Arvind Rao & J.P. Buijtenen

Infrared Signature Modeling of Infrared Signature Modeling of Aircraft Exhaust PlumeAircraft Exhaust Plume

Faculty of Aerospace Engineering

Aircraft Survivability

It has been observed that linear changes in aircraft survivability produce exponential changes in force effectiveness and aircraft attrition rates. Thus, stealth technology helps aircraft to avoid high aircraft loss rates and completet h e m i s s i o n o b j e c t i v e s e f f e c t i v e l y

Leading Edge

Aircraft Nose

Inlet Lip Drop Tank Nose

FuselageNozzle

Exhaust Plume

Sun Glint

Sources of Infrared Signatures

Radar

Exhaust plume, exhaust duct, tail boom heated by exhaust plume and the direct view of hot engine parts like turbine blades. Engine parts at a temperature of 600-700oC.

Infrared Signatures Sources in a Helicopter

Tail boom heated by plume

Engine & Exhaust

AIM 4D, AIM 9L/M (Sidewinder), ASRAAM, MICA, Mistral, Python-3, R.530,

R.550, Shafrir, Stinger

AA-2, AA-3, AA-5, AA-6, AA-8, AA-10, AA-11, PL-2, PL-

5B, PL-7

Air to Air (AAM)

Chaparral, Mistral, Redeye, Stinger SA-7, SA-9, SA-13, SA-14, SA-16, SA-18

Surface to Air (SAM)

Western MissilesSoviet Block MissileMissile Type

Common heat-seeking missiles and their origin

The IR Threat

Plume IR Signature Modelling

5km

0º (Horizon)180ºSAM

90º (Zenith)

A Simple Mission

M = 0.8

The Modeling Strategy

ωd

∑ωplDetector element

Reticle

MISSILE IR SEEKER

IR Transparentwindow R

SAM

Plume (discretised)

aircraft

SAM IR Seeker (instantaneous field of view )

[ ] ( ) ( )( )min

1,

1,,,,,, )1(

ξ⋅

τ⋅⎭⎬⎫

⎩⎨⎧

−+−+τ−−∑ ∑= =

NEI

AIIAIIAII atm

N

itptpbgtp

N

ifuseifusebgfuseipliplplbgpli

pl fuse

RLO =

CFD Simulation of the Exhaust Plume

Nozzle exit plane

Diamond ShockExpansion fans

Mac

h N

o.

Magnified view

Direction of the Plume

Plume center line

Plume Mach number contours obtained from CFD

Nozzle exit plane

Diamond Shock

Stat

ic T

empe

ratu

re (K

)

Magnified view

Direction of the Plume

Plume center line

Plume static temperature contours obtained from CFD

Validation of the Exhaust Plume Simulation

Y/Rnz

0

0 .1

0 .2

0 .3

0 .4

0 .5

0 .6

0 .7

0 .8

0 .9

1

0 0.5 1 1.5 2 2.5 3 3.5 4

"te mp .txt ""te mp .txt "

"te mp _h.tx t "

(T-T

amb)/

(Tc-T

amb)

PresentGauffre

Heragu etal

Temperature profile across the jet at X/DN =10

Y/Rnz

Concentration profile across the jet at X/DN =10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3 3.5

"CO2.txt""CO2.txt""CO2.txt"

C/C

C

PresentGauffre

Heragu etal

0

50

100

150

200

250

300

350

400

450

500

3 4 5 6 7 8

"total.tx t""total.tx t"

"heragu1.txt"

Present Heragu etal. Measured

Wavelength (µm)

Inte

nsity

(W/m

2 ⋅Sr⋅µm

)

Comparison of predicted infrared intensity(Plume + Nozzle)

0

50

100

150

200

250

300

350

400

450

500

1 2 3 4 5 6 7 8

"total.txt""total.txt""total.txt"

Plume radiation Nozzle radiation Total radiation

Wavelength (µm)

Inte

nsity

(W/m

2 ⋅Sr⋅µ

m)

predicted infrared intensity(Plume + Nozzle)

Validation of the Exhaust Plume Simulation

Validation of the Exhaust Plume Simulation

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14 16 18 20

"irr_5km.out"

Wavelength (µm)

Spec

tral I

nten

sity

(W⋅m

-2⋅S

r-1⋅µ

m-1

)

H2O

CO2, CO

H2O, CO2

CO2

Spectral radiant intensity of aircraft plume

Plume emissive bands absorbed by the atmosphere

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 12 14 16 18 20

"temp.txt""temp.txt"

Non

-dim

ensi

onal

ised

plu

me

inte

nsity

/Atm

. tra

ns

Atm. TransPlume intensityAtm. TransPlume intensity

Exhaust Plume Solver Validation

Wavelength (µm)

2 2.5 3.0 3.5 4.0 4.5 5.0 5.50

25

50

75

100

Rel

ativ

e S

pect

ral I

nten

sity

(-)

La Rocca, A. J., “Artificial Sources,”The Infrared Handbook, 1985

Spectral intensity from airc`raft plume for Boeing passenger aircraft

Wavelength (µm)

0

5

10

15

20

25

30

35

40

45

2 2.5 3 3.5 4 4.5 5 5.5 6

"irr_5km.out"

Plume spectral radiant intensity as transmitted by atmosphere

Lock-on Range due to the Plume

5km

0º (Horizon)180º SAM

90º (Zenith)

Mission

0 2 4 6

1

2

3

4

5

6

7

Wavelength (µm)

Lock

on

Ran

ge (k

m)

Lock-on Range due to Plume Radiation

• A comprehensive methodology is presented to model the IR signature produced by the aircraft exhaust plume and to evaluate its susceptibility against an IR guided SAM.

• The results qualitatively match well with the results available in the literature.

• The prominent band for plume radiation are centered around 2.7 µm, 4.3 µm, 5.5 µm, 6.5 and 15 µm due to the emission by CO2 , CO and H2O present in the plume.

• Since the exhaust plume and the atmosphere have same radiative participating species, namely H2O, CO2, & CO, most of the IR radiation emitted by the plume is absorbed in the intervening atmosphere.

• Only the radiation emitted from the broadened wings of the plume emissive bands prominent in the 4.15-4.2 µm band reaches the missile IR detector in the non after burning mode.

• The aircraft is susceptible to ground based IR guided SAMs due to the radiation emitted by its plume.

Exhaust Plume Dilution and Mixing for Bell 205 Aircraft

Todda Rabba

Infrared Signature Suppression

AIRCRAFT

F117-A, Night hawk

Exhaust pipe of F-117A

F117 Nozzle Configuration for IR Signature Reduction

Schematic of the basic Centre Body Tailpipe used on Bell 205 (UH-1H)

Bell 205 using Infrared Flares to deceive an incoming IR missile

Exhaust Plume Dilution and Mixing for Bell 205 Aircraft