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Onset of vortex shedding behind a circular cylinder in a flowing soap film

Published online by Cambridge University Press:  18 December 2025

Izhar Hussain Khan Open the ORCID record for Izhar Hussain Khan [Opens in a new window]  and
Sanjay Kumar Open the ORCID record for Sanjay Kumar [Opens in a new window]
Izhar Hussain Khan
Affiliation:
Department of Aerospace Engineering, Indian Institute of Technology Kanpur , Kanpur, Uttar Pradesh 208016, India
Sanjay Kumar*
Affiliation:
Department of Aerospace Engineering, Indian Institute of Technology Kanpur , Kanpur, Uttar Pradesh 208016, India
*
Corresponding author: Sanjay Kumar, skmr@iitk.ac.in
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Abstract

In this experimental study, we investigate, for the first time, the structure and evolution of the near wake of a circular cylinder in a flowing soap film at the onset of vortex shedding. The study primarily focuses on the changes occurring within the recirculation bubble, along with the evolution of vortex shedding. A significantly large recirculation bubble forms behind the cylinder in the soap film environment, characterized by small-scale vortices along its edges, an observation that starkly contrasts with its three-dimensional counterparts. These small-scale vortices driven by the Kelvin–Helmholtz instability, further induce a transverse deflection of the recirculation bubble, leading to an intermittent generation of the wake vortices. The instantaneous velocity field in the wake is examined, highlighting the clear evidence of intermittency in vortex formation. The frequency and wavelength of the chain of small-scale vortices on the recirculation bubble is evaluated, and a functional relationship with the flow Reynolds number is determined. We believe this observation to be novel, potentially revealing a new pathway for understanding the two-dimensional transition in bluff-body wakes.

JFM classification

Vortex Flows: Vortex shedding Wakes/Jets: Vortex streets

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Type
JFM Papers
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Journal of Fluid Mechanics , Volume 1025 , 25 December 2025 , A39
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Copyright
© The Author(s), 2025. Published by Cambridge University Press

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