Turbulence in the liquid phase of a uniform bubbly air–water flow

Lance, Michel; Bataille, J.

doi:10.1017/s0022112091001015

Cited by 490 publications

(368 citation statements)

References 25 publications

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“…Point (ii) constitutes a major difference since classic turbulence is unlikely to be able to maintain vertical homogeneity when upside-down symmetry is broken, non-zero dissymmetry coefficients being usually associated with a turbulence gradient (Risso & Fabre 1997). A second difference is that the spectral signature of bubble-induced turbulence differs from the classic K5/3 power law (Lance & Bataille 1991), indicating that the dynamics of the fluctuating eddies is different. The bubbleinduced turbulence is commonly considered as a turbulence in which energy is injected at an intermediate scale close to the bubble diameter instead of being supplied by the largest scales of the flow.…”

Section: Perspectivesmentioning

confidence: 99%

Wake attenuation in large Reynolds number dispersed two-phase flows

Risso

Roig

Amoura

et al. 2008

Phil. Trans. R. Soc. A.

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The dynamics of high Reynolds number-dispersed two-phase flow strongly depends on the wakes generated behind the moving bodies that constitute the dispersed phase. The length of these wakes is considerably reduced compared with those developing behind isolated bodies. In this paper, this wake attenuation is studied from several complementary experimental investigations with the aim of determining how it depends on the body Reynolds number and the volume fraction a. It is first shown that the wakes inside a homogeneous swarm of rising bubbles decay exponentially with a characteristic length that scales as the ratio of the bubble diameter d to the drag coefficient C d , and surprisingly does not depend on a for 10 K2 %a%10 K1 . The attenuation of the wakes in a fixed array of spheres randomly distributed in space (aZ2!10 K2 ) is observed to be stronger than that of the wake of an isolated sphere in a turbulent incident flow, but similar to that of bubbles within a homogeneous swarm. It thus appears that the wakes in dispersed two-phase flows are controlled by multi-body interactions, which cause a much faster decay than turbulent fluctuations having the same energy and integral length scale. Decomposition of velocity fluctuations into a contribution related to temporal variations and that associated to the random character of the body positions is proposed as a perspective for studying the mechanisms responsible for multi-body interactions.

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Section: Perspectivesmentioning

confidence: 99%

Wake attenuation in large Reynolds number dispersed two-phase flows

Risso

Roig

Amoura

et al. 2008

Phil. Trans. R. Soc. A.

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“…In this context, the description of the liquid agitation is a key issue. In the most general situation, such as that encountered in an industrial bubble column, the agitation has different sources: (1) the bubble-induced agitation that results from the flow disturbances generated by bubble motions (Lance & Bataille 1991;Cartellier & Rivière 2001;Zenit, Koch & Sangani 2001;Risso & Ellingsen 2002), (2) the buoyancy-driven recirculation cells that develop as soon as the volume fraction is not uniform (Climent & Magnaudet 1999;Mudde 2005), and (3) the turbulence produced by mean shear (Larue de Tournemine & Roig 2010;Prakash et al 2016). The present work focuses on the bubble-induced agitation at large Reynolds number, i.e.…”

Section: Introductionmentioning

confidence: 99%

Velocity fluctuations generated by the flow through a random array of spheres: a model of bubble-induced agitation

et al. 2017

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To cite this version:Zouhir Amoura, Cédric Besnaci, Frédéric Risso, Véronique Roig. Velocity fluctuations generated by the flow through a random array of spheres: a model of bubble-induced agitation. Journal of Fluid Mechanics, Cambridge University Press (CUP), 2017, 823, pp.592-616. <10.1017/jfm.2017 This work reports an experimental investigation of the flow through a random array of fixed solid spheres. The volume fraction of the spheres is 2 %, and the Reynolds number Re based on the sphere diameter and the average flow velocity is varied from 120 to 1040. Using time and spatial averaging, the fluctuations have been decomposed into two contributions of different natures: a spatial fluctuation that accounts for the strong inhomogeneity of the flow around each sphere, and a time fluctuation that comes from the instability of the flow at large enough Reynolds numbers. The evolutions of these two contributions with the Reynolds number are different, so that their relative importance varies. However, when each is normalized by using its own variance and the integral length scales of the fluctuations, their spectra and probability density functions (PDFs) are almost independent of Re. The spatial fluctuation mostly comes from the velocity deficit in the wakes of the spheres, and is thus dominated by scales larger than one or two sphere diameters. It is found to be responsible for the asymmetry of the PDFs of the vertical fluctuations and of the major part of the anisotropy level between the vertical and the horizontal components of the fluctuations. The time fluctuation dominates at scales smaller than the integral length scale. It is isotropic and its PDFs, well described by an exponential distribution, are non-Gaussian. The spectra of the spatial and the time fluctuations both show an evolution as the power −3 of the wavenumber, but not exactly in the same subrange. All these properties are found in remarkable agreement with the results of both experimental investigations and large eddy simulations (LES) of a homogeneous bubble swarm. This confirms that the main mechanism responsible for the production of bubble-induced fluctuations is the interaction of the velocity disturbances caused by obstacles immersed in a flow and that the structure of this agitation is weakly dependent on the precise nature of the obstacles. The understanding and the modelling of the agitation generated by the motion of a dispersed phase, such as the bubble-induced agitation, therefore require one to distinguish between the roles of these two contributions.

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“…Details of the database are provided in Table 1 smaller bubbles are included for downward flow conditions only (0.8 mm and 1.5 mm). In 299 addition, comparison is also provided against grid-generated turbulence data obtained for 300 bubbly flows by Lance and Bataille (1991). Since these data were only used for validating 301 predictions of the axial development of the turbulence, they are not included in Table 1 it is important to stress the necessity of detailed experimental studies for proper model 315 validation.…”

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confidence: 99%