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

STATE KEY LABORATORY OF FIRE SCIENCE

Overview

Introduction1

Fire-induced Ceiling-jet Flow2

Multi-section model of Flashover3

Fire simulation4

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Introduction

Education Background2006-2011, University of Science and

Technology of China, in fire safety science, as a Ph.D. student.

2010-2011, Lund University, as a exchange student.

Research interestsConfined fire dynamics (compartment,

underground space, tunnel fires)Fire Simulation

Project experiencesMechanism of flashover happened in

regular compartment fires and tunnel fires

Fire investigation and reconstructionFire assessment and performance-

based design of industrial, civil and military constructions

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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.

AcademicsUSTC has undertaken a large batch of

national projects since its founding.23 departments, the Special Class for

the Gifted Young, three national research institutions

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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"

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Research Objective

Fire Safety of tunnel and other underground corridor Until 2008, there are 1782 road tunnels (704km) and 6876 rail

tunnels (3670km) in ChinaDaegu subway fire, in South Korea in 2003, 198 killedBaku rail tunnel fire, in Azerbaijan in 1995, 300 killed

Characteristics of Fire Behavior in tunnelLong and enclosed structure, fire products are confined to transfer in

one or two directionsCeiling and wall insulate heat from outsideSmoke and heat are difficult to exhaust

ObjectivesFire dynamics at pre-flashover and post-flashover periodMechanism of flashover in this long and confined spaceApplication in fire assessment and fire reconstruction

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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

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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

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Fire plume model

Conservation equationsMass, Momentum, Energy, State

Fire plume Axisymmetric, Infinite linear

Characteristic scale

Solutions of Gaussian profile

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Ceiling-jet Flow

3 types of ceiling-jet flow:Point source + radial flowLinear 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)

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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 regionRegion (II): turning region during

plume impingementRegion (III): one-dimensional

shooting flow region under the ceiling

Region (IV): one-dimensional tranquil flow region under the ceiling

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Conservation Equations

Richardson Number: Wall temperature factor:

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Scaling treatment

Final ODEs: Correlation for density defect and velocity:

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Solutions of Model I

Numerical solutions of Richardson number and thickness of ceiling-jet

Numerical solutions of dimensionless characteristic velocityNumerical solutions of dimensionless

temperature defect

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Ceiling-jet Model II

Point source confined in a corridorUse radial model together with one-dimensional model to describe itIt is divided into 6 regionsRegions (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.

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Ceiling-jet Model II

Location of density jumpthe 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. , 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

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Ceiling-jet Model II

Longitudinal distribution of characteristic ceiling-jet velocity

Longitudinal distribution of characteristic ceiling-jet temperature and comparison with

experimental results

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Multi-section Model of Flashover

Energy Equation: Mass Equation:

Fire located CV

Side view of a CVDivision of a tunnel

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Typical Result of simulation

Temperature history during flashover

Major input data5 m corridor, 0.5×0.5m2 Heptane, 15×15cm2

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

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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 LESUnstructured mesh is validMore options for combustion, radiation modelsUsing a separate set of solid and gas grid system

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Pre-processing

Turbulence Model Smagorinsky Model [17]Radiation Property Model Modak’s model [18]Convective Heat Transfer Non-isothermal wall functionHeat Transfer Model in Solid Numerical 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

C7H16+3.5O2=7CO+8H2+0.05SootC7H16+7H2O=7CO+15H2+0.05SootH2+0.5O2=H2OCO+H2O=CO2+H2

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Temperature contours of modeling results

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Comparison of temperature

0 100 200 300 4000

200

400

600

800

1000

1200

1400

Tem

pera

ture

(℃)

Time (s)

TC 4 from experiment TC 4 from SIMTEC (coarse grid) TC 4 from SIMTEC (fine grid)

a

0 100 200 300 4000

200

400

600

800

1000

1200

1400

Tem

pera

ture

(℃)

Time (s)

TC 7 from experiment TC 7 from SIMTEC (coarse grid) TC 7 from SIMTEC (fine grid)

b

0 100 200 300 4000

200

400

600

800

1000

1200

1400 TC 10 from experiment TC 10 from SIMTEC (coarse grid) TC 10 from SIMTEC (fine grid)

Tem

pera

ture

(℃)

Time (s)

c

0 100 200 300 4000

200

400

600

800

1000

1200

1400

TC 13 from experiment TC 13 from SIMTEC (coarse grid) TC 13 from SIMTEC (fine grid)

Tem

pera

ture

(℃)

Time (s)

d

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Comparison of Gas concentration

0 100 200 300 4000

2

4

6

8

10

12

14

16 Probe 4 from Test 1.a Probe 4 from SIMTEC (fine grid)

CO

2()

Time(s)

a

0 100 200 300 4000

2

4

6

8

10

12

14

16 Probe 7 from Test 1.b Probe 7 from SIMTEC (fine grid)

CO

2()

Time(s)

bCO2

0 100 200 300 4000

2500

5000

7500

10000

12500

15000

17500

20000

CO

(pp

m)

Time (s)

Probe 4 from Test 1.a Probe 4 from SIMTEC (fine grid)a

0 100 200 300 4000

2000

4000

6000

8000

10000

12000

14000

Probe 7 from Test 1.b Probe 7 from SIMTEC (fine grid)

CO

(pp

m)

Time (s)

bCO

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Conclusion and Future Work

Ceiling-jet flow model Develop a ceiling-jet flow model induced by a line fire sourcePropose a wall temperature factorScaling treatmentAnalyze 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

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Tack så mycket谢谢！