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Experiments in Fluids

, Volume 48, Issue 4, pp 615–629 | Cite as

Planar fluorescence for round bubble imaging and its application for the study of an axisymmetric two-phase jet

  • Yerbol K. Akhmetbekov
  • Sergey V. Alekseenko
  • Vladimir M. Dulin
  • Dmitriy M. Markovich
  • Konstantin S. Pervunin
Research Article

Abstract

A correlation-based processing algorithm for bubble identification by a planar fluorescence for bubble imaging (PFBI) technique is presented in this paper. The algorithm includes procedures to identify bubble positions and sizes, as well as to track bubbles and correct bubble displacement vectors. Moreover, several schemes for calculation time optimisation were realised to achieve a reliable calculation time. The developed algorithm identifies and tracks overlapping bubble images or images with non-uniform intensity distributions. The employed correlation and iterative passing approach provides sub-pixel accuracy of bubble displacement estimation. In addition, the presented algorithm for bubble ring detection can be easily applied to shadow photography images of bubbles, after the application of a derivative filter. The PFBI technique, combined with the particle image velocimetry and particle tracking velocimetry algorithms, was applied for the experimental study of bubbly free jet two-phase flows at Re = 12,000. Four cases of volumetric gas content in the jet core were studied: 0, 1.2, 2.4 and 4.2%, with the same mean bubble diameter—0.85 mm. The developed technique measures two-dimensional distributions of instantaneous void fractions, as well as both gaseous and liquid-phase velocities. Consequently, the mean void fraction and velocity fields and a set of second-order statistical moments were obtained, including correlations of void fraction and velocity pulsations. It was shown that the increase in volumetric gas content leads to the suppression of liquid-phase velocity fluctuations in the jet mixing layer.

Keywords

Void Fraction Bubble Velocity Bubble Image Bubble Ring Bubble Position 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

Re

Reynolds number

C

Correlation coefficient

I

Image intensity distribution

Im

Mask intensity distribution

m

Interrogation area width (pix)

n

Interrogation area height (pix)

rring

Mask ring radius (pix)

σring

Spread of mask ring rim (pix)

epsx, epsy

Mask centre position (pix)

Nr

Representative number of mask sectors

Nt

Total number of mask sectors

α

Local mean void fraction (%)

χb

Instantaneous void fraction (%)

d

Diameter of nozzle exit (m)

db

Average bubble diameter (m)

U0

Mean flow rate velocity (m/s)

β

Volumetric gas content (%)

r, θ, z

Radial, azimuthal and axial directions of the flow

V, W, U

Radial, azimuthal and axial components of the mean velocity (m/s)

υ, w, u

Radial, azimuthal and axial components of the fluctuating velocity (m/s)

\( \langle \rangle \)

Ensemble averaging operator

l

Subscript denotes liquid phase

b

Subscript denotes gas phase

Notes

Acknowledgments

This work was supported by the integration research projects of the Russian Academy of Sciences and the Russian Foundation for Basic Research.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Yerbol K. Akhmetbekov
    • 1
    • 2
  • Sergey V. Alekseenko
    • 1
    • 2
  • Vladimir M. Dulin
    • 1
  • Dmitriy M. Markovich
    • 1
    • 2
  • Konstantin S. Pervunin
    • 1
  1. 1.Siberian Branch of RAS, Institute of ThermophysicsNovosibirskRussia
  2. 2.Novosibirsk State UniversityNovosibirskRussia

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