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LES of Vertical Turbulent Wall Fires
Ning Ren1, Yi Wang1, Sebastien Vilfayeau2, Arnaud Trouvé2
1. FM Global, Research, Norwood, MA, USA2. University of Maryland, College Park, MD, USA
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Background Industrial-scale fire tests
– Reduce fire loses– Expensive– Limited configurations
Fire modeling– Understand physics– Reduce large scale tests
Challenges– Multi-physics– Multi-phases
Slide 2
6 m
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Slide 3
Background
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Tools – FireFOAM Open-source fire model (FM Global)
– www.fmglobal.com/modeling (2008-Present) Based on OpenFOAM
– A general-purpose CFD toolbox (OpenCFD, UK)
Main features– Object-oriented C++ environment– Advanced meshing capabilities– Massively parallel capability (MPI-based)– Advanced physical models:
• turbulent combustion, radiation• pyrolysis, two phase flow, suppression, etc.
Slide 4
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Slide 5
Background
• Multi-physics interaction• Difficult to instrument
• Vertical wall fire is a canonical problem
• Industrial-scale Fire Test
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Background Experiments
– Orloff, L., et.al (1974) PMMA– Ahmad, T., et.al (1979) – Markstein, G.H., de Ris, J. (1990)– de Ris, J., et.al (1999)
Modeling– Tamanini, F. (RANS,1975) PMMA– Kennedy, L.A., et.al (RANS,1976)– Wang, Y.H., et.al (RANS, 1996)– Wang, Y.H., et.al (FDS, 2002)– Xin, Y. (FDS, 2008)
Slide 6
Orloff, L, et.al (PMMA)
Challenges– High grid requirement– Buoyancy driven– Mass transfer– Reacting boundary flow
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Experiments – Prescribed flow rates
– Propylene– Methane– Ethane– Ethylene
Water cooled vertical wall Diagnostics
– Temperature– Radiance– Heat flux– Soot depth
Slide 7
(J. de Ris et al., FM, 1999)(J. de Ris et al., Proc. 7th IAFSS, 2002)
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Grid requirement Momentum driven flow (Piomelli et
al., 2002)
Natural convection (Holling et al., 2005)
Wall Fires– 10~20 cells across the flame
• 3mm to start
Slide 8
2 cm
mmww
wVSL 2.0
)/( 2/1
mmgcq wpwcw
wVSL 5.0
)()/(Pr)/(
4/14/1,,
4/3
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Mesh and B.C. Base line – 3 mm grid
– ΔY ~ 3 mm, ΔX ~ 7.5 mm, ΔZ ~ 7.7 mm (ΔX :ΔY :ΔZ ~ 2.5:1:2.5)
– 0.8 M cells, CFL = 0.5– 1.5, 2, 3, 5, 10, 15 and 20 mm
B.C.– Cyclic (periodic) in span-wise – Entrainment BC at the side– Fixed temperature, T = 75 ˚C– Propylene
• 8.8, 12.7, 17.1, 22.4 g/m2s
Slide 9
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Turbulence Model
Slide 10
4/52/5
2/32
dij
dijijij
dij
dij
wsgsSSSS
SSC
2/1sgsksgs kC
i
j
j
iij
i
j
j
iij
mnmnmnmnijkjikkjikdij
xu
xu
xu
xuS
SSSSS
~~
21~ ,
~~
21~
~~~~31~~~~
sgsijijsgsi
i
k
ksgssgs
i
sgssgs
ii
isgssgs
SSxu
xuk
xk
xxuk
dtkd
~~2~~
32
~Zero for pure shear flow
O(y3) near wall scaling
Two deficiencies:1. Laminar region with pure shear2. Wrong scaling at near wall
region O(1) instead of O(y3)
K-equation model WALE Model
/2/3sgsesgs kC
No need to calculate ksgs
Wall adaptive local eddy viscosity model
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Wall-Adaptive Local Eddy Viscosity
Slide 11
K-Eqn Model WALE Model
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0 0.02 0.04 0.06 0.08 0.1 0.12
μ sgs
/μai
r,∞
Y [m]
k-equation
WALE
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis Modelk-equationWALE
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Combustion Model Eddy Dissipation Concept (EDC model)
– Mixing controlled reaction
Slide 12
)~
,~min( 2
s
OF
tEDCF r
YYC
2/1~~sgssgs
sgst k
k
K-equation model WALE model
2/3
4/52/52 ~~
~~dij
dij
dij
