Langmuir turbulence is a boundary layer oceanographic phenomenon of the upper layer that is relevant to mixing and vertical transport capacity. It is a manifestation of imposed aerodynamic stresses and the aggregate horizontal velocity profile due to orbital wave motion (the so-called Stokes profile), resulting in streamwise-elongated, counterrotating cells. The majority of previous research on Langmuir turbulence has focused on the open ocean. Here, we investigate the characteristics of coastal Langmuir turbulence by solving the grid-filtered Craik–Leibovich equations where the distinction between open and coastal conditions is a product of additional bottom boundary layer shear. Studies are elucidated by visualizing Langmuir cell vortices using isosurfaces of Q. We show that different environmental forcing conditions control the length scales of coastal Langmuir cells. We have identified regimes where increasing the Stokes drift velocity and decreasing surface wind stress both act to change the horizontal size of coastal Langmuir cells. Furthermore, wavenumber is also responsible in setting the horizontal extent Ls of Langmuir cells. Along with that, wavenumber that is linked to the Stokes depth δs controls the vertical extent of small-scale vortices embedded within the upwelling limb, while the downwelling limb occupies the depth of the water column H for any coastal surface wave forcing (i.e., and ). Additional simulations are included to demonstrate insensitivity to the grid resolution and aspect ratio.

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Experimental results for instabilities present in a rotating Hagen-Poiseuille flow are reported in this study through fluid flow visualization. First, we found a very good agreement between the experimental and the theoretical predictions for the onset of convective hydrodynamic instabilities. Our analysis in a space-time domain is able to obtain quantitative data, so the wavelengths and the frequencies are also estimated. The comparison of the predicted theoretical frequencies with the experimental ones shows the suitability of the parallel, spatial and linear stability analysis, even though the problem is spatially developing. Special attention is focused on the transition from convective to absolute instabilities, where we observe that the entire pipe presents wavy patterns, and the experimental frequencies collapse with the theoretical results for the absolute frequencies. Thus, we provide experimental evidence of absolute instabilities in a pipe flow, confirming that the rotating pipe flow may be absolutely unstable for moderate values of Reynolds numbers and low values of the swirl parameter.