ENDLESS: a multi-scale large-eddy simulation approach to study oil plumes in the ocean mixed layer

Large-eddy simulation (LES) has proven to be a valuable tool in producing high-fidelity simulations of environmental and geophysical turbulent flows. For simulations of the ocean mixed layer (OML), a grid size of a few meters is required and the typical horizontal domain sizes of LES are restricted to hundreds meters or a few kilometers at most. Oil plumes being transported in the OML experience the action of Langmuir turbulence, Ekman transport and submesoscale quasi-geostrophic eddies. As a consequence, oil plumes display complex features on scales from a few meters to tens kilometers. Therefore, accurately reproducing all the relevant scales in computer simulations is a challenging task. In this study, the Extended Nonperiodic Domain LES for Scalar transport (ENDLESS) is proposed as an economic multi-scale approach to tackle this problem with current computing power. The basic idea is to simulate the Langmuir turbulence on a small horizontal domain while simulating the oil plume over an effectively large extended domain. In particular, scalar fields are adaptively added and removed to efficiently enclose the oil plume with minimum computational cost for tracking the evolution of nonhomogeneous plumes. This approach also permits the superposition of larger-scale quasi two-dimensional motions on the oil advection, allowing for coupling with regional circulation models. Validation cases and sample applications are also discussed.