An Analytical Study on the Mechanism of Grouping of Droplets

Vaikuntanathan, Visakh; Ibach, Matthias; Arad, Alumah; Chu, Xu; Katoshevski, David; Greenberg, J.B.

doi:10.3390/fluids7050172

Cited by 3 publications

(1 citation statement)

References 41 publications

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“…The latter phenomenon was elucidated using a Stokes flow description of two spheres, incorporating hydrodynamic interaction and a perturbative term to account for finite inertial effects. In a recent study, Vaikuntanathan et al [7] systematically investigated the droplet grouping phenomenon and its mechanism in a stream of droplets. They observed that the leading droplet experiences a higher drag force compared to the trailing one, which forces droplets to group together and coalesce eventually.…”

Section: Introductionmentioning

confidence: 99%

Effect of Acoustics on Droplet Grouping Behaviour in a Single Stream of Droplets

Kumar,

Vaikuntanathan,

Ibach

et al. 2024

J. Phys.: Conf. Ser.

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Droplet and particle grouping can be influenced by applying an acoustic field and have practical applications such as particle scavenging and aerosol filters of engine exhaust and air purifiers. The present work experimentally investigates the influence of a standing acoustic wave on a single stream of droplets. The experimental setup consists of an acoustic transducer and a reflector plate through which the droplet stream passes in the presence or absence of an external pressure field generated by a standing acoustic wave. A droplet stream is generated with the help of a nozzle connected to a pressurized working fluid supply and piezoelectric transducer to control the spacing between droplets. The effect of the acoustic pressure field on the droplet stream generated by the nozzle operated at different piezoelectric excitation frequencies and fluid pressures is investigated. Droplet stream characteristics at every nozzle excitation frequency are observed with a high-speed camera when the acoustic field is switched OFF and ON. The competing effect of nozzle excitation frequency and acoustic field is observed. At lower nozzle frequencies, the nozzle generates an unstable stream of droplets having different sizes and spacings between them. When the acoustic field is applied at these lower frequencies, the stream of droplets becomes organized, and in some cases, it becomes equispaced and of the same size. However, an opposite behavior is observed at higher frequencies. In these cases, as the acoustic field is applied, an equispaced mono-disperse droplet stream becomes unstable due to the coalescence of droplets within the stream.

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Section: Introductionmentioning

confidence: 99%

Effect of Acoustics on Droplet Grouping Behaviour in a Single Stream of Droplets

Kumar,

Vaikuntanathan,

Ibach

et al. 2024

J. Phys.: Conf. Ser.

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The interfacial modes and modal causality in a dispersed bubbly turbulent flow

et al. 2023

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While data-driven analysis has demonstrated significant success in single-phase flow systems, its application to multi-phase flows has been relatively limited with fewer examples. In this study, we present a modal analysis and modal causality analysis of dispersed bubbly turbulent flow, with the aim of providing new insights into the interfacial gas–liquid interaction. Our study employs an in-house coupled level-set volume-of-fluid solver, which is combined with a modified fast Fourier transforms algorithm to perform interface-resolved direct numerical simulations in a turbulent channel flow with 96 bubbles occupying 5.4% volume. In the downward flow orientation, we observe that bubbles are mainly clustered in the channel center, producing pseudo-turbulence with isotropic characteristics. We apply the proper orthogonal decomposition method to the phase-resolved, three-dimensional velocity field, radius of the bubble as well as the surface tension force in order to extract the dominant modes. Notably, our results reveal the presence of two energetic modes in both the gas and liquid phases, as well as the interface, namely, the vortex-ring mode and the quadrupolar mode. We further investigate the causal relationship across the gas–liquid interface using the modal information transfer entropy. Our findings demonstrate a strong causality between the gas phase and the surface tension, whereas the causality between the liquid phase and surface tension is comparatively weak due to the multi-scale characteristics of the turbulent fields. Overall, our novel approach to investigating the interfacial gas–liquid interaction in dispersed bubbly turbulent flow provides valuable insights that enhance physical understanding and could lead to improved flow control and efficiency in a range of industrial processes. The identification of previously unidentified energetic modes using the POD method has the potential to advance research in this field, with potential implications for future design of control strategies in complex systems.

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An investigation of anisotropy in the bubbly turbulent flow via direct numerical simulations

Zhang,

Liu,

Wang

et al. 2024

Physics of Fluids

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We investigated the effects of bubble count, flow direction, and Eötvös number on deformable bubbles in turbulent channel flow. For a given shear Reynolds number Re = 180 and fixed bubble volume fractions (1.263% and 2.525%), we conducted a series of direct numerical simulations using a coupled level-set and volume-of-fluid solver to evaluate their impact on bubble volume fraction distribution, velocity fields, and turbulence characteristics. Each aspect was studied based on the microscopic equations of two-phase flow, and the accuracy of the modeling terms used in current Reynolds-averaged Navier–Stokes equation (RANS) models was assessed. The influence on the anisotropic state was analyzed using the Lumley triangle, and the anisotropy of Reynolds stresses was captured through the exact balance equations. The results indicate that in upward flow, bubbles tend to accumulate near the wall, with smaller Eötvös numbers leading to closer proximity to the wall and greater attenuation of the liquid-phase velocity. This distribution enhances energy dissipation and turbulence isotropy. In downward flow, bubbles cluster in the channel center, generating additional pseudo-turbulence and attenuating energy in the buffer layer. Moreover, the interfacial transfer of turbulent energy, as currently modeled in RANS, is found to be inadequate for upward flows.

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An Analytical Study on the Mechanism of Grouping of Droplets

Cited by 3 publications

References 41 publications

Effect of Acoustics on Droplet Grouping Behaviour in a Single Stream of Droplets

Effect of Acoustics on Droplet Grouping Behaviour in a Single Stream of Droplets

The interfacial modes and modal causality in a dispersed bubbly turbulent flow

An investigation of anisotropy in the bubbly turbulent flow via direct numerical simulations

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