Large-Eddy Simulations and Direct Numerical Simulations of the Turbulent Ocean

Dear Colleagues,

Over the past two decades, large-eddy simulations (LES) have gained popularity in applications related to turbulence in the ocean. A large number of LES of oceanic (surface and bottom) boundary layers have been performed with the goal of obtaining an improved understanding of the role of wind, waves, and tidally-driven turbulence in the vertical mixing and transport of momentum and scalars. Recently, attention has been paid to the use of LES to determine the role of turbulence in the transport of hazardous materials, such as spilled oil. Another important use of LES has been to provide databases for the development and/or calibration of turbulence parameterizations suitable for coarse scale solvers of the larger scale oceanic general circulations, based on the Reynolds-averaged Navier–Stokes (RANS) equations. Meanwhile, advances in interface tracking and interface capturing numerical techniques have led to the direct numerical simulation (DNS) of scales in the order of centimeters, with resolutions of molecular sublayers on the air and water sides, in order to gain understanding of gas transfer and temperature variations across the air–water interface. DNS and LES have also been applied to laboratory-scale geophysical flows in order to elucidate, for example, the turbulence structure and interactions with other competing mechanisms, such as stable stratification and associated internal waves, as well as interactions with rotation and bottom topography. More recently, as computational resources have become more accessible, LES has been applied to resolve oceanic sub-mesoscale eddies with a horizontal length scale of tens of kilometers and their important interactions with smaller scale turbulence, in particular as they relate to surface dispersion and near-surface vertical mixing. Traditionally, LES and DNS of turbulence in the ocean have been performed with high order discretization schemes, such as pseudo spectral methods. However, with the development of advanced fluid-structure interaction solvers at the scales of LES, and their increased applications to wind, wave and tidal energy-related flows, there is new demand for the accurate representation of oceanic boundary layer turbulence by these solvers, which are often of relative low order accuracy. Meanwhile, as LES and DNS have gained popularity for oceanic flows, new developments in turbulence modelling for traditional simulation approaches based on the RANS equations have continued. For example, improved first and second order turbulence closures accounting for Langmuir turbulence in the upper ocean have recently been developed and tested. This Special Issue will serve as a compendium of the most recent applications of LES, DNS and RANS simulation to ocean flows, highlighting the underlying turbulent processes, the necessary numerical discretizations and the subgrid-scale and turbulence modelling techniques.

Prof. Dr. Andres E. Tejada-Martinez
Guest Editor

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• LES
• RANS
• DNS
• Turbulence closures
• Oceanic boundary layers
• Wave and tidal energy