The perturbation method - A novel large-eddy simulation technique to model realistic turbulence: Application to tidal flow

Abstract

Abstract Turbulence in the ocean dominates the vertical movement of heat and salt, as well as chemical and biological particulates. The modelling of turbulence is therefore essential to forecast the strength of the biological pump, for example, in which CO2 is drawn out of the atmosphere and trapped in the deep ocean. Obtaining observations of turbulence is an expensive process and the modelling of turbulence still remains an open problem. Using state-of-the-art 3D hydrodynamic models, such as Large-Eddy Simulation and Direct Numerical Simulation, to understand turbulence driven by mean flow is a popular method. However in this approach, the turbulence creates its own mean flow contribution which, in some applications, results in an undesirable divergence from the prescribed mean flow. Here, the perturbation method is introduced. This technique ensures zero divergence to the prescribed mean flow. Results reveal the high level of accuracy this approach has in replicating the observed turbulent field when using ADCP mean current data to prescribe the model mean flow. It is envisaged that the user-friendly nature of this method will enable non-specialists to derive turbulence data when turbulence profilers are not a tractable resource. This modelling approach also sets a rigid framework for the testing of turbulence closure schemes.