Large Eddy Simulations of Wind Turbines

Over the past years the demand of energy from renewable sources has been increasing due to increased environmental awareness and foreseeable shortage of non-renewable energies. This has had a strong impact on wind energy powerplants. In fact in order to supply large quantities of energy high-density clusters of wind turbines have been designed. However, the actual production has been lower than the expected because of wake interactions, which are more severe as more densely the turbines are placed, and turbulent motion. It follows that in order to optimize the power extraction from wind a deep understanding of wakes features and dynamics is required. Historically employed engineering models do not provide such a detailed knowledge and their predictions on wakes characteristics may be quite erroneous due the simplifying assumptions they rely upon. Conversely Large-Eddy Simulations (LES) take into account the dynamics of wind turbine flows without making a priori hypotheses on airflow behaviour. Therfore LES results are expected to be more detailed and accurate. In the present thesis, LES of wind turbine flows have been performed. The results obtained have been discussed and compared to the predictions of the simplified engineering models. The impact of the subgrid-scale (SGS) model, which is a key feature of LES, has also been investigated within the framework of eddy-viscosity subgrid-scale models