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
Overview
1
Introduction
2
Fire-induced Ceiling-jet Flow
3
Multi-section model of Flashover
4
Fire simulation
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Introduction
Education Background
2006-2011, 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 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 performancebased 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.
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
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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 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
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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 reducedscale 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 equations
Mass, 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 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)
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Ceiling-jet Model I
Linear source + onedimensional 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
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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
Numerical
solutions
solutions
of of
dimensionless
Richardson
Numerical solutions of dimensionless
number
characteristic
and thickness
velocity
of ceiling-jet
temperature defect
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Ceiling-jet Model II
Point source confined in a corridor
Use radial model together with onedimensional 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.
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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.
, 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
temperature
and
with
Longitudinal
distribution
of comparison
characteristic
experimental
results
ceiling-jet velocity
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Multi-section Model of Flashover
Division of a tunnel
Energy Equation:
Side view of a CV
Mass Equation:
Fire located CV
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Typical Result of simulation
Major input data
5 m corridor, 0.5×0.5m2
Heptane, 15×15cm2
10 Sections
Result and Discussion
Temperature history during flashover
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 LES
Unstructured mesh is valid
More options for combustion, radiation models
Using a separate set of solid and gas grid system
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Pre-processing
Turbulence Model
Radiation Property Model
Convective Heat Transfer
Heat Transfer Model in Solid
Smagorinsky Model [17]
Modak’s model [18]
Non-isothermal wall function
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+0.05Soot
C7H16+7H2O=7CO+15H2+0.05Soot
H2+0.5O2=H2O
CO+H2O=CO2+H2
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Temperature contours of modeling results
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Comparison of temperature
b
TC 4 from experiment
TC 4 from SIMTEC (coarse grid)
TC 4 from SIMTEC (fine grid)
1400
1200
1200
1000
1000
800
600
400
TC 7 from experiment
TC 7 from SIMTEC (coarse grid)
TC 7 from SIMTEC (fine grid)
1400
Temperature(℃)
Temperature(℃)
a
200
800
600
400
200
0
0
100
200
300
0
400
0
Time (s)
1400
d
1200
1000
1000
800
600
400
200
300
400
Time (s)
TC 13 from experiment
TC 13 from SIMTEC (coarse grid)
TC 13 from SIMTEC (fine grid)
1400
1200
Temperature(℃)
Temperature(℃)
c
TC 10 from experiment
TC 10 from SIMTEC (coarse grid)
TC 10 from SIMTEC (fine grid)
100
800
600
400
200
200
0
0
0
100
200
Time (s)
300
400
0
100
200
Time (s)
300
400
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Comparison of Gas concentration
a
16
14
14
12
12
10
10
8
6
8
6
4
4
2
2
0
0
100
200
300
Probe 7 from Test 1.b
Probe 7 from SIMTEC (fine grid)
16
CO2()
CO2()
b
Probe 4 from Test 1.a
Probe 4 from SIMTEC (fine grid)
0
400
0
100
Time(s)
a
300
400
Time(s)
Probe 4 from Test 1.a
Probe 4 from SIMTEC (fine grid)
20000
200
Probe 7 from Test 1.b
Probe 7 from SIMTEC (fine grid)
b
14000
17500
12000
15000
CO (ppm)
CO (ppm)
10000
12500
10000
7500
8000
6000
5000
4000
2500
2000
0
0
0
100
200
Time (s)
300
400
0
100
200
300
400
Time (s)
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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
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Tack så mycket
谢谢！
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