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A laser Rayleigh scattering system for scalar transport studies

Abstract

A laser Rayleigh scattering system with software particle filtering has been developed for scalar transport studies in turbulent flows under isothermal and combusting conditions. The system was tested in the initial region of a Freon-12 (vapour) free jet by comparing mean concentrations of Freon-12 to those obtained with a sampling probe. When concentration fluctuations were low (< 15%) the agreement between the two methods was excellent but when both the concentration fluctuations and the number density of the ambient particles were high the Rayleigh system overestimated the mean concentration of Freon-12 by a maximum of 10%.

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Abbreviations

D 0 :

jet nozzle diameter

f 1 :

focal length of lens L i

f 2 :

focal length of lens L 2

f 3 :

focal length of lens L 3

I :

instantaneous light intensity

Ī :

mean light intensity

I′:

fluctuating light intensity

I B :

intensity of background light

I L :

intensity of laser light incident onto the scattering volume

I N :

intensity of electronic noise signal

I R :

intensity of Rayleigh signal

I T :

total intensity of scattered light

K :

calibration constant of Rayleigh optical system

N :

total number density of molecules

N i :

number density of species i

n i :

index of refraction of species i

X i :

mole fraction of species i

X :

ensemble-averaged mean concentration (mole fraction)

\(\tilde X\) :

ensemble-averaged r.m.s. of concentration fluctuations

x :

axial distance

θ s :

scattering angle

λ:

laser wavelength

σ Ri :

Rayleigh scattering cross-section of species i

Ω:

solid angle of collection optics

Δx :

length of scattering volume

Δy :

waist diameter of scattering volume

0:

reference condition

References

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Arcoumanis, C. A laser Rayleigh scattering system for scalar transport studies. Experiments in Fluids 3, 103–108 (1985). https://doi.org/10.1007/BF00276716

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Keywords

  • Sampling Probe
  • Transport Study
  • Initial Region
  • Concentration Fluctuation
  • Software Particle