Experiments on the motion of gas bubbles in 
turbulence generated by an active grid

Poorte, R.E.G.; Biesheuvel, A.

doi:10.1017/s0022112002008273

Cited by 135 publications

(125 citation statements)

References 33 publications

Supporting

Mentioning

117

Contrasting

Order By: Relevance

“…This anisotropy is not inherent in the carrier flow [44] and therefore suggests the role of gravity [30]. We note that with decreasing Re λ , the ratio of turbulent to gravitational acceleration, a η /g, decreases in our experiments (Table.…”

Section: Fig 1: (A)mentioning

confidence: 51%

Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration

Mathai¹,

Calzavarini²,

Brons³

et al. 2016

Phys. Rev. Lett.

View full text Add to dashboard Cite

We report on the Lagrangian statistics of acceleration of small (sub-Kolmogorov) bubbles and tracer particles with Stokes number St ≪1 in turbulent flow. At decreasing Reynolds number, the bubble accelerations show deviations from that of tracer particles, i.e. they deviate from the Heisenberg-Yaglom prediction and show a quicker decorrelation despite their small size and minute St. Using direct numerical simulations, we show that these effects arise due the drift of these particles through the turbulent flow. We theoretically predict this gravity-driven effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle driftvelocity governing the enhancement of acceleration variance and the reductions in correlation time and intermittency. Our predictions are in good agreement with experimental and numerical results. The present findings are relevant to a range of scenarios encompassing tiny bubbles and droplets that drift through the turbulent oceans and the atmosphere. They also question the common usage of micro-bubbles and micro-droplets as tracers in turbulence research.Heavy and light particles caught up in turbulent flows often behave differently from fluid tracers. The reason for this is usually the particle's inertia, which can drive them along trajectories that differ from those of the surrounding fluid elements [1][2][3][4]. Due to their inertia, measured by the Stokes number St 1 , such particles depart from fluid streamlines and distribute nonhomogeneously even when the carrier flow is statistically homogeneous [3,[5][6][7][8][9][10][11]). Numerical studies have captured several interesting effects of particle inertia through point-particle simulations in homogeneous isotropic turbulence [7,[12][13][14]. For instance, with increasing inertia, light particles showed an initial increase in acceleration variance (up to a value a 2 ∼ 9 times the tracer value) followed by a decrease, while heavy particles showed a monotonic trend of decreasing acceleration variance [15]. Such modifications of acceleration statistics arose primarily from the slow temporal response of these inertial particles, i.e when St was finite [9,[16][17][18][19]. In comparison, a lower limit of inertia can be imagined (St ≪ 1), when the particles respond to even the quickest flow fluctuations and, hence, are often deemed good trackers of the turbulent flow regardless of their density ratio [3,15,16,20]. The widespread use of small bubbles and droplets in flow visualization and particle tracking setups (e.g. Hydrogen bubble visualization and droplet-smoke-generators) is founded on this one assumption − that St ≪ 1 renders a particle responsive to the fastest fluctuations of the flow [21][22][23][24][25].In many practical situations, particles are subjected 1 Stokes number, St ≡ τp/τη , where τp is the particle response time, and τη is the Kolmogorov time scale of the flow.to body forces, typically gravitational or centrifugal [26]. This can be the case for rain droplets and aerosols set...

show abstract

Section: Fig 1: (A)mentioning

confidence: 51%

Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration

Mathai¹,

Calzavarini²,

Brons³

et al. 2016

Phys. Rev. Lett.

View full text Add to dashboard Cite

show abstract

“…In another protocol, also the velocity is picked randomly from a uniform distribution. 8 In the protocol of Mydlarski and Warhaft, 7 the axes are not rotated continuously, but their angles are flipped randomly. The influence of these simple protocols on the properties of the generated turbulence has been studied by Poorte and Biesheuvel.…”

Section: Introductionmentioning

confidence: 99%

“…The influence of these simple protocols on the properties of the generated turbulence has been studied by Poorte and Biesheuvel. 8 Protocols involving correlated random numbers to mimic the large-scale fluctuations of atmospheric turbulence were used by Knebel, Kittel, and Peinke. 10 An active grid offers the possibility to locally act on the flow.…”

Section: Introductionmentioning

confidence: 99%

Stirring turbulence with turbulence

2015

View full text Add to dashboard Cite

We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the largest eddies of the wind-tunnel turbulence. A large mismatch of these times creates a highly intermittent random flow with interesting but quite anomalous statistics.

show abstract

“…The major role played by coherent structures in a fully turbulent flow was emphasized by Sene et al 7 and Poorte and Biesheuvel. 8 Understanding the accumulation process is a key step toward predicting bubbleinduced modifications of the carrying fluid flow. Indeed, a small amount of dispersed phase located in the core of vortices can induce dramatic changes in the vortex structure.…”

Section: Introductionmentioning

confidence: 99%

Preferential accumulation of bubbles in Couette-Taylor flow patterns

Climent

Simonnet²,

Magnaudet

2007

Physics of Fluids

View full text Add to dashboard Cite

We investigate the migration of bubbles in several flow patterns occurring within the gap between a rotating inner cylinder and a concentric fixed outer cylinder. The time-dependent evolution of the two-phase flow is predicted through three-dimensional Euler-Lagrange simulations. Lagrangian tracking of spherical bubbles is coupled with direct numerical simulation of the Navier-Stokes equations. We assume that bubbles do not influence the background flow ͑one-way coupling simulations͒. The force balance on each bubble takes into account buoyancy, added-mass, viscous drag, and shear-induced lift forces. For increasing velocities of the rotating inner cylinder, the flow in the fluid gap evolves from the purely azimuthal steady Couette flow to Taylor toroidal vortices and eventually a wavy vortex flow. The migration of bubbles is highly dependent on the balance between buoyancy and centripetal forces ͑mostly due to the centripetal pressure gradient͒ directed toward the inner cylinder and the vortex cores. Depending on the rotation rate of the inner cylinder, bubbles tend to accumulate alternatively along the inner wall, inside the core of Taylor vortices or at particular locations within the wavy vortices. A stability analysis of the fixed points associated with bubble trajectories provides a clear understanding of their migration and preferential accumulation. The location of the accumulation points is parameterized by two dimensionless parameters expressing the balance of buoyancy, centripetal attraction toward the inner rotating cylinder, and entrapment in Taylor vortices. A complete phase diagram summarizing the various regimes of bubble migration is built. Several experimental conditions considered by Djéridi, Gabillet, and Billard ͓Phys.

show abstract

Experiments on the motion of gas bubbles in turbulence generated by an active grid

Cited by 135 publications

References 33 publications

Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration

Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration

Stirring turbulence with turbulence

Preferential accumulation of bubbles in Couette-Taylor flow patterns

Contact Info

Product

Resources

About