Wave breaking and jet formation on axisymmetric surface gravity waves

M.l. Mcallister, S. Draycott, T. Davey, Y. Yang, T.a.a. Adcock, S. Liao, T.s. Van Den Bremer

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Abstract

Axisymmetric standing waves occur across a wide range of free surface flows. When these
waves reach a critical height (steepness), wave breaking and jet formation occurs. For
travelling surface gravity waves, the process of wave breaking is generally considered to
limit wave height and reversible wave motion. In the ocean, the behaviour of directionally
spread waves lies between the limits of purely travelling (2D) and axisymmetric (3D).
Hence, understanding wave breaking and jet formation on axisymmetric surface gravity
waves is an important step in understanding extreme and breaking waves in the ocean.
We examine an example of axisymmetric wave breaking and jet formation colloquially
known as the ‘spike wave’, created in the FloWave circular wave tank at the University of
Edinburgh, UK. We generate this spike wave with maximum crest amplitudes of 0.15-6.0
m (0.024-0.98 when made non-dimensional by characteristic radius), with wave breaking
occurring for crest amplitudes greater than 1.0 m (0.16 non-dimensionalised). Unlike
2D travelling waves, wave breaking does not limit maximum crest amplitude, and our
measurements approximately follow the jet height scaling proposed by Ghabache et al.
(2014) for cavity collapse. The spike wave is predominantly created by linear dispersive
focusing, which forms a deep wave trough. This trough or cavity then collapses producing
a jet, which is highly sensitive to the trough’s shape. The evolution of the jets that form
in our experiments is predicted well by the hyperbolic jet model proposed by LonguetHiggins
Original languageEnglish
JournalJournal of Fluid Mechanics
Volume935
Early online date25 Jan 2022
DOIs
Publication statusPublished - 25 Mar 2022

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