEY LABORATORY OF FIRE SCIENCE Introduction Education Background , University of Science and Technology of China, in fire safety science, as a Ph.D. student , Lund University, as a exchange student. Research interests Confined fire dynamics (compartment, underground space, tunnel fires) Fire Simulation Project experiences Mechanism of flashover happened in regular compartment fires and tunnel fires Fire investigation and reconstruction Fire assessment and performance- based design of industrial, civil and military constructions

4 STATE KEY LABORATORY OF FIRE SCIENCE Introduction University of Science and Technology of China USTC was founded by the Chinese Academy of Sciences (CAS) in 1958 in response to the urgent need for the national economy, defense construction, and education in science and technology. It was moved to Hefei city in 1970 during the period of Cultural Revolution. Academics USTC has undertaken a large batch of national projects since its founding. 23 departments, the Special Class for the Gifted Young, three national research institutions

5 STATE KEY LABORATORY OF FIRE SCIENCE Introduction State Key Laboratory of Fire Science SKLFS was founded in 1989 in USTC. 8 research divisions: Building fire, Forest and urban fire, Industrial fire, Fire assessment, Fire chemistry, Fire detection, Fire suppression, Fire simulation It won two Follow-up Prize in the National Achievement Awards in Science and Technology, including "Early Fire Intelligent Monitoring System for Large Space Buildings " and "An Artificial Monitoring and Policy-making Support System for Preventing and Reducing the Calamities of Anhui Province"

6 STATE KEY LABORATORY OF FIRE SCIENCE Research Objective Fire Safety of tunnel and other underground corridor Until 2008, there are 1782 road tunnels (704km) and 6876 rail tunnels (3670km) in China Daegu subway fire, in South Korea in 2003, 198 killed Baku rail tunnel fire, in Azerbaijan in 1995, 300 killed Characteristics of Fire Behavior in tunnel Long and enclosed structure, fire products are confined to transfer in one or two directions Ceiling and wall insulate heat from outside Smoke and heat are difficult to exhaust Objectives Fire dynamics at pre-flashover and post-flashover period Mechanism of flashover in this long and confined space Application in fire assessment and fire reconstruction

7 STATE KEY LABORATORY OF FIRE SCIENCE Fire Development Four stages of regular fire: The growth or pre-flashover stage, flashover, the fully-developed or post-flashover stage, the decay period Flashover is a rapidly occurring transitional event in the development of a confined compartment fire

8 STATE KEY LABORATORY OF FIRE SCIENCE Tunnel Fire Experiments 5 m long reduced- scale corridor Pre-flashover and post-flashover 50 sets of tests in terms of fuel types, HRR, fire location and ventilation Measurement Temperature, Mass loss rate, gas concentration, thermal radiation flux

9 STATE KEY LABORATORY OF FIRE SCIENCE Fire plume model Conservation equations Mass, Momentum, Energy, State Fire plume Axisymmetric, Infinite linear Characteristic scale Solutions of Gaussian profile

10 STATE KEY LABORATORY OF FIRE SCIENCE Ceiling-jet Flow 3 types of ceiling-jet flow: Point source + radial flow Linear source + one-dimensional flow (confined in a corridor) Point source + one-dimensional flow (confined in a corridor) 2 types of fire influence the ceiling-jet flows: Weak fire, the plume impinges the ceiling (pre-flashover) Strong fire, the flame impinges the ceiling (post-flashover)

11 STATE KEY LABORATORY OF FIRE SCIENCE Ceiling-jet Model I Linear source + one- dimensional flow Time averaged 2D flow model in fire growth stage in terms of steady temperature, velocity and smoke thickness It is divided into 4 regions: Region (I): fire plume region Region (II): turning region during plume impingement Region (III): one-dimensional shooting flow region under the ceiling Region (IV): one-dimensional tranquil flow region under the ceiling

