osu analysis with fds - home : faa fire safety

OSU Analysis with FDS

Haiqing Guo, Mike Burns, Richard E. Lyon

William J. Hughes Technical Center, FAA, Atlantic City, NJ

Introduction

2

• OSU test instrument is subject certain level of irreproducibility.

• There exists certain time delay on the OSU signal response.

• More accurate and more reliable HRR test method needs better understanding of the current OSU design.

• Perform detailed characterization and heat transfer analysis (analytical and numerical) on OSU.

Representative OSU Tests

3

-10

0

10

20

30

40

50

60

0 50 100 150 200 250 300

Hea

t R

ele

ase

Ra

te (

kW

/m2)

Time (s)

Split Ratio, 1:2.2

Split Ratio, 1:3.0

Split Ratio, 1:4.3

Blank, 1:3.0

-20

-10

0

10

20

30

40

50

60

0 50 100 150 200 250 300Hea

t R

elea

se R

ate

(kW

/m2)

Time (s)

A24

0

10

20

30

40

50

60

0 50 100 150 200 250 300

Hea

t R

elea

se R

ate

(kW

/m2)

Time (s)

B09

Schneller Panel Test

smeared HRR

unreal HRR

different blank run

OSU Calibration

4

air temp

cone temp

hot gas temp

TP temp

hot gas hot gas air

300

400

500

600

700

800

0 500 1000 1500 2000 2500

Tem

pera

ture

(K

)

Time (s)

Split Ratio, 1:2

300

400

500

600

700

800

0 500 1000 1500 2000 2500

Tem

pera

ture

(K

)

Time (s)

Split Ratio, 1:3

300

400

500

600

700

800

0 500 1000 1500 2000 2500

Tem

pera

ture

(K

)

Time (s)

Split Ratio, 1:4

hot gas

thermopile

inner cone

plenum air

hot gas

thermopile

inner cone

plenum air

hot gas

thermopile

inner cone

plenum air

standard calibration procedure + detailed characterization

Thermal Analysis on Inner Cone

5

T1 T2

Tw

outer cone

inner cone

dt

dTcATTAhTTAh w

ww 2211

c

hht

ww ehh

ThThT

hh

ThThT

21

21

22110,

21

2211

Split Ratio (1:2) Split Ratio (1:3) Split Ratio (1:4)

h1 (W/m2-K) 5.5 6.0 6.5

h2 (W/m2-K) 27.2 41.2 49.1

τ (s) 60 42 35

energy equation:

1-D Model

square wave constant

time constant

6

350

400

450

500

0 500 1000 1500

Th

erm

opile

Te

mp

era

ture

(K

)

Time (s)

Split Ratio 2:1

Split Ratio 3:1

Split Ratio 4:1

Cone Wall Effects on Thermopile

Based on inner cone wall temperature, plenum air and hot gas temperature, the thermopile temperature can be calculated using mixing theory.

CFD Modeling (2D Model)

7

hot gasair

400

420

440

460

480

350

400

450

500

550

600

2900 3000 3100 3200 3300

Th

erm

opile

Te

mp. (K

)

Co

ne

Wa

ll T

em

p. (K

)

Time (s)

Thermopile

T5

T3

T1

• 2-D FDS model. • Hot gas T is following a step change. • Air T is constant. • Both Ts are based on the characterization results.

Model of Sample / Holder Insertion

8

heater

air

air

plate

air

air

heater

(1) (2)

x0

10

20

30

40

0

1

1800 1900 2000 2100 2200 2300 2400 2500

Fire

HR

R (

kW/m

2)

Sam

ple

Sta

tus

(-)

Time (s)

sample insertion

Sample Holder Effect

9

-20

-10

0

10

20

30

40

450

500

550

600

1500 1700 1900 2100 2300 2500

Pre

scri

bed

HR

R (

kW/m

2)

Ther

mo

pile

Tem

per

atu

re (

°C)

Time (s)

Dummy sample

Dummy sample+Fire

Prescribed HRR

0

5

10

15

20

25

30

35

0

10

20

30

40

50

60

70

1500 1700 1900 2100 2300 2500

Pre

scri

be

d H

RR

(kW

/m2)

Tem

per

atu

re D

iffe

ren

ce (

°C)

Time (s)

Temp. Difference

Prescribed HRR

The modeled thermopile temperature is overlaid with prescribed HRR for comparison.

Thermopile temperature after baseline subtraction.

holder insertion

Sample Holder Effect on Heat Flux

10

heater

air

air

plate

air

air

heater

(1) (2)

x

Sample holder increases surface area for heat convection and hence increase the thermopile temperature.

holder insertion holder insertion

Summary

• Upper region, the double-cone system dominates the dynamics of the system.

• Lower region, the sample holder causes unreal heat release signal. Blank run with a dummy sample needs to be subtracted.

• etc.

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