Title

Multimodal shape oscillations of droplets excited by an air stream

Authors

Authors

P. Deepu; S. Basu;R. Kumar

Comments

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Abbreviated Journal Title

Chem. Eng. Sci.

Keywords

Pendant droplet; Shape oscillations; Vibrational modes; Fluid viscosity; COUPLED OSCILLATIONS; SESSILE DROPS; DYNAMICS; VIBRATIONS; RAINDROPS; BEHAVIOR; CONTACT; BUBBLES; MOTIONS; SPHERES; Engineering, Chemical

Abstract

The shape dynamics of droplets exposed to an air jet at intermediate droplet Reynolds numbers is investigated. High speed imaging and hot-wire anemometry are employed to examine the mechanism of droplet oscillation. The theory that the vortex shedding behind the droplet induces oscillation is examined. In these experiments, no particular dominant frequency is found in the wake region of the droplet. Hence the inherent free-stream disturbances prove to be driving the droplet oscillations. The modes of droplet oscillation show a band of dominant frequencies near the corresponding natural frequency, further proving that there is no particular forcing frequency involved. In the frequency spectrum of the lowest mode of oscillation for glycerol at the highest Reynolds number, no response is observed below the threshold frequency corresponding to the viscous dissipation time scale. This selective suppression of lower frequencies in the case of glycerol is corroborated by scaling arguments. The influence of surface tension on the droplet oscillation is studied using ethanol as a test fluid. Since a lower surface tension reduces the natural frequency, ethanol shows lower excited frequencies. The oscillation levels of different fluids are quantified using the droplet aspect ratio and correlated in terms of Weber number and Ohnesorge number. (C) 2014 Elsevier Ltd. All rights reserved.

Journal Title

Chemical Engineering Science

Volume

114

Publication Date

1-1-2014

Document Type

Article

Language

English

First Page

85

Last Page

93

WOS Identifier

WOS:000337875200009

ISSN

0009-2509

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