Centre de Toulouseunité MH

Thermal gradient estimation using rainbow thermometry

ONERA Research team

Nicolás GARCIA ROSAYves BISCOSGérard LAVERGNE

MUSCLES meeting Karlsruhe, September 21 2004

MUSCLES meeting -- Karlsruhe, September 21 2004

Experimental device

Temperature measurements

Objectives

Theoretical aspects

Solving methods

Thermal gradient estimations : examples

PRESENTATION OUTLINE

MUSCLES meeting -- Karlsruhe, September 21 2004

EXPERIMENTAL DEVICE

Rainbow system ;

LIF system ; Shadowgraphy

.

Monodisperse injector ; Argon laser (514,5

nm) ;

MUSCLES meeting -- Karlsruhe, September 21 2004

LIF AND RAINBOW MEASUREMENTSEvaporating 100µm droplets tinj = 54 °C ta = 24 °C

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

0 5 10 15 20 25 30 35 40 45 50 55 60

Distance to injector (mm)

Te

mp

era

ture

(°C

)

1 st order2 nd orderLIF

MUSCLES meeting -- Karlsruhe, September 21 2004

Combustion 100µm droplets tinj = 37 °C ta = 25 °C

20

25

30

35

40

45

50

55

60

65

70

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70Distance to injector (mm)

Te

mp

era

ture

(°C

)

1 st order2 nd orderLIF

LIF AND RAINBOW MEASUREMENTS

Ignitor

MUSCLES meeting -- Karlsruhe, September 21 2004

Improvement of the rainbow technique :

OBJECTIVES

considerable thermal

gradients during heating

phase

– Correction of temperature measurement ;

– Estimation of thermal gradients ;

average temperature of a heating droplet

LIF : gradient-insensitive measurement Two solving methods

MUSCLES meeting -- Karlsruhe, September 21 2004

Generalized Lorenz-Mie theory (GLMT)-based

calculations

Measurements from experimental device

evaporation model :

34.5

35

35.5

36

36.5

37

37.5

38

0 0.2 0.4 0.6 0.8 1

reduced radius r/R

Tem

per

atu

re (

in °

C)

AVAILABLE TOOLS

expected spherical temperature profile

scattered intensity

theoretical models

simple correlation

MUSCLES meeting -- Karlsruhe, September 21 2004

LIGHT SCATTERING AROUND DROPLET

correlations used

MUSCLES meeting -- Karlsruhe, September 21 2004

THEORETICAL ASPECTS

– Geometrical optics ;

– Airy-Walker theory ;

– Lorenz-Mie theory ;

– Generalized Lorenz-Mie theory.

Geometrical optics

Lorenz-Mie theory Generalized Lorenz-Mie theory

Gaussian, off-axis laser beam

MUSCLES meeting -- Karlsruhe, September 21 2004

COMBINING THE DIFFERENT TOOLS

MUSCLES meeting -- Karlsruhe, September 21 2004

SOLUTION OF THE SYSTEM

MUSCLES meeting -- Karlsruhe, September 21 2004

RECALL OF THE TWO SOLVING METHODS

MUSCLES meeting -- Karlsruhe, September 21 2004

SIMULTANEOUS MEASUREMENT of MEAN TEMPERATURE and THERMAL

GRADIENT

2-periodicity :multiple

solutions !

MUSCLES meeting -- Karlsruhe, September 21 2004

GRADIENT ESTIMATIONS : evaporating droplets

set-up

Airy-Walker classical rainbow inversion

Airy-Walker classical rainbow inversion

LIF measurement

Rainbow/LIF estimation

MUSCLES meeting -- Karlsruhe, September 21 2004

GRADIENT ESTIMATIONS : burning droplets

set-up

Airy-Walker classical rainbow inversion

Airy-Walker classical rainbow inversion

LIF measurement

Rainbow/LIF estimation

MUSCLES meeting -- Karlsruhe, September 21 2004

CONCLUSIONS, PERSPECTIVES

–New correlation obtained from the fringe pattern phase in forward direction.

–The coupling LIF / Rainbow gives a good evaluation of the thermal gradients, especially in burning regime.

–The second order rainbow provided no additional information.

–Some problems must be resolved to get simultaneously the mean temperature and the thermal gradients from the above refractometry technique.

–Actually the coupling of the two techniques : Infrared and Rainbow is going on. The obtention of the surface temperature by infrared method will be another important information to be used for the validation of thermal gradients measurement.

MUSCLES meeting -- Karlsruhe, September 21 2004

1

2,

).(5

2

kThccn e

hcTL

IR MEASUREMENT

IR thermal flux

IR detector

T°cn

Black body spectral energy Planck ‘s law

with : h = Planck’s constant = 6.6262 10-34 J.K-1

k = Boltzmann’s constant = 1.3806 10 -23 J.K-1

c = Light speed = 2.9979 108 m.s-1

Thermal flux emission in the IR range

en [W.Sr-1.m-3]

Black body

...)(.,, gcng TLTL Real body brightness

MUSCLES meeting -- Karlsruhe, September 21 2004

MESUREMENT TECHNIQUE : SIGNAL SHUT-OFF METHOD

Black body

Droplet stream

injector

IR signal

Peri

od

T

IR detector

+ non-intrusive+ no calibration needed+ correction of the system’s non-linearities- droplet position / time relation

Time

Voltage

V=0 => equal fluxes

Droplet signal ( Tgoutte > Tcn )

Blackbody signal

Period T

MUSCLES meeting -- Karlsruhe, September 21 2004

SPECTRAL BAND SELECTION :MEASUREMENT PROCESS

),(

1.

sin. 02 TAd

fDTEB

[K]

with

dTLT

DT goutteBLIPgoutte .,).().(),( *

: merit factor

1E+8

1E+9

1E+10

270 280 290 300 310 320 330

Droplets temperature (K)

Band 3-5 micronsBand 8-12 microns

DTEBEmissivity

Emissivity calculated by Mie theory

Ethanol droplets

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Wavelength (µm)

Em

issi

vity

Droplet emissivity

Detector 10.13 spectral reponse

Droplet

AmbientField of view

Lens aperture

Sensor (Ad)

Cold filterLens