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On aerodynamic droplet breakup

Published online by Cambridge University Press:  26 February 2021

Isaac M. Jackiw
Affiliation:
Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ONM5S 3G8, Canada
Nasser Ashgriz*
Affiliation:
Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ONM5S 3G8, Canada
*
Email address for correspondence: [email protected]

Abstract

The breakup of droplets in a high-speed air stream is investigated experimentally and theoretically. This study is based on experiments conducted by exposing pendant droplets to a high-speed air jet, which allowed for imaging of the droplets at high temporal and spatial resolutions while maintaining a large field of view to capture the breakup process. Two factors of primary importance in droplet breakup are the breakup morphology and the resulting child droplet sizes. However, benchmark models have erroneous assumptions that impede the prediction of both morphology and breakup size and give non-physical geometries. The present theoretical work focuses on the ‘internal flow’ hypothesis, which suggests that the droplet's internal flow governs its breakup. The breakup process is subdivided into four stages: droplet deformation, rim formation, rim expansion and rim breakup. The internal flow mechanism is used to mathematically model the first two stages. The rim expansion is related to the growth of bags, while its breakup is shown to be due to Rayleigh–Plateau capillary instability. It is found that the breakup morphology is related to the division of the droplet into a disk that forms on the windward face and the undeformed droplet core. The amount of the droplet volume contained in the undeformed core decides the breakup morphology. Using this framework, it is shown that a three-step calculation can give an improved prediction of child drop sizes and morphology.

Type
JFM Papers
Copyright
© The Author(s), 2021. Published by Cambridge University Press

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Jackiw and Ashgriz supplementary movie 1

Side-view of Bag breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 1(Video)
Video 1.1 MB

Jackiw and Ashgriz supplementary movie 2

End-on view of Bag breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 2(Video)
Video 895.4 KB

Jackiw and Ashgriz supplementary movie 3

Side-view of Bag & Stamen breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 3(Video)
Video 810.2 KB

Jackiw and Ashgriz supplementary movie 4

End-on view of Bag & Stamen breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 4(Video)
Video 1.1 MB

Jackiw and Ashgriz supplementary movie 5

Side-view of Multibag breakup morphology where core breaks as single bag. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 5(Video)
Video 755.6 KB

Jackiw and Ashgriz supplementary movie 6

End-on view of Multibag breakup morphology where core breaks as single bag. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 6(Video)
Video 913 KB

Jackiw and Ashgriz supplementary movie 7

Side-view of Multibag breakup morphology where core breaks as multiple bags. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 7(Video)
Video 665.3 KB

Jackiw and Ashgriz supplementary movie 8

End-on view of Multibag breakup morphology where core breaks as multiple bags. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 8(Video)
Video 1 MB

Jackiw and Ashgriz supplementary movie 9

Side-view of Sheet-Thinning breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 9(Video)
Video 371.7 KB

Jackiw and Ashgriz supplementary movie 10

End-on view of Sheet-Thinning breakup morphology. Experiment conditions are annotated with the elapsed non-dimensional time. In parentheses is the dimensional time in ms. Playback speed is 15 FPS.

Download Jackiw and Ashgriz supplementary movie 10(Video)
Video 931.4 KB
Supplementary material: File

Jackiw and Ashgriz supplementary material

Supplementary data
Download Jackiw and Ashgriz supplementary material(File)
File 40.2 KB