Effect of Single and Multiple Bubbles on a Thin Vortex Ring

Biswas, Subhajit; Govardhan, Raghuraman N.

doi:10.1615/jflowvisimageproc.2020031014

Cited by 7 publications

(3 citation statements)

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“…They also reported that, in the low-Weber-number case (lower than a critical value), the vortex core was fragmented when the bubble was trapped, with a simultaneous reduction in enstrophy and ring convection velocity. Similar processes of a bubble being trapped into a vortex ring as well as its subsequent azimuthal elongation and breakup have also been observed in more recent research (Biswas & Govardhan 2020), with both a single bubble and multiple bubbles considered. With a larger bubble, which is comparable to the vortex ring, experiments were performed with a major focus on the bubble breakup parameters, such as breakup frequency, number of daughter bubbles resulting from the breakup and the size distribution (Zednikova et al.…”

Section: Introductionsupporting

confidence: 77%

“…Although the two-way coupling between bubble and vortex ring has been considered in the previous studies mentioned above (Jha & Govardhan 2015; Zednikova et al. 2019; Biswas & Govardhan 2020), their major focus was still on the deformation and breakup of bubbles. It would be of interest to study the effect of bubbles on the characteristic properties of the vortex ring to extrapolate the results to more complex turbulent bubbly flows, as addressed by Martínez-Bazán (2015).…”

Section: Introductionmentioning

confidence: 99%

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Modification of flow transition for a vortex ring by a bubble released at the axis

2023

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The interactions between a vortex ring and a gas bubble released at the axis are studied numerically, which shed light on understanding more complicated bubble–turbulence coupling. We fix the Reynolds number at $Re_{\tau }=7500$ and consider various Weber numbers in the range of $We=130\unicode{x2013}870$ . We find that the translating speed of the vortex ring is substantially lower than the case of the vortex ring without a bubble. It is explained with two different mechanisms, depending on the Weber number. In the low- $We$ range, the reduction of translating speed of the ring is due to the capture of bubbles into the ring core, leading to significant changes in the vorticity distribution within the core. In the high- $We$ range, the repeatedly generated secondary vortex rings perturb the primary one, which bring about an earlier flow transition, thereby reducing the translating speed of the vortex ring. On the other hand, the evolution of a gas bubble is also affected by the presence of the vortex ring. In the low- $We$ range, we observe binary breakup of the bubble after it is captured by the primary vortex ring. In contrast, in the high- $We$ range, it is interesting to find that the bubble experiences sequentially stretching, spreading and breakup stages. In the high- $We$ range, the numbers of smaller bubbles predicted by the classical Rayleigh–Plateau instability of a stretched cylindrical bubble agree well with our numerical simulations. Consistent with the previous experiments, this number keeps unchanged at 16 as $We$ further increases. An additional comparison is made between two higher Reynolds numbers, indicating that the finer eddies in a vortical field with a higher Reynolds number tend to tear the bubble into more fragments.

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Section: Introductionsupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Modification of flow transition for a vortex ring by a bubble released at the axis

2023

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“…Several physical mechanisms are known to be involved in bubble drag reduction, e.g., the reduction in flow mixture density and reduced viscosity (Legner 1984;Skudarnov and Lin 2006;Elbing et al 2008), bubble deformability lifting the high vorticity regions away from the wall (Van Gils et al 2013;Lu et al 2005), effective compressibility of the flow mixture (Ferrante and Elghobashi 2004), disruption of the coherent flow structures by bubbles (Sugiyama et al 2008;Jha and Govardhan 2015;Biswas and Govardhan 2020, 2022, and the extraction of turbulent energy during bubble deformation and splitting (Meng and Uhlman 1989). These different mechanisms do not exclude each other and are likely to act simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Effects of salt concentration on top wall bubble injection in a turbulent channel flow: bubble dynamics and wall drag reduction

Biswas,

Govardhan

2024

Exp Fluids

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Most applications related to bubble drag reduction (BDR) occur in contaminated environments where the presence of different surface active agents modify bubble coalescence and hence, affect flow drag. Although there have been studies on bubble drag modifications with salt/surfactant, the effects of systematic variation in salt/surfactant concentration on bubble dynamics and drag remain relatively unexplored. Driven by this motivation, in the present work, we experimentally investigate the effects of salt concentration on the bubble dynamics and drag modification in a fully developed horizontal turbulent channel flow for top wall bubble injection, over a wide range of salt concentrations (0< M <0.08, moles/liter), channel Reynolds number (22,500< Re <65,000), and injected bubble void fraction (0< α <0.16). The injected bubbles interact with the flow in the turbulent channel and as they move downstream reach an equilibrium state between the bubbly phase and the fully developed carrier phase that persists further downstream. The equilibrium state of the bubble dynamics is captured by high-speed visualizations and the corresponding drag is obtained from stream-wise pressure drop measurements within the channel. Increasing salt concentration levels is seen to lead to reduction in bubble coalescence and consequently in bubble size that modifies bubble deformability, migration, and distribution near the top wall, with the changes being dependent on the Re and α values. At low Re ≈ 22, 500, the addition of salt leads to a dramatic reduction in bubble sizes (∼ 100 microns)

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Bubble Capture, Breakup, and Coalescence in Vortex–Bubble Interaction

Biswas

Govardhan

2021

Lecture Notes in Mechanical Engineering

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Effect of Single and Multiple Bubbles on a Thin Vortex Ring

Cited by 7 publications

References 0 publications

Modification of flow transition for a vortex ring by a bubble released at the axis

Modification of flow transition for a vortex ring by a bubble released at the axis

Effects of salt concentration on top wall bubble injection in a turbulent channel flow: bubble dynamics and wall drag reduction

Bubble Capture, Breakup, and Coalescence in Vortex–Bubble Interaction

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