Skipping under water: Buoyant sphere hydrodynamics at the air–water interface

Farrukh Kamoliddinov, Ivan Uriev Vakarelski, Sigurdur T Thoroddsen, T. T. Truscott

Research output: Contribution to journalArticlepeer-review


We present an experimental study of the hydrodynamics of a buoyant sphere accelerated horizontally along an air–water interface. At low speeds, the sphere floats at the surface, while at higher speeds, the sphere starts oscillating, moving below and toward the free surface akin to underwater skipping. The sphere often breaches and forms an air cavity during its subsequent dive. These underwater air cavities become horizontal and are attached to the sphere surface near the laminar flow separation point (∼π/2). High-speed imaging is used to investigate the effects of changing the pulling angle and counterweight-induced velocity on the hydrodynamics. We examine the transition from underwater skipping oscillations to water exit, particularly above the critical Froude number of 1.2, where buoyant spheres experience complex fluid–solid interactions revealing the influence of the air cavity on drag and lift coefficients and overall sphere hydrodynamics. Finally, we analyze the novel phenomenon of the steady motion of the horizontally pulled sphere with an attached inverted-wing-shaped air cavity.
Original languageEnglish (US)
JournalPhysics of Fluids
Issue number7
StatePublished - Jul 11 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-07-14
Acknowledged KAUST grant number(s): URF/1/3723-01-01
Acknowledgements: The work was supported by the King Abdullah University of Science and Technology (KAUST) under Grant No. URF/1/3723-01-01. IUV acknowledges the support from the Operational Programme “Science and Education for Smart Growth,” Bulgaria, Project No. BG05M2OP001-1.002-0023.

ASJC Scopus subject areas

  • Condensed Matter Physics


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