Multimodal shape oscillations of droplets excited by an air stream

Deepu, P and Basu, Saptarshi and Kumar, Ranganathan (2014) Multimodal shape oscillations of droplets excited by an air stream. In: CHEMICAL ENGINEERING SCIENCE, 114 . pp. 85-93.

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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.

Item Type:	Journal Article
Publication:	CHEMICAL ENGINEERING SCIENCE
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Additional Information:	Copyright for this article belongs to the PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND
Keywords:	Pendant droplet; Shape oscillations; Vibrational modes; Fluid viscosity
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	11 Aug 2014 04:34
Last Modified:	11 Aug 2014 04:34
URI:	http://eprints.iisc.ac.in/id/eprint/49530

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