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Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows

Publication ,  Journal Article
Bragg, AD; Liao, Y; Fröhlich, J; Ma, T
Published in: International Journal of Heat and Fluid Flow
October 1, 2021

There has been considerable discussion in recent years concerning whether a log-law exists for wall-bounded, turbulent bubbly flows. Previous studies have argued for the existence of such a log-law, with a modified von Kármán constant, and this is used in various modelling studies. We provide a critique of this idea, and present several theoretical reasons why a log-law need not be expected in general for wall-bounded, turbulent bubbly flows. We then demonstrate using recent data from interface-resolving Direct Numerical Simulations that when the bubbles make a significant contribution to the channel flow dynamics, the mean flow profile of the fluid can deviate significantly from the log-law behaviour that approximately holds for the single-phase case. The departures are not surprising and the basic reason for them is simple, namely that for bubbly flows, the mean flow is affected by a number of additional dynamical parameters, such as the void fraction, that do not play a role for the single-phase case. As a result, the inner/outer asymptotic regimes that form the basis of the derivation of the log-law for single-phase flow do not exist in general for bubbly turbulent flows. Nevertheless, we do find that for some cases, the bubbles do not cause significant departures from the unladen log-law behaviour. Moreover, we show that if departures occur these cannot be understood simply in terms of the averaged void fraction, but that more subtle effects such as the bubble Reynolds number and the competition between the wall-induced turbulence and the bubble-induced turbulence must play a role.

Duke Scholars

Published In

International Journal of Heat and Fluid Flow

DOI

ISSN

0142-727X

Publication Date

October 1, 2021

Volume

91

Related Subject Headings

  • Mechanical Engineering & Transports
  • 4012 Fluid mechanics and thermal engineering
  • 0915 Interdisciplinary Engineering
  • 0913 Mechanical Engineering
  • 0901 Aerospace Engineering
 

Citation

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ICMJE
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Bragg, A. D., Liao, Y., Fröhlich, J., & Ma, T. (2021). Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows. International Journal of Heat and Fluid Flow, 91. https://doi.org/10.1016/j.ijheatfluidflow.2021.108857
Bragg, A. D., Y. Liao, J. Fröhlich, and T. Ma. “Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows.” International Journal of Heat and Fluid Flow 91 (October 1, 2021). https://doi.org/10.1016/j.ijheatfluidflow.2021.108857.
Bragg AD, Liao Y, Fröhlich J, Ma T. Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows. International Journal of Heat and Fluid Flow. 2021 Oct 1;91.
Bragg, A. D., et al. “Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows.” International Journal of Heat and Fluid Flow, vol. 91, Oct. 2021. Scopus, doi:10.1016/j.ijheatfluidflow.2021.108857.
Bragg AD, Liao Y, Fröhlich J, Ma T. Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows. International Journal of Heat and Fluid Flow. 2021 Oct 1;91.
Journal cover image

Published In

International Journal of Heat and Fluid Flow

DOI

ISSN

0142-727X

Publication Date

October 1, 2021

Volume

91

Related Subject Headings

  • Mechanical Engineering & Transports
  • 4012 Fluid mechanics and thermal engineering
  • 0915 Interdisciplinary Engineering
  • 0913 Mechanical Engineering
  • 0901 Aerospace Engineering