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An experimental investigation of droplet morphology in swirl flow

Published online by Cambridge University Press:  09 March 2022

Pavan Kumar Kirar
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India
Surendra Kumar Soni
Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India
Pankaj S. Kolhe*
Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India
Kirti Chandra Sahu*
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502 284, Telangana, India
Email addresses for correspondence:,
Email addresses for correspondence:,


The interaction of a droplet with a swirling airstream is investigated experimentally using shadowgraphy and particle image velocimetry techniques. In swirl flow, the droplet experiences oppose-flow, cross-flow and co-flow conditions depending on its ejection location, the velocity of the airstream and the swirl strength, which results in distinct droplet morphologies as compared with the straight airflow situation. We observe a new breakup phenomenon, termed as ‘retracting bag breakup’, as the droplet encounters a differential flow field created by the wake of the swirler's vanes and the central recirculation zone in swirl airflow. A regime map demarcating the various modes, such as no breakup, vibrational breakup, retracting bag breakup and bag breakup modes, is presented for different sets of dimensionless parameters influencing the droplet morphology and its trajectory. In contrast to the straight flow, the swirl flow promotes the development of the Rayleigh–Taylor instability, enhancing the stretching factor in the droplet deformation process, resulting in a larger number of fingers on the droplet's surface. In order to gain physical insight, a modified theoretical analysis based on the Rayleigh–Taylor instability is proposed for the swirl flow. The experimental behaviour of droplet deformation phenomena in swirl flow conditions can be determined by modifying the stretching factor in the theoretical model.

JFM Papers
© The Author(s), 2022. Published by Cambridge University Press

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Kirar et al. supplementary movie 1

An animation showing the vibrational (first row), retracting bag breakup (second row) and bag breakup (third row). This movie corresponds to figure 2 of the main manuscript.

Download Kirar et al. supplementary movie 1(Video)
Video 21.9 MB

Kirar et al. supplementary movie 2

An animation showing the front and top views of a retracting bag breakup morphology. This movie corresponds to figure 3 of the main manuscript.

Download Kirar et al. supplementary movie 2(Video)
Video 24 MB