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Preventing sinking of a disk by leveraging the boundary jump phenomenon

Jan Turczynowicz1,2, Radost Waszkiewicz3,1, and Łukasz Gładczuk1,*

  • *Contact author: lukasz@fenix.club
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Phys. Rev. Fluids 10, L062801 – Published 16 June, 2025

DOI: https://doi.org/10.1103/jwmb-pvyz

Abstract

Although it is commonly expected that a metal disk placed on the surface of water will sink, our investigation has revealed a surprising phenomenon: a vertical jet directed onto the disk from above can allow it to remain afloat. This result defies intuition, as one would assume that the force of the jet's impact would cause the disk to sink. We have discovered that this phenomenon occurs as a result of water displacement from the top of the disk caused by the impacting jet, operating through a mechanism similar to the hydraulic jump. This displacement increases the effective immersed volume, resulting in an increased buoyant force that balances gravity. In contrast to the classical case, here the jump radius is fixed by the geometric parameters of a disk, a phenomenon we refer to as the boundary jump. To further explore this effect, we have presented a theoretical model based on scaling laws, which provides the conditions required for the disk to float. The prefactor was determined through an independent experiment. Finally, we conducted experiments on the disk's floating and sinking, which showed a good match with the proposed theory.

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Phys. Rev. Fluids 10, L062801– Published 16 June, 2025
  • Received 1 January 2025
  • Accepted 7 May 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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