Observation of turbulence and intermittency in wave-induced oscillatory flows
Alberello, A.; Onorato, M.; Frascoli, F.; Toffoli, A. (2019). Observation of turbulence and intermittency in wave-induced oscillatory flows. Wave Motion 84: 81-89. https://dx.doi.org/10.1016/j.wavemoti.2018.10.003
In: Wave motion. North-Holland: Amsterdam. ISSN 0165-2125; e-ISSN 1878-433X, meer
The dynamic and thermal regimes of the climate are regulated by an exchange of energy and momentum between the atmosphere and the ocean. The role exerted by surface waves on this interchange is particularly enigmatic. Waves induce turbulence in the upper ocean by breaking and through Langmuir circulations. However, there is evidence that the wave oscillatory flow can be turbulent and directly inject mixing into subsurface layers. The existence, extent and properties of this non-breaking, wave-induced turbulent flow still remain uncertain. Here we present measurements of the velocity field of oscillatory flows, which are induced by mechanically generated random wave fields in a large scale experimental facility. Velocities were recorded at a depth sufficiently far from the water surface to rule out the effects of wave breaking. We demonstrate that the spectral tail of the velocity field follows a power-law scaling close to omega(-5/3), with omega being the radial frequency. The turbulent behaviour is investigated via rigorous statistical analysis of the structure functions to highlight the emergence of intermittency in oscillatory flows.
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