Intensified and attenuated waves in a microbubble Taylor–Couette flow

Watamura, Tomoaki; Tasaka, Yuji; Murai, Yuichi

doi:10.1063/1.4804392

Cited by 21 publications

(21 citation statements)

References 47 publications

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“…With the help of particle tracking velocimetry (PTV) Yoshida et al (2009) studied the relationship between the observed drag reduction and changes in the vortical structures of the bubbly TC system. More recently Watamura et al (2013) investigated the effect of micro-bubbles on the properties of azimuthal waves found in TC flow ( Re i max =1000). Fokoua et al (2015) performed experiments on a small gap width (η = 0.91) two-phase TC system to study the correlation between bubble arrangement, wavelength of the Taylor vortices, and torque modification.…”

Section: Dr =mentioning

confidence: 99%

Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach

et al. 2016

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Two-phase turbulent Taylor-Couette (TC) flow is simulated using an Euler-Lagrange approach to study the effects of a secondary phase dispersed into a turbulent carrier phase (here bubbles dispersed into water). The dynamics of the carrier phase is computed using Direct Numerical Simulations (DNS) in an Eulerian framework, while the bubbles are tracked in a Lagrangian manner by modelling the effective drag, lift, added mass and buoyancy force acting on them. Two-way coupling is implemented between the dispersed phase and the carrier phase which allows for momentum exchange among both phases and to study the effect of the dispersed phase on the carrier phase dynamics. The radius ratio of the TC setup is fixed to η=0.833, and a maximum inner cylinder Reynolds number of Re i =8000 is reached. We vary the Froude number (F r), which is the ratio of the centripetal to the gravitational acceleration of the dispersed phase and study its effect on the net torque required to drive the TC system.For the two-phase TC system, we observe drag reduction, i.e., the torque required to drive the inner cylinder is less compared to that of the single phase system. The net drag reduction decreases with increasing Reynolds number Re i , which is consistent with previous experimental findings ( Murai et al. 2005Murai et al. , 2008. The drag reduction is strongly related to the Froude number: for fixed Reynolds number we observe higher drag reduction when F r < 1 than for with F r > 1. This buoyancy effect is more prominent in low Re i systems and decreases with increasing Reynolds number Re i . We trace the drag reduction back to the weakening of the angular momentum carrying Taylor rolls by the rising bubbles. We also investigate how the motion of the dispersed phase depends on Re i and F r, by studying the individual trajectories and mean dispersion of bubbles in the radial and axial directions. Indeed, the less buoyant bubbles (large F r) tend to get trapped by the Taylor rolls, while the more buoyant bubbles (small Fr) rise through and weaken them.

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Section: Dr =mentioning

confidence: 99%

Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach

et al. 2016

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“…For this particular regime, such reduction is rather linked to an inhomogeneity of the bubble distribution, following the waviness motion, this leading to a stabilization of the flow, as if the effective Reynolds number were decreased 6 .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…The research into this topic is also motivated by the knowledge that microbubbles show regularized motion in terms of their slip velocity, while larger bubbles show turbulence-like complex motion to result in a diffusion process. A similar focus was reported by Watamura et al (2013), who found preferential concentrations of microbubbles in Taylor-Couette flows, e.g., a negative diffusion coefficient for microbubbles in a shear flow. This microbubble physics may potentially be applied widely to mass, momentum, and heat transfer processes in chemical and mechanical engineering.…”

Section: Introductionmentioning

confidence: 53%

Pulsatory rise of microbubble swarm along a vertical wall

Kitagawa¹,

Murai²

2014

Chemical Engineering Science

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Based on the experimental finding that microbubble swarms dramatically promote heat transfer from a vertical heated wall, despite their potentially adiabatic nature, tests of microbubble fluid mechanics in the isothermal state are performed to clarify the unique motion characteristics of microbubble swarms. At constant bubble flow rate, the microbubble swarm shows a significant pulsatory rise along a vertical flat wall, particularly for small bubbles. Particle tracking velocimetry applied to the microbubbles shows that a two-way interaction between the microbubbles and the liquid flow self-excites the pulsation during their co-current rise. The sequence consists of the following processes: i) increase in the bubble number density close to the wall as a result of the liquid velocity gradient driven by the microbubbles themselves; ii) wave generation inside the microbubble swarm to induce the pulsatory rise of the swarm; and iii) amplification of the waves, which results in void-bursting motion in the final stage.

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Intensified and attenuated waves in a microbubble Taylor–Couette flow

Cited by 21 publications

References 47 publications

Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach

Drag reduction in numerical two-phase Taylor–Couette turbulence using an Euler–Lagrange approach

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

Pulsatory rise of microbubble swarm along a vertical wall

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