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Atomization of acoustically forced liquid sheets

Published online by Cambridge University Press:  10 October 2019

Sandip Dighe Open the ORCID record for Sandip Dighe [Opens in a new window]  and
Hrishikesh Gadgil
Sandip Dighe*
Affiliation:
Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India
Hrishikesh Gadgil
Affiliation:
Department of Aerospace Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India
*
†Email address for correspondence: [email protected]
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Abstract

Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid jets and subjected to transverse acoustic forcing in quiescent ambient is investigated. The acoustic forcing perturbs the liquid sheet perpendicular to its plane, thereby setting up a train of sinuous waves propagating radially outwards from the impingement point. These sheet undulations grow as the wave speed decreases towards the edge of the sheet and the sheet characteristics, like intact length and mean drop size, reduce drastically as compared to the natural breakup. Our observations show that the effect of the acoustic field is perceptible over a continuous range of forcing frequencies. Beyond a certain forcing frequency, called the cutoff frequency, the effect of the external acoustic field ceases. The cutoff frequency is found to be an increasing function of the Weber number. Our measurements of the characteristics of spatially amplifying sinuous waves show that the instabilities responsible for the natural sheet breakup augment in the presence of external forcing. Combining the experimental observations and measurements, we conclude that the linear theory of aerodynamic interaction (Squire’s theory) (Squire, Brit. J. Appl. Phys., vol. 4 (6), 1953, pp. 167–169) predicts the important features of this phenomenon reasonably well.

JFM classification

Drops and Bubbles: Breakup/coalescence Interfacial Flows (free surface): Thin films
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 880 , 10 December 2019 , pp. 653 - 683
Copyright
© 2019 Cambridge University Press 

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Dighe and Gadgil supplementary movie 1

The movie presents the acoustic forcing of the liquid sheet. The natural sheet breakup mode (We 973) and acoustically forced breakup mode (We 973 120 Hz 109 dB) are shown. The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 1(Video)
Video 6.1 MB

Dighe and Gadgil supplementary movie 2

The sheet breakup sequence, We 608 120 Hz 109 dB. The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 2(Video)
Video 9.4 MB

Dighe and Gadgil supplementary movie 3

Effect of acoustic frequency on the wave pattern and sheet structure at low forcing frequency (We 973 120 Hz 109 dB). The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 3(Video)
Video 6.8 MB

Dighe and Gadgil supplementary movie 4

Effect of acoustic frequency on the wave pattern and sheet structure at high forcing frequency (We 973 440 Hz 109 dB). The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 4(Video)
Video 6.5 MB

Dighe and Gadgil supplementary movie 5

Effect of low frequency excitation on the wave amplitude (We 608, 120 Hz 109 dB). The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 5(Video)
Video 8.8 MB

Dighe and Gadgil supplementary movie 6

Effect of high frequency excitation (more than cut-off frequency based on the breakup length criterion) on the wave amplitude (We 608, 440 Hz 109 dB). Very small amplitude waves appear on the sheet and sheet is unaffected. The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 6(Video)
Video 7.1 MB

Dighe and Gadgil supplementary movie 7

Effect of acoustic forcing at very low Weber number We 10 120 Hz 109 dB. The captured frame rate is 2000 frames/sec and the display frame rate is 15 frames/sec.

Download Dighe and Gadgil supplementary movie 7(Video)
Video 7.2 MB