Experiments in Fluids

, Volume 19, Issue 3, pp 150–158 | Cite as

An efficient optical pressure measurement in compressible flows: Laser-induced iodine fluorescence

  • F. Lemoine
  • B. Leporcq
Originals

Abstract

The understanding of complex phenomena, the experimental validation of calculation codes, and the construction of data bases in fluid mechanics require the development of non-intrusive experimental techniques. The laser-induced fluorescence of a gaseous molecule seeded into a gas flow can be related to the flowfield thermodynamic parameters, such as pressure and temperature. An experimental method is described, that allows the removal of the temperature dependence of the fluorescence signal. A narrow-bandwidth single-line laser is tuned to the center of an absorption line, whose temperature dependence of the Boltzmann fraction can be neglected. The experimental set-up requires a single-line dye laser and a high resolution spectral analysis device.

The accuracy of the method, checked in a static vessel, appears to be better than 5%. The method has been successfully tested with a supersonic jet issuing from an underexpanded nozzle.

The experimental results have been compared to those of an Euler calculation. A mean difference of 14% has been observed, but a major part of this can be attributed to the difference between inviscid and real gas calculation.

List of Symbols

A21

spontaneous emission Einstein coefficient

Bv

rotational energy of the J level for the v vibrational level

Be

first order approximation of Bv

c

velocity of light

Copt

optical constant

E(v)

vibrational energy of the v level

f1

Boltzmann fraction

FCFi

Franck-Condon factor of the ith line

fv

vibrational fraction

tfr

rotational fraction

g

efficient spectral power density

h

Planck constant

I2X

iodine molecule in the X state

I2B

iodine molecule in the B state

[I2X]

molecular concentration of I2X

[I2B]

molecular concentration of I2B

Ii

relative intensity of the ith absorption line

J

rotational level of the fundamental state

J

rotational level of the excited state

k

Boltzmann constant

kc

collisional broadening coefficient

m

iodine molecular mass

n0

initial concentration of iodine in the absorbing state

P

pressure

Plaser

laser power

Pl(v)

laser power spectral density

Psl2

iodine vapor pressure

Q

quenching rate

Qv

vibrational partition function

T

temperature

v

vibrational level of the fundamental state

v

vibrational level of the excited state

Vc

collection volume

Xl2

iodine molar fraction

λ

wave length

ΔvD

Doppler linewidth, at half maximum

Δvc

collisional linewidth at half maximum

Vl

laser frequency

δ(v)

Dirac function

Δvi

spectral location of a line, referenced to the laser frequency

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References

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • F. Lemoine
    • 1
  • B. Leporcq
    • 1
  1. 1.Office National d'Etudes et de Recherches AérospatialeInstitut de Mécanique des Fluides de LilleLille CedexFrance

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