La turbulencia asociada con velocidades orbitales de olas que aún no rompen

Abstract

Ocean-atmosphere exchange processes are known to decisively determine the sea state, the weather and our planet´s climate. With the ultimate goal of a better understanding of the processes contributing with turbulent kinetic energy into both boundary layers above and below the sea surface, we approach the ocean surface wave phenomenon, and in particular we study the non-breaking waves potential effect. Therefore, measurement of particle velocities were made in a fluid under non-breaking waves, for the purpose of detecting turbulence and its association with the wave steepness. A total of 184 experiments were analyzed, each one with a duration of 3.5 minutes and the presence of approximately monochromatic waves with varying steepness (0.012-0.273). The measurements were carried out in a wave tank with dimensions of 12.26 m × 0.55 m x 0.32 m using an acoustic velocimeter (Vectrino Profiler, Nortek). The u, v and w components of velocity were measured on a 3.5 cm long fluid column in 35 cells of 1 mm in height. During the experiments, the voleocity profile between 1.5 cm and 8.6 cm depth was obtained, referred to the water level in the wave tank (h = 48.6 cm ± 0.5 cm). The waves propagated in deep waters (h/λ > 0.5), where λ is the wave length. Only u(t, z) and w(t, z) components were considered for the analysis since, waves are practical two-dimensional (v(t, z) = 0). Power spectra were calculated in as function of frequency corresponding to u'(t, z) and w'(t, z) turbulent fluctuations, an inertial subrange (isotropic turbulence) was detected in the most of the spectra, for certain depths regardless of the wave steepness. Results from turbulent fluctuations frequency spectra show that eddy size involved in transferring energy to smaller ones, increases with the wave slope.