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Multiphase Science and Technology
SJR: 0.153 SNIP: 0.222 CiteScore™: 0.26

ISSN Imprimir: 0276-1459
ISSN On-line: 1943-6181

Multiphase Science and Technology

DOI: 10.1615/MultScienTechn.v22.i3.30
pages 211-232

EFFECTS OF BUBBLES ON TURBULENCE PROPERTIES IN A DUCT FLOW

Shigeo Hosokawa
Kobe University
Takashi Suzuki
Toyohashi University of Technology, Hibarigaoka 1-1, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
Akio Tomiyama
Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe, 657-8501, Japan

RESUMO

Influence of bubbles on turbulence properties depends on the ratio of bubble size dB to turbulence length scale lt and the ratio of relative velocity V R between bubbles and liquid to turbulence velocity v'. Since most studies on turbulent bubbly flow have been carried out for flows with large dB/ lt, little is known regarding the turbulence modulation in bubbly flows with small dB/ lt and large V R/ v'. Hence, turbulence properties are measured for bubbly flows with small dB/ lt and large V R/v' using a molecular tagging method based on a photobleaching reaction (PB-MTV). This method can measure not only velocity components but also the gradients by making use of the translation and deformation of a tag and enables us to evaluate the turbulence kinetic energy (TKE) budget. The experimental result indicates that the boundary between the linear sublayer and the log region shifts toward the wall by addition of bubbles in the buffer layer. The bubbles migrating toward the vicinity of the wall increase the liquid velocity gradient at the wall, that is, the shear-induced turbulence is enhanced in the near wall region. When the bubble size is comparable to the Kolmogorov scale, the influence of the bubble-induced pseudo turbulence on the TKE budget is not prominent, in spite of the large relative velocity. The expression of eddy viscosity used in the low-Reynolds-number k-ϵ model is applicable to the bubbly flows in which the bubble-induced pseudo turbulence is not prominent. The expression of eddy viscosity used in the standard k-ϵ model is also applicable, provided that accurate boundary conditions for frictional velocity, TKE, and dissipation rate of TKE are given.

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