Experimental characterization of the agitation generated by bubbles rising at high Reynolds number

Riboux, Guillaume; Risso, Frédéric; Legendre, Dominique

doi:10.1017/s0022112009992084

Cited by 167 publications

(294 citation statements)

References 22 publications

Supporting

Mentioning

242

Contrasting

Order By: Relevance

“…Once velocities are normalized by the standard deviation of the fluctuations and lengths by Λ, the structure of the liquid agitation turns out to be weakly dependent on the gas volume fraction. The agitation is anisotropic with a standard deviation of the vertical fluctuations that was found to be between 30 % and 50 % larger than that of the horizontal fluctuations by Riboux et al (2010). The PDFs (probability density functions) of the fluctuations do not follow a Gaussian distribution.…”

Section: Introductionmentioning

confidence: 92%

“…A relevant configuration to isolate the bubble-induced agitation from the other sources of fluctuations is the homogeneous swarm of rising bubbles. In recent years, several works have carried out experimental investigations of this configuration in order to characterize the properties of the bubble-induced agitation (Martinez-Mercado, Palacios-Morales & Zenit 2007;Roig & Larue de Tournemine 2007;Risso et al 2008;Martinez-Mercado et al 2010;Riboux, Risso & Legendre 2010;Mendez-Diaz et al 2013;Colombet et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…A description of the statistical properties of the bubble-induced agitation has been achieved by Riboux et al (2010) from measurements in a homogeneous swarm of ellipsoidal bubbles of diameter d between 1.6 and 2.5 mm rising in water (500 Re 800) at volume fraction α from 0.5 % to 10 %. Three physical quantities are required to determine the agitation.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2017

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…Lance & Bataille (1991) observed in their experiment a k −3 energy spectrum at intermediate scales (where k is the wavenumber). Riboux, Risso & Legendre (2010) considered a homogenous bubble swarm to investigate the influence of the bubble volume fraction on the velocity fluctuations and the extension of the k −3 spectrum. In the aforementioned papers, no clusters of bubbles are observed.…”

Section: Introductionmentioning

confidence: 99%

Turbulent thermal convection driven by heated inertial particles

et al. 2016

View full text Add to dashboard Cite

This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 18470Open Archive Toulouse Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. The heating of particles in a dilute suspension, for instance by radiation, chemical reactions or radioactivity, leads to local temperature fluctuations in the fluid due to the non-uniformity of the disperse phase. In the presence of a gravity field, the fluid is set in motion by the resulting buoyancy forces. When the particle density is different than that of the fluid, the fluid motion alters the spatial distribution of the particles and possibly strengthens their concentration inhomogeneities. This in turn causes more intense local heating. Direct numerical simulations in the Boussinesq limit show this feedback loop. Various regimes are identified depending on the particle inertia. For very small particle inertia, the macroscopic behaviour of the system is the result of many thermal plumes that are generated independently of each other. For significant particle inertia, clusters of particles are observed and their dynamics controls the flow. The emergence of very intermittent turbulent fluctuations shows that the flow is influenced by the larger structures (turbulent convection) as well as by the small-scale dynamics that affect particle segregation and thus the flow forcing. Assuming thermal equilibrium between the particles and the fluid (i.e. infinitely fast thermal relaxation of the particle), we investigate the evolution of statistical observables with the change of the main control parameters (namely the particle number density, the particle inertia and the domain size), and propose a scaling argument for these trends. Concerning the energy density in the spectral space, it is observed that the turbulent energy and temperature spectra follow a power law, the exponent of which varies continuously with the Stokes number. Furthermore, the study of the spectra of the temperature and momentum forcing (and thus of the concentration/temperature and velocity/temperature correlations) gives strong support to the proposed feedback loop mechanism. We then discuss the intermittency of the flow, and analyse the effect of relaxing some of the simplifying assumptions, thus assessing the relevance of the original studied configuration. To cite this version:

show abstract

“…[8][9][10] The agitation is important in situations of flows with non-dilute particle loading. 11 Transfer processes, such as dust resuspension (for particles), heat transfer (by vapor bubbles), or interfacial gas transfer across a free surface (e.g., bubbles) predominately arise from the significant agitation afforded by the movement of discrete elements close to boundaries. [12][13][14] The kinematic blocking motion caused by a boundary (such as a rigid wall or free surface) inhibits the effects of external turbulence (for instance, by convection or the ambient flow) moving fluid near boundaries.…”

Section: Introductionmentioning

confidence: 99%

Fluid velocity fluctuations in a collision of a sphere with a wall

et al. 2011

View full text Add to dashboard Cite

A study of thermal counterflow using particle tracking velocimetry Phys. Fluids 23, 107102 (2011) Particle accumulation on periodic orbits by repeated free surface collisions Phys. Fluids 23, 072106 (2011) We report on the results of a combined experimental and numerical study on the fluid motion generated by the controlled approach and arrest of a solid sphere moving towards a solid wall at moderate Reynolds number. The experiments are performed in a small tank filled with water for a range of Reynolds numbers for which the flow remains axisymmetric. The fluid agitation of the fluid related to the kinetic energy is obtained as function of time in the experiment in a volume located around the impact point. The same quantities are obtained from the numerical simulations for the same volume of integration as in the experiments and also for the entire volume of the container. As shown in previous studies, this flow is characterized by a vortex ring, initially in the wake of the sphere, that spreads radially along the wall, generating secondary vorticity of opposite sign at the sphere surface and wall. It is also observed that before the impact, the kinetic energy increases sharply for a small period of time and then decreases gradually as the fluid motion dies out. The measure of the relative agitation of the collision is found to increase weakly with the Reynolds number Re. The close agreement between the numerics and experiments is indicative of the robustness of the results. These results may be useful in light of a potential modelling of particle-laden flows. Movies illustrating the spatio-temporal dynamics are provided with the online version of this paper.

show abstract

Experimental characterization of the agitation generated by bubbles rising at high Reynolds number

Cited by 167 publications

References 22 publications

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

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

Turbulent thermal convection driven by heated inertial particles

Fluid velocity fluctuations in a collision of a sphere with a wall

Contact Info

Product

Resources

About