Nonspherical liquid droplet falling in air

Shapes and paths of an air bubble rising inside a liquid are investigated experimentally. About three hundred experiments are conducted in order to generate a phase plot in the Galilei and Eötvös numbers plane, which separates distinct regimes in terms of bubble behaviour. A wide range of the Galilei and Eötvös numbers are obtained by using aqueous glycerol solutions of different concentrations as the surrounding fluid, and by varying the bubble size. The dynamics is investigated in terms of shapes, topological changes and trajectories of the bubbles. Direct numerical simulations are conducted to study the bubble dynamics, which show excellent agreement with the experiments. To the best of our knowledge, this is the first time an experimentally obtained phase plot showing the distinct behaviour of an air bubble rising in a quiescent medium is reported for such a large range of Galilei and Eötvös numbers.

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“…12(b). On a separate note, it is mentioned here that a liquid drop falling in air (µ r = 57 and ρ r = 1000) never does wobbling motion [25].…”

Section: Effect Of Viscosity and Density Ratiosmentioning

confidence: 76%

Shapes and paths of an air bubble rising in quiescent liquids

et al. 2017

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“…Because of these additional complexities, there is no general analytical solution for the problem and numerical approaches are required to solve the governing equations [4][5][6]38 . Owing to the similar dynamics between a falling drop and a rising bubble, these two cases are often discussed together (see for example Ern et al 39 ), although fundamental difference between these two cases exists 38 .…”

Section: Dynamics Of a Falling Dropmentioning

confidence: 99%

“…Extensive numerical studies have been conducted to simulate the drop formation process by the volume-of-fluid (VOF) method, see for example Zhang 42 and Gueyffier et al 43 . The recent simulations by Agrawal et al 5 have used the VOF method to resolve the oscillation of a falling drop with a non-spherical initial shape. It is shown that the oscillation only arises in the longitudinal direction and no azimuthal variation was observed even when vortex shedding occurs in the wake of the drop.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…Nevertheless, despite its importance, the effect of drop formation on the subsequent oscillation and falling dynamics have not received enough attention in former studies. Instead of using the precise post-drop-formation state, ad hoc initial conditions (such as simple spheroid shape), are often used in simulations [4][5][6] . To fully incorporate the effect of drop formation, the whole process starting from drop growth, continuing with detachment, and eventually fall, is considered in the present simulation.…”

Section: Introductionmentioning

confidence: 99%

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Short-term oscillation and falling dynamics for a water drop dripping in quiescent air

et al. 2019

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The short-term transient falling dynamics of a dripping water drop in quiescent air has been investigated through both simulation and experiment. A representative case with a low inflow rate in the dripping regime is considered. The focus is on the short term behavior and the time range considered covers about eight dominant second-mode oscillations of the drop after it is formed. Due to the small fluid inertia at the inlet, the growth of the drop is quasi-static and is well captured by the static pendant drop theory. Nevertheless, it is demonstrated that the pinching dynamics and the resulting post-formation state of the drop trigger a nonlinear oscillation when the drop falls. The initial shape of the drop when it is just formed is decomposed into spherical harmonic modes. The initial mode amplitudes, characterized by the Fourier-Legendre coefficients, are found to be finite for up to the tenth mode. The pinching dynamics such as interface overturning introduces small-scale variation on the drop contour, which in turn contributes to the finite amplitudes of the higherorder modes. Furthermore, the initial kinetic energy when the droplet is just formed is as important as the initial surface energy contained in the drop shape, and is found to amplify the initial oscillation amplitude and to induce a phase shift in the oscillation of all the modes. By incorporating both the initial surface and kinetic energy, the linear model for a free drop oscillation yields very good predictions for the second and third modes. The mode amplitude spectra show both the primary frequencies that are consistent with the Lamb's theory and the secondary frequencies arising from different modes due to nonlinear inter-mode coupling. Moreover, it is worth to note that the nonlinear effect is most profound for the fourth mode owing to its resonant coupling with the dominant second mode. The complex transient flow inside and outside the drop is induced by the interaction between the falling motion and the nonlinear oscillation. The streamlines indicate that the internal flow is substantially different from the Hill vortex for a falling drop without oscillation.The temporal evolutions of both the internal flow and the wake morphology follow the dominant second oscillation mode. In the oblate-to-prolate deformation, the internal flow goes against the external flow. As a result, a saddle point arises in the drop, which gives rise to two counterrotating vortices. The vortex dynamics are visualized by the swirling-strength vortex identification criterion and the vorticity. Whereas the potential flow changes direction during a second-mode oscillation cycle, the rotating 2 directions of the vortices remain the same.

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“…A Span 80 (a lipophilic surfactant) with a hydrophilic-lipophilic balance (HLB) of 4.3 was used as the emulsifying agent to prepare 10% (v/v) water in diesel emulsion. A gravitational method [35][36][37] was used to characterize the stability of the emulsion. For this purpose, a mechanical stirrer running at 1000 rpm for 10 min was used to blend the emulsion, which was then stored in cylindrical tubs as shown in Figure 1.…”

Section: Emulsion Preparation Stability and Physical Propertiesmentioning

confidence: 99%

Investigation of Puffing and Micro-Explosion of Water-in-Diesel Emulsion Spray Using Shadow Imaging

et al. 2018

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Water-in-diesel emulsions potentially favor the occurrence of micro-explosions when exposed to elevated temperatures, thereby improving the mixing of fuels with the ambient gas. The distributions and sizes of both spray and dispersed water droplets have a significant effect on puffing and micro-explosion behavior. Although the injection pressure is likely to alter the properties of emulsions, this effect on the spray flow puffing and micro-explosion has not been reported. To investigate this, we injected a fuel spray using a microsyringe needle into a high-temperature environment to investigate the droplets’ behavior. Injection pressures were varied at 10% v/v water content, the samples were imaged using a digital microscope, and the dispersed droplet size distributions were extracted using a purpose-built image processing algorithm. A high-speed camera coupled with a long-distance microscope objective was then used to capture the emulsion spray droplets. Our measurements indicated that the secondary atomization was significantly affected by the injection pressure which reduced the dispersed droplet size and hence caused a delay in puffing. At high injection pressure (500, 1000, and 1500 bar), the water was evaporated during the spray and although there was not enough droplet residence time, puffing and micro-explosion were clearly observed. This study suggests that high injection pressures have a detrimental effect on the secondary atomization of water-in-diesel emulsions.

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Nonspherical liquid droplet falling in air

Cited by 39 publications

References 18 publications

Shapes and paths of an air bubble rising in quiescent liquids

Shapes and paths of an air bubble rising in quiescent liquids

Short-term oscillation and falling dynamics for a water drop dripping in quiescent air

Investigation of Puffing and Micro-Explosion of Water-in-Diesel Emulsion Spray Using Shadow Imaging

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