Bathymetry induced turbulence modelling the Alderney Race site : regional approach with TELEMAC-LES

Abstract : Nowadays tidal currents are considered a promising renewable energy source. Many worldwide projects involve the installation of different types of marine current energy converters. The characterisation of marine resources is therefore essential to increase efficiency of energy production. Areas with high hydroturbine potential are particularly subject to multi-scale turbulence, ranging from small vortices able to cause large fatigue loads, to large vortices capable of disrupting turbine production. A better knowledge of the generation of these eddies and their propagation is essential. This is the purpose of the ANR/FEM THYMOTE project (Turbulence, Hydrolienne, Modélisation, Observations et TEsts en bassin) studying one of the most promising sites in Europe: the Alderney Race. One of the questions raised concerns the ability of large morphological structures on the seabed to produce eddies. The adopted method uses a 3D regional model to cover the area occupied by these bedforms.Regional models such as TELEMAC-3D use a turbulent URANS (Unsteady Reynolds Averaged Navier Stokes) closure, with for example the $k-\varepsilon$. This approach does not allow a detailed description of the instability of turbulence. However, thanks to the increase in computing resources, the large scale method (LES) becomes feasible. This is based on flow filtering, and consists of simulating only the largest turbulence scales, whereas the smaller ones are modeled. The TELEMAC-3D code was modified during this thesis in order to introduce this turbulent closure. The code developed allows free surface flows to be simulated over a wide range of scales from turbulence to tidal propagation. The TELEMAC-LES code has been validated on the basis of experimental results from the literature. It is then used to study turbulent flows in the Alderney Race using a nesting strategy. The LES method allows a detailed description of the turbulence of these environments. It finally leads to the identification of energetic vortex structures, and thus the definition the most appropriate zones for the installation of tidal turbines.
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Adrien Bourgoin. Bathymetry induced turbulence modelling the Alderney Race site : regional approach with TELEMAC-LES. Fluids mechanics [physics.class-ph]. Normandie Université, 2019. English. ⟨NNT : 2019NORMC205⟩. ⟨tel-02310681v2⟩

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