dijijij
sgst
SS
SSSS
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Slide 13
Combustion Model Eddy Dissipation Concept (EDC model)
– Mixing controlled reaction
)~
,~min(/ ,/min
2
s
OF
ddEDCtF r
YY
CC
sgst
2
~
2
~ d
EDCt
dd
CCR
//
Turbulence reaction rate
Diffusion reaction rate
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Radiation Model Fixed radiant fraction Finite volume implementation of Discrete
Ordinate Method (fvDOM) Optically thin assumption
Soot/gas blockage (χrad is reduced by 25%)
Slide 14
)4
(
crad qdsdI
Fuel Methane
CH4
EthaneC2H6
Ethylene C2H4
Propylene C3H6
Wall Fire(de Ris measurement) 15% 17% 24% 32%
Simulation (account for blockage) 12% 13% 18% 25%
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Slide 15
Flame topologyK K
m/s m/s m/s m/s
span-wise wall-normal stream-wise
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Slide 16
Flame topology
ijijijij SSQ ~~~~21
Wallace, J.M., 1985
kg/m/s kg/m/s
Q, wall-normal view
i
j
j
iij
i
j
j
iij x
uxu
xu
xuS
~~
21~ ,
~~
21~
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Slide 17
Heat flux – (de Ris Model)
sradfvTTCkfwradfswr eTTq ,111 44
,''
1
/0
" /
0"
''hCm
pf
A
RActc
pfe
hCms
Hhq
Blockage Side-wall Flame radiationtemperature
Flame emissivity
Soot volumefraction
Soot depth
Heat transfercoefficient Fuel blowing effect
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Slide 18
Grid Convergence ( =17.1 g/m2s, C3H6) m
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Rad
iativ
e H
eat F
lux
[kW
/m2 ]
Z [m]
1.5 mm2 mm3 mm5 mm10 mm15 mm20 mmdeRis Model
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis Model1.5 mm2 mm3 mm5 mm10 mm15 mm20 mm
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Tota
l Hea
t Flu
x [k
W/m
2 ]
Z [m]
1.5 mm 2 mm3 mm 5 mm10 mm 15 mm20 mm deRis ModelExperiment
Fully Turbulent
Fully Turbulent
Fully Turbulent
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Slide 19
Heat Flux – Flow Rates (Δ=3 mm, C3H6)
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Rad
iativ
e H
eat F
lux
[kW
/m2 ]
Z [m]
deRis, 8.8deRis, 12.7deRis, 17.1deRis, 22.4fireFoam, 8.8fireFoam, 12.7fireFoam, 17.1fireFoam, 22.4
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis, 8.8deRis, 12.7deRis, 17.1deRis, 22.4fireFoam, 8.8fireFoam, 12.7fireFoam, 17.1fireFoam, 22.4
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Tota
l Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis, 8.8deRis, 12.7deRis, 17.1deRis, 22.4fireFoam, 8.8fireFoam, 12.7fireFoam, 17.1fireFoam, 22.4
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Slide 20
Heat Flux – Fuels (Δ=3 mm)
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Tota
l Hea
t Flu
x [k
W/m
2 ]
Z [m]
fireFoam, CH4, 10.6 fireFoam, C2H4, 11.5fireFoam, C2H6, 10.2 fireFoam, C3H6, 17.1Exp, CH4, 10.6 Exp, C2H4, 11.5Exp, C2H6, 10.2 Exp, C3H6, 17.1
0
5
10
15
20
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Rad
iativ
e H
eat F
lux
[kW
/m2 ]
Z [m]
deRis, CH4, 10.6deRis, C2H4, 11.5deRis, C2H6, 10.2deRis, C3H6, 17.1fireFoam, CH4, 10.6fireFoam, C2H4, 11.5fireFoam, C2H6, 10.2fireFoam, C3H6, 17.1
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis, CH4, 10.6deRis, C2H4, 11.5deRis, C2H6, 10.2deRis, C3H6, 17.1fireFoam, CH4, 10.6fireFoam, C2H4, 11.5fireFoam, C2H6, 10.2fireFoam, C3H6, 17.1
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Slide 21
Convective Heat Flux: Blowing Effect
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis, 8.8deRis, 17.1deRis, 29.3fireFoam, 8.8fireFoam, 17.1fireFoam, 29.3
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis modelfireFoam, 1 mmfireFoam, 1.5 mmfireFoam, 3 mmfireFoam, 6 mmfireFoam, 9 mmfireFoam, 12 mmfireFoam, 15 mm
PyrolysisZone
FlamingZone
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis, 8.8deRis, 17.1deRis, 29.3fireFoam, 8.8fireFoam, 17.1fireFoam, 29.3
