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Wind energy extraction is among the most mature solutions for renewable energy. To increase its annual energy production and penetration, the size of the turbines has been increasing remarkably during the years. This tendency involves more flexible blades and thus a stronger Fluid-Structure Interaction (FSI). Hence, it is fundamental to correctly model and simulate turbines numerically, to minimize costly experimental campaigns and to have a deeper physical insight. Modern aeroelastic codes primarily use blade element momentum theory or inviscid methods for the fluid part and finite element, modal or multibody method for the structural part. For example, in unsteady mode, the widely used code FAST1 combines a potential flow model with a multibody formulation. In this work we present a novel two-way coupling method exploiting the accuracy of Large Eddy Simulation (LES) for the fluid description and the efficiency of the modal method for the structural description. The model leverages the formulation of the Actuator Line Model2 (ALM) in our incompressible LES solver3. In the ALM, the blades are represented in the fluid equations as body forces distributed along lines corresponding to each rotor blade. The code evaluates the forces by using tabulated airfoil data and the local incidence obtained from the sampling of the local flow field. To establish an aeroelastic feedback, we added to the relative flow field the deformation velocity from structural dynamics, which is forced at every instant by the loads known at the previous time step. Several studies suggest that the blades are the most relevant components of the turbine for FSI, thus we used a beam model to consider only their structural response. Given the need for an efficient structural solver, to be coupled with computationally heavy LESs, we opted for a modal description. To consider inertial coupling in modal basis, we used the approach in Saltari et al.4. We are performing coupled simulations of the NREL 5 MW benchmark turbine5 in turbulent conditions to validate our model. We will analyse the effects of the dynamic deformation on the wake and on fatigue loads by comparing our results with those of uncoupled LESs and of state-of-the-art aeroelastic codes. 1 Jonkman et al., NREL, NREL/EL-500-38230, (2005) 2 Sorensen and Shen, J. Fluids Eng., 124.2, 393 (2002) 3 Santoni at al., Wind Energy, (2020) 4 Saltari et al., J. Aircr., 54(6), 2350 (2017) 5 Jonkman et al., NREL, NREL/TP-500-38060, (2009) |
