Variational multiscale modeling of Langmuir turbulent boundary layers in shallow water using Isogeometric Analysis

We present large-eddy simulations (LES) of wind and wave-driven turbulent boundary layers in shallow water with Langmuir circulation using a variational multi-scale formulation of the Craik-Leibovich equations. The simulations are performed using Isogeometric Analysis (IGA) based on quadratic non-uniform rational basis spline (NURBS) basis functions. Wind and wave-driven turbulent boundary layers over a flat bottom surface representative of open ocean conditions in inner-shelf regions with turbulent Langmuir number La-t = 0.7 and wind stress friction Reynolds number Re-tau = 395 are first simulated. The present results agree well with the reference results based on a spectral LES with higher mesh resolution [1]. Then, to investigate the effect of seabed topography on the turbulence, we simulate turbulent boundary layers over a sloped bottom surface with wind and wave forcing parallel to the shore, representative of a surf-shelf transition zone. We find that the Langmuir cell size increases as the water column shallows approaching onshore and the cell center shifts to the onshore direction. The mean velocity and turbulent kinetic energy along the shore are quantified. (C) 2020 Elsevier Ltd. All rights reserved.