Effect of bubble’s arrangement on the viscous torque in bubbly Taylor-Couette flow

Fokoua, Georges; Gabillet, Céline; Aubert, Adrien; Colin, Catherine

doi:10.1063/1.4915071

Cited by 20 publications

(30 citation statements)

References 26 publications

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“…Further downstream, turbulent diffusion causes bubbles to move away from the wall (Murai 2014). A similar mechanism was observed in Taylor-Couette flow, where strong secondary flows transport bubbles away from the inner cylinder, resulting in a decrease of DR (van den Berg et al 2007;Fokoua et al 2015;Verschoof et al 2018a).…”

Section: Bubbly Drag Reductionsupporting

confidence: 58%

Bubbly drag reduction using a hydrophobic inner cylinder in Taylor–Couette turbulence

et al. 2019

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In this study we experimentally investigate bubbly drag reduction in a highly turbulent flow of water with dispersed air at 5.0 × 10 5 Re 1.7 × 10 6 over a non-wetting surface containing micro-scale roughness. To do so, the Taylor-Couette geometry is used, allowing for both accurate global drag and local flow measurements. The inner cylinder -coated with a rough, hydrophobic material -is rotating, whereas the smooth outer cylinder is kept stationary. The crucial control parameter is the air volume fraction α present in the working fluid. For small volume fractions (α < 4 %), we observe that the surface roughness from the coating increases the drag. For large volume fractions of air (α 4 %), the drag decreases compared to the case with both the inner and outer cylinders uncoated, i.e. smooth and hydrophilic, using the same volume fraction of air. This suggests that two competing mechanisms are at place: on the one hand the roughness invokes an extension of the log-layer -resulting in an increase in drag -and on the other hand there is a drag-reducing mechanism of the hydrophobic surface interacting with the bubbly liquid. The balance between these two effects determines whether there is overall drag reduction or drag enhancement. For further increased bubble concentration α = 6 % we find a saturation of the drag reduction effect. Our study gives guidelines for industrial applications of bubbly drag reduction in hydrophobic wall-bounded turbulent flows.

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Section: Bubbly Drag Reductionsupporting

confidence: 58%

Bubbly drag reduction using a hydrophobic inner cylinder in Taylor–Couette turbulence

et al. 2019

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“…The left block of data are experiments and numerical simulations for microbubble drag reduction from refs. [214,215,222,223], and the right block of data are our large Re experiments with deformable bubbles [196,205,206].…”

Section: Effective Bubble Force Models Dispersed Bubbly Flow Anmentioning

confidence: 99%

Bubble puzzles: From fundamentals to applications

Lohse

2018

Phys. Rev. Fluids

143

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For centuries, bubbles have fascinated artists, engineers, and scientists alike. In spite of century-long research on them, new and often surprising bubble phenomena, features, and applications keep popping up. In this paper I sketch my personal scientific bubble journey, starting with single bubble sonoluminescence, continuing with sound emission and scattering of bubbles, cavitation, snapping shrimp, impact events, air entrainment, surface micro-and nanobubbles, and finally coming to effective force models for bubbles and dispersed bubbly two-phase flow. In particular, I also cover various applications of bubbles, namely in ultrasound diagnostics, drug and gene delivery, piezo-acoustic inkjet printing, immersion lithography, sonochemistry, electrolysis, catalysis, acoustic marine geophysical survey, and bubble drag reduction for naval vessels, and show how these applications crossed my way. I also try to show that good and interesting fundamental science and relevant applications are not a contradiction, but mutually stimulate each other in both directions.

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“…Bubbles can interact with these large-scale vortices. When the outer cylinder is at rest, the Taylor-Couette flow is thus one of the academic sheared flows that is suitable for investigating the effect of bubbles on the transition to turbulence of Newtonian liquid [5,6] and studying the bubbles interaction with the wall friction in a context of bubbly drag reduction [7][8][9]. For small Reynolds numbers and small Froude numbers, bubbles are accumulated uniformly along the inner cylinder and slide upward along the wall.…”

Section: Introductionmentioning

confidence: 99%

Defect-mediated turbulence in bubbly Taylor-Couette flow

et al. 2020

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We investigate experimentally the defect-mediated turbulence (DMT) which is induced by bubbles injection in a Taylor-Couette flow when the inner cylinder is rotating while the outer cylinder is fixed. Bubbles of 1.2 mm in diameter are injected at the bottom of a Taylor-Couette device of radii ratio equal to 0.91. The tangential Reynolds number range is [2 200, 19 300] and the air injection rate varies up to 800 ml/min. For these conditions of the experiments, bubbles are trapped in the gap by the Taylor vortices and arranged as patterns (toroidal, wavy toroidal, spirals, and wavy spirals). Visualizations of the bubble patterns were carried out. When decreasing the Reynolds number or increasing the air injection rate, spiral and toroidal patterns can coexist in a composite flow. Defects occur in the bubble's patterns (merging or splitting of the Taylor vortex pairs). By analyzing the space-time diagram of bubbles patterns and their complex demodulation, we highlight different regimes and transitions in the DMT of the bubbly Taylor-Couette flow. The control parameter of the transitions is the air volumetric fraction, which evolves as the ratio between the axial injection Reynolds number and the tangential Reynolds number. By increasing the air volumetric fraction, the defects in the DMT flows are classified as three flow regimes: (i) structured composite flow where the defects are periodic in space and time, (ii) intermittency defects chaos where the defects zones alternate randomly with the patterns in time and space, and (iii) developed defects chaos with a large defects density. The statistical properties of these three regimes of the DMT are analyzed in the framework of the complex Ginzburg-Landau equation.

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Effect of bubble’s arrangement on the viscous torque in bubbly Taylor-Couette flow

Abstract: is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible.

Cited by 20 publications

References 26 publications

Bubbly drag reduction using a hydrophobic inner cylinder in Taylor–Couette turbulence

Bubbly drag reduction using a hydrophobic inner cylinder in Taylor–Couette turbulence

Bubble puzzles: From fundamentals to applications

Defect-mediated turbulence in bubbly Taylor-Couette flow

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