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Droplet size distribution in a swirl airstream using in-line holography technique

Published online by Cambridge University Press:  06 January 2023

Someshwar Sanjay Ade
Center for Interdisciplinary Program, Indian Institute of Technology Hyderabad, Kandi, Sangareddy 502 284, Telangana, India
Pavan Kumar Kirar
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy 502 284, Telangana, India
Lakshmana Dora Chandrala*
Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy 502 284, Telangana, India
Kirti Chandra Sahu*
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy 502 284, Telangana, India
Email addresses for correspondence:,
Email addresses for correspondence:,


We investigate the morphology and size distribution of satellite droplets resulting from the interaction of a freely falling water droplet with a swirling airstream of different strengths by employing shadowgraphy and deep-learning-based digital in-line holography techniques. We found that the droplet exhibits vibrational, retracting bag and normal breakup phenomena for the no swirl, low and high swirl strengths for the same aerodynamic field. In the high-swirl scenario, the disintegrations of the nodes, rim and bag-film contribute to the number mean diameter, resulting in smaller satellite droplets. In contrast, in the low-swirl case, the breakup of the rim and nodes only contributes to the size distribution, resulting in larger droplets. The temporal variation of the Sauter mean diameter reveals that for a given aerodynamic force, a high swirl strength produces more surface area and surface energy than a low swirl strength. The theoretical prediction of the number-mean probability density of tiny satellite droplets under swirl conditions agrees with experimental data. However, for the low swirl, the predictions differ from the experimental results, particularly due to the presence of large satellite droplets. Our results reveal that the volume-weighted droplet size distribution exhibits two (bi-modal) and three (multi-model) peaks for low and high swirl strengths, respectively. The analytical model that takes into account various mechanisms, such as the nodes, rim and bag breakups, accurately predicts the shape and characteristic sizes of each mode for the case of high swirl strength.

JFM Papers
© The Author(s), 2023. Published by Cambridge University Press

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Ade et al. Supplementary Movie 1

The animation depicts different holography reconstructed planes at different depths. This corresponds to figure 3.

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Video 4.9 MB

Ade et al. Supplementary Movie 2

The vibrational breakup mode in Figure 5 (Sw = 0).

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Video 10.4 MB

Ade et al. Supplementary Movie 3

The retracting bag breakup mode in Figure 5 (Sw = 0:47).

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Video 8 MB

Ade et al. Supplementary Movie 4

The bag breakup mode in Figure 5 (Sw = 0:82).

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Video 7.8 MB
Supplementary material: PDF

Ade et al. Supplementary Material

Ade et al. Supplementary Material

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