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis modelfireFoam, 1 mmfireFoam, 1.5 mmfireFoam, 3 mmfireFoam, 6 mmfireFoam, 9 mmfireFoam, 12 mmfireFoam, 15 mm
PyrolysisZone
FlamingZone
17.1g/m2s
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Slide 22
Temperature (C3H6)
300
600
900
1200
1500
0 0.5 1 1.5 2 2.5 3
T [K
]
Y/δsoot
400
700
1000
1300
0 0.5 1 1.5 2 2.5 3
T [K
]
Y/YT=1000K
Z=0.57Z=0.67Z=0.77Z=0.87Z=0.97
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Summary and future work Summary
– Near wall turbulence and combustion models are important– Good agreements are obtained for wall-resolved modeling– 10~20 cells across the flame are needed– Convective heat flux is important in the downstream flaming zone
Future work– Test soot model for radiation– Improve turbulence and combustion models for coarse-grained
modeling– Wall function study
Slide 23
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Cyu ln1
yu
uuu
yuy
wu
Ongoing work – wall function Log-Law
Blowing effect (Stevenson, 1963)
Slide 24
5.5ln41.01
yu
5.5ln41.01112 2/1
yuV
V bb
w
ww
wwsgs
yu
,
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Slide 25
Ongoing work – wall function
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
wall-resolved, 1 mmno wall function, 15 mmlog-law, 15 mmStevenson, 15 mm
(Δ=15 mm)
(17.1 g/m2s, C3H6)
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Slide 26
Ongoing work – wall function
1
////
0"
''
0"
pf Chm
pf
A
RActc
e
Chms
Hhq
Fuel blowing effect
5.5ln41.01
yu
wChm
pf
ww
wwsgs
pfe
Chm
yu
1
////
0"
,0
"
0
5
10
15
20
25
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
8.8, wall-resolved8.8, wall function17.1, wall-resolved17.1, wall function29.3, wall-resolved29.3, wall function
(Δ=15 mm)
J/g/K 8.1/K W/m16 2
0
pCh
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Acknowledgement John de Ris
Funded by FM Global– Strategic research program on fire modeling
Slide 27
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Slide 28
Temperature (C3H6)
300
600
900
1200
1500
0 0.5 1 1.5 2 2.5 3
T [K
]
Y/δsoot
400
700
1000
1300
0 0.5 1 1.5 2 2.5 3
T [K
]
Y/YT=1000K
Z=0.57Z=0.67Z=0.77Z=0.87Z=0.97
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Slide 29
Temperature – Elevation (17.1 g/m2s, C3H6)
300
600
900
1200
0 0.02 0.04 0.06 0.08 0.1 0.12
T [K
]
Y [m]
Z=0.57Z=0.67Z=0.77Z=0.87Z=0.97
300
600
900
1200
0 0.5 1 1.5 2 2.5 3
T [K
]
Y*
Z=0.57Z=0.67Z=0.77Z=0.87Z=0.97
Inner layerOuter layer
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Coarse grid Convective heat flux
– Temperature gradient– Combustion
Slide 30
300
600
900
1200
1500
0 0.02 0.04 0.06 0.08 0.1 0.12
T [K
]
Y [m]
1.5 mm2 mm3 mm5 mm10 mm15 mm20 mm
0
1
2
3
4
5
0 0.02 0.04 0.06 0.08 0.1 0.12
Uz
[m/s
]
Y [m]
1.5 mm2 mm3 mm5 mm10 mm15 mm20 mm
Radiative heat flux– Combustion
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Slide 31
A temporary approach
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t Flu
x [k
W/m
2 ]
Z [m]
deRis Model
k-equation
k-equation WALE
WALE
300
600
900
1200
1500
0 0.02 0.04 0.06 0.08 0.1
T [K
]
Y [m]
WALE, 1.5 mm
WALE, 15 mm
WALE-oneEqEddy, 15 mm
4/52/5
2/32
dij
dijijij
dij
dij
wsgsSSSS
SSC
2/1
sgsksgs kC
sgsijijsgsi
i
k
ksgssgs
i
sgssgs
ii
isgssgs
SSxu
xuk
xk
xxuk
dtkd
~~2~~
32
~
2/1~~sgssgs
sgst k
k
K-equation K-equation, WALE
Minimize the influence of combustionBetter turbulence & combustion model needed in future
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32
300
600
900
1200
1500
0 0.02 0.04 0.06 0.08 0.1 0.12
Tc [K
]
Y [m]
deRis, 8.8deRis, 12.7deRis, 17.1deRis, 22.4fireFoam, 8.8fireFoam, 12.7fireFoam, 17.1fireFoam, 22.4
0
1
2
3
4
5
0 0.02 0.04 0.06 0.08 0.1 0.12
Uz
[m/s
]
Y [m]
fireFoam, 8.8
fireFoam, 12.7
fireFoam, 17.1
fireFoam, 22.4