Multimodal shape oscillations of droplets excited by an air stream

    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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