12 STATE KEY LABORATORY OF FIRE SCIENCE Conservation Equations Richardson Number: Wall temperature factor:

13 STATE KEY LABORATORY OF FIRE SCIENCE Scaling treatment Final ODEs: Correlation for density defect and velocity:

14 STATE KEY LABORATORY OF FIRE SCIENCE Solutions of Model I Numerical solutions of Richardson number and thickness of ceiling-jet Numerical solutions of dimensionless characteristic velocity Numerical solutions of dimensionless temperature defect

15 STATE KEY LABORATORY OF FIRE SCIENCE Ceiling-jet Model II Point source confined in a corridor Use radial model together with one- dimensional model to describe it It is divided into 6 regions Regions (I), (II) and (III) follows the previous study of radial flow, (IV) is described by a set of correlations, (V) and (VI) is calculated through one-dimensional flow model.

16 STATE KEY LABORATORY OF FIRE SCIENCE Ceiling-jet Model II Location of density jump the model (II) is valid if, where the transition from shooting flow to tranquil flow happens at a distance., a new model is required to describe the flow., a new model is required to describe the flow., the hydraulic jump moves away from the impingement point and becomes weaker. Besides, with increasing the flow will finally degenerate to an unconfined radial ceiling-jet, the hydraulic jump moves away from the impingement point and becomes weaker. Besides, with increasing the flow will finally degenerate to an unconfined radial ceiling-jet Numerical solutions of Richardson number and thickness of ceiling-jet

17 STATE KEY LABORATORY OF FIRE SCIENCE Ceiling-jet Model II Longitudinal distribution of characteristic ceiling-jet velocity Longitudinal distribution of characteristic ceiling-jet temperature and comparison with experimental results

18 STATE KEY LABORATORY OF FIRE SCIENCE Multi-section Model of Flashover Energy Equation: Mass Equation: Fire located CV Side view of a CV Division of a tunnel

19 STATE KEY LABORATORY OF FIRE SCIENCE Typical Result of simulation Temperature history during flashover Major input data 5 m corridor, 0.5×0.5m 2 Heptane, 15×15cm 2 10 Sections Result and Discussion Temperature increase sharply until it arrives at a steady value It will experiences a fluctuation period It reduce dramatically along the corridor at a given time

20 STATE KEY LABORATORY OF FIRE SCIENCE Fire simulation with SIMTEC SIMTEC (Simulation of Thermal Engineering Complex) is a large complex CFD software package developed by Dr. Zhenghua Yan in Lund University, Sweden. Including RANS and LES Unstructured mesh is valid More options for combustion, radiation models Using a separate set of solid and gas grid system

21 STATE KEY LABORATORY OF FIRE SCIENCE Pre-processing Turbulence ModelSmagorinsky Model [17] Radiation Property ModelModak’s model [18] Convective Heat TransferNon-isothermal wall function Heat Transfer Model in SolidNumerical solution using a separate set of solid grid system [19] Combustion Model A Modified Eddy Dissipation Concept (EDC) for turbulent combustion, with 4 steps global reactions C 7 H O 2 =7CO+8H Soot C 7 H1 6 +7H 2 O=7CO+15H Soot H O 2 =H 2 O CO+H 2 O=CO 2 +H 2

22 STATE KEY LABORATORY OF FIRE SCIENCE Temperature contours of modeling results

23 STATE KEY LABORATORY OF FIRE SCIENCE Comparison of temperature

24 STATE KEY LABORATORY OF FIRE SCIENCE Comparison of Gas concentration

25 STATE KEY LABORATORY OF FIRE SCIENCE Conclusion and Future Work Ceiling-jet flow model Develop a ceiling-jet flow model induced by a line fire source Propose a wall temperature factor Scaling treatment Analyze the location of density jump FW: Develop a model to describe the ceiling-jet flow induced by a strong fire, where the flame extends under the ceiling Flashover model Propose a multi-section idea, and combine with classical nonlinear theory Propose a function to simulate the transition from fuel-controlled fire to ventilation-controlled fire FW: Consider smoke layer thickness and thermal radiation effect

26 STATE KEY LABORATORY OF FIRE SCIENCE Tack så mycket 谢谢!


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