D2.2 - Report on AL enhancement and turbulence model

Description of task 2.3: LES-Park will be developed in OpenFoam. The wind flow in the wind park will be estimated using large eddy simulation technique (LES) technique, while the influence of the blades on the flow field will be approximated by the Actuator Line Model (ALM). Existing ALM will be improved to account for the nacelle and tower effects. A filter-based model will be designed to overcome shortcoming associated with existing turbulence model. In filter-based model, transport equations for sub filter energy and sub filter dissipation rate will be modelled and for turbulent eddy viscosity exponential relaxation function will be solved. The dissipation model based on macroscopic turbulent length scale will be implemented. The model equations will be solved in OpenFoam architecture. UPWARDS LES-Park model will be based on improved ALM and filter-based turbulence model. The LES-Park will be verified against field data for Offshore wind Park (i.e. Lillgrund).

A full CFD method (resolving wind turbines on the grid scales), methods are computationally demanding and almost impossible to apply in the design and optimization of wind farms and park control. To overcome these challenges, a method based on combing CFD and BEM has been developed [1–4]. In this coupled method, the wind turbines are not resolved on the grid, but the effect of turbines on the flow field is modelled and this effect is modelled either using the actuator disk method (ADM) or actuator line method (ALM). However, both ALM and ADM are unable to resolve the detailed geometrical features of turbine blades on a mesh. To alleviate this problem an improved ALM approach, Actuator Surface Models (ASM) for turbine blades, which take into account more geometrical details have been studied. In the present study, the ASM approach has been implemented in OpenFom. The effect of tower and nacelle is also included in the wind farm simulations. The loads on each surface of the turbine are estimated using the Blade Element Method (BEM). The model is validated with available literature data and preliminary results are presented here. Filter-based turbulence model developed by SINTEF have been implemented and tested. The work have been already presented at Deepwind conference at Trondheim Norway.