Turbulence characterization at a tidal energy site using large-eddy simulations: case of the Alderney Race

Abstract

Sites suitable for the deployment of tidal turbines generally show a combination of complex seabed morphologies and extreme current magnitudes. Such configurations favour the formation of vortices, which can be very powerful. Anticipating the vortex effect on the turbine performance and/or lifespan requires refined description of the turbulence. Thanks to increased calculation resources, large-eddy simulation (LES) can now be applied to natural flow. An LES approach developed within the TELEMAC-3D open-source software is presented here. After validating the model with in-situ measurements, the model is applied to characterize the flow statistics of the Alderney Race. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race’.

Numerical modelling of hydrodynamics and tidal energy extraction in the Alderney Race: a review

“…[34] and Bourgoin et al . [31] agreed well with the turbulence measurements acquired in the AR. Their work using LES also paved the way to a better understanding of the dynamics of the largest eddies that may impact the tidal turbines deployed in the AR.…”

“…The LES approach is thus a good candidate for characterizing the ambient turbulence of tidal stream energy sites. In the AR, LES has been performed with a modified version of Telemac3D [30,31] with the objective of identifying the morphological features of the seabed that trigger the formation of the largest eddies. Before applying the model to the AR, numerous developments were carried out to transform the RANS Telemac solver into an LES model.…”

“…Those developments included, among others, improvements to the convection–diffusion scheme (to reduce spurious numerical dissipation), the inclusion of a synthetic eddy method (to generate incoming eddies at the boundary of the LES domain) and the implementation of subgrid-scale turbulence models. After different validation steps [32], Bourgoin [30,31] simulated the hydrodynamics of the AR with a Telemac3D model, which captured the tidal dynamics over a 100 km × 100 km zone with a RANS approach and switched to the LES formulation in a 3 km × 3 km zone located in the AR, with a minimum cell size of 5 m. Although their predictions of turbulent intensity were still underestimated (especially in the upper part of the water column), the use of LES resulted in more reliable turbulence estimates than the RANS approach. Mercier et al .…”

“…[33,34] also used LES to characterize the turbulence of the AR. Complementing [30,31], they focused on a smaller domain and used a much finer spatial resolution (minimum cell size of 0.25 m). Their simulation relied on the lattice Bolztmann method (LBM), which has the advantages of minimizing the numerical dissipation and enabling efficient parallelization (which is important due to the significant computational cost associated with LES modelling).…”

“…The model of Bourgoin et al . [31], which used a coarser mesh but covered a larger domain and a longer period of time, required comparable computational resource (of the order of 100 000 h.CPU). This limitation of LES prevents from approaching larger domains and longer time-scales (neap/spring tides, flood/ebb tides, different meteorological/wave conditions).…”