Finite element-based simulation of large wind turbines wake using the actuator line method

The numerical simulation of wind turbines and wind farms aerodynamics represents an open challenge in computational mechanics. It involves multi-physics and multi-scale phenomena, turbulent flows at very large Reynolds numbers, atmospheric boundary layer features, and rotor machinery flow features and dynamics. The geometrically resolved Computational Fluid Dynamics (CFD) is recognized as the highest-fidelity approach for wind turbine simulations but it has still a too high computational cost if employed for wind farm flow analysis. For this application, several reduced-order models have been formulated to obtain reliable results at a sustainable computational effort. Among the others, Large Eddy Simulations (LES) with Actuator Line Model (ALM) represents a valid middle-fidelity alternative for accurately simulating the wind turbine wakes dynamics and its interaction with the atmospheric boundary layer turbulence. Most implementations of the ALM are derived for volume-based CFD solvers. In this work we present the implementation of this model in a Finite Element Method (FEM) framework, which allows the use of a Residual Based Variational Multiscale (RBVMS) method to model the turbulent flow field, instead of the standard LES formulation. The ALM-VMS formulation is applied to study a 5MW and a 15MW wind turbine rotors, comparing the results with data available in literature in terms of aerodynamic variables of main interest, such as rotor loads and aerodynamics and near and far wake features.