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