The coupling between idealized 2D eddies and 3D small-scale turbulence in the upper ocean and its implications for oil transport simulations using ENDLESS

As oil plumes from deep-water blowouts reach the ocean mixed layer (OML), they experience considerable horizontal and vertical dilution due to the action of Langmuir turbulence, submesoscale eddies and Ekman transport. Previous studies using large-eddy simulation (LES) have shown that Langmuir turbulence can impact the transport direction, lateral diffusion and geometry of surface oil plume, depending on the size of oil droplets. However, the large range of relevant length scales, from submesoscale eddies down to small-scale 3D Langmuir turbulence, makes it challenging to accurately reproduce the long-term evolution of oil plumes in the upper ocean using conventional large-eddy simulation strategies. The extended nonperiodic domain large-eddy simulation for scalars (ENDLESS) is a new technique developed as a multi-scale approach to simulate long-term oil plume dispersion at a reasonable computational cost. The basic idea is to simulate Langmuir turbulence on a LES domain with a small but sufficient horizontal domain size to capture the essential physics of the flow field, while simulating the oil plume evolution over an effectively horizontally extended large domain. Moreover, this ENDLESS method permits the superposition of large-scale quasi-2D ocean eddies on the oil advection, allowing for coupling with regional ocean circulation models. Using this new numerical tool, the effects of the interactions between 3D turbulence and 2D eddies on the flow field and on oil dispersion are elucidated by comparing the results from ENDLESS with those from conventional LES. This research was made possible by a grant from The Gulf of Mexico Research Initiative.