Towards the use of large eddy simulations of the atmospheric boundary layer for wind turbine aeroelastic load calculations

This joint TNO-Whiffle report presents the main results obtained in the third work package of the AeroLES project. The project aims to reduce the uncertainty in the design chain of modern wind turbines by replacing traditional synthetic inflow generation methods with validated wind fields from high-fidelity large eddy simulations (LES) that better resemble reality. Potentially, this would reduce the gap between in-field and simulated inflow conditions enabling better design choices that reduce the cost of the assets. To reach such an ambitious goal, however, several intermediate steps need to be undertaken. The present work starts by highlighting the main challenges associated with the use of LES for generating the inflow for wind turbine aeroelastic load calculations. The inflow validation challenge is then tackled in Chapter 2, where LES wind field statistics are validated against met mast measurements at two onshore and one offshore sites. The comparison shows a promising agreement overall, with onshore turbulence intensity being subject to higher uncertainty than off shore due to its sensitivity to the surface roughness parameter. Then, to tackle the computational cost challenge and enable efficient LES-based aeroelastic calculations, a software interface that couples Whiffle’s LES solver running on Graphical Processing Units (GPU) to a multi-physics simulation tool has been developed (Chapter 3). The tool allows running simulations both in a one-way coupled approach, where the turbine is not modelled in the LES and conventional wake models are used to compute aerodynamic loads, and in a two-way coupled actuator line approach where the turbine wake is modelled in the LES for higher fidelity. Finally, looking for suitable simulation settings and guidelines for using LES in aeroelastic load calculations, a grid sensitivity study is presented in Chapter 4. The power spectral densities of relevant aeroelastic quantities are found to be sensitive to the mesh resolution, not only in the high-frequency part of the spectrum where an energy drop occurs due to spatial filtering, but also at lower nP harmonics where coarse grids appear not entirely able to capture the peaks resulting from the rotational sampling of the turbulence