les of vertical turbulent wall fires ning ren 1, yi wang 1, sebastien vilfayeau 2, arnaud trouvé 2...
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LES of Vertical Turbulent Wall Fires
Ning Ren1, Yi Wang1, Sebastien Vilfayeau2, Arnaud Trouvé2
1. FM Global, Research, Norwood, MA, USA
2. University of Maryland, College Park, MD, USA
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
Slide 3
Background
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
Slide 5
Background
• Multi-physics interaction• Difficult to instrument
• Vertical wall fire is a canonical problem
• Industrial-scale Fire Test
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
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)
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
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
Turbulence Model
Slide 10
4/52/5
2/3
2
dij
dijijij
dij
dij
wsgsSSSS
SSC
2/1sgsksgs kC
i
j
j
iij
i
j
j
iij
mnmnmnmnijkjikkjikdij
x
u
x
u
x
u
x
uS
SSSSS
~~
2
1~ ,
~~
2
1~
~~~~
3
1~~~~
sgsijijsgsi
i
k
ksgssgs
i
sgssgs
ii
isgssgs
SSx
u
x
uk
x
k
xx
uk
dt
kd
~~2
~~
3
2
~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
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
μsg
s/μ
air,
∞
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 F
lux
[kW
/m2]
Z [m]
deRis Model
k-equation
WALE
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
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
C
CR
/
/
Turbulence reaction rate
Diffusion reaction rate
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 q
ds
dI
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%
Slide 15
Flame topology
K K
m/s m/s m/s m/s
span-wise wall-normal stream-wise
Slide 16
Flame topology
ijijijij SSQ~~~~
2
1
Wallace, J.M., 1985
kg/m/s kg/m/s
Q, wall-normal view
i
j
j
iij
i
j
j
iij x
u
x
u
x
u
x
uS
~~
2
1~ ,
~~
2
1~
Slide 17
Heat flux – (de Ris Model)
sradfvTTCkfwradfswr eTTq ,111 44
,''
1
/0
" /
0"
''
hCm
pf
A
RActc
pfe
hCm
sHhq
Blockage Side-wall Flame radiationtemperature
Flame emissivity
Soot volumefraction
Soot depth
Heat transfercoefficient Fuel blowing effect
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
Flu
x [k
W/m
2]
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 F
lux
[kW
/m2]
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 F
lux
[kW
/m2]
Z [m]
1.5 mm 2 mm3 mm 5 mm10 mm 15 mm20 mm deRis ModelExperiment
Fully Turbulent
Fully Turbulent
Fully Turbulent
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
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
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t 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
25
30
35
40
0 0.2 0.4 0.6 0.8 1
Tota
l Hea
t F
lux
[kW
/m2]
Z [m]
deRis, 8.8deRis, 12.7deRis, 17.1deRis, 22.4fireFoam, 8.8fireFoam, 12.7fireFoam, 17.1fireFoam, 22.4
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 F
lux
[kW
/m2]
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
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
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Con
vect
ive
Hea
t 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
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 F
lux
[kW
/m2]
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 F
lux
[kW
/m2]
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 F
lux
[kW
/m2]
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 F
lux
[kW
/m2]
Z [m]
deRis modelfireFoam, 1 mmfireFoam, 1.5 mmfireFoam, 3 mmfireFoam, 6 mmfireFoam, 9 mmfireFoam, 12 mmfireFoam, 15 mm
PyrolysisZone
FlamingZone
17.1g/m2s
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
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
Cyu ln1
yu
u
uu
yu
y
wu
Ongoing work – wall function
Log-Law
Blowing effect (Stevenson, 1963)
Slide 24
5.5ln41.0
1 yu
5.5ln41.0
111
2 2/1
yuVV
b
b
w
w
w
wwsgs
y
u
,
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 F
lux
[kW
/m2]
Z [m]
wall-resolved, 1 mmno wall function, 15 mmlog-law, 15 mmStevenson, 15 mm
(Δ=15 mm)
(17.1 g/m2s, C3H6)
Slide 26
Ongoing work – wall function
1
////
0"
''
0"
pf Chm
pf
A
RActc
e
Chm
sHhq
Fuel blowing effect
5.5ln41.0
1 yu
wChm
pf
w
w
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 F
lux
[kW
/m2]
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 20
pC
h
Acknowledgement
John de Ris
Funded by FM Global– Strategic research program on fire modeling
Slide 27
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
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=0.57
Z=0.67
Z=0.77
Z=0.87
Z=0.97
300
600
900
1200
0 0.5 1 1.5 2 2.5 3
T [K
]
Y*
Z=0.57
Z=0.67
Z=0.77
Z=0.87
Z=0.97
Inner layerOuter layer
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
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 F
lux
[kW
/m2]
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
2/3
2
dij
dijijij
dij
dij
wsgsSSSS
SSC
2/1
sgsksgs kC
sgsijijsgsi
i
k
ksgssgs
i
sgssgs
ii
isgssgs
SSx
u
x
uk
x
k
xx
uk
dt
kd
~~2
~~
3
2
~
2/1~~sgssgs
sgst
k
k
K-equation K-equation, WALE
Minimize the influence of combustionBetter turbulence & combustion model needed in future
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
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