Abstract. The aeroelastic response of a 2 MW NM80 turbine with a rotor diameter of 80 m and interaction phenomena are investigated by the use of a high-fidelity model. A time-accurate unsteady fluid–structure interaction (FSI) coupling is used between a computational fluid dynamics (CFD) code for the aerodynamic response and a multi-body simulation (MBS) code for the structural response. Different CFD models of the same turbine with increasing complexity and technical details are coupled to the same MBS model in order to identify the impact of the different modeling approaches. The influence of the blade and tower flexibility and of the inflow turbulence is analyzed starting from a specific case of the DANAERO experiment, where a comparison with experimental data is given. A wider range of uniform inflow velocities are investigated by the use of a blade element momentum (BEM) aerodynamic model. Lastly a fatigue analysis is performed from load signals in order to identify the most damaging load cycles and the fatigue ratio between the different models, showing that a highly turbulent inflow has a larger impact than flexibility, when low inflow velocities are considered. The results without the injection of turbulence are also discussed and compared to the ones provided by the BEM code AeroDyn.

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This work is intended to investigate the aerodynamic responses of a large generic 10-MW offshore wind turbine under turbulent inflow conditions. The nonlinear lifting line free vortex wake simulations approach is employed for this purpose, computed using the QBlade code. In these studies, the effects of a three-dimensional correction model for the airfoil polars were studied in advance. For this purpose, the blade element momentum computations employing the corrected polars are performed and compared to computational fluid dynamics simulations, and a good agreement is obtained between both employed approaches. Background turbulence is then imposed in the QLLT simulations with the turbulence intensities ranging from low to high turbulence levels (3%-15%). Furthermore, the impact of wind shear from different locations (offshore and onshore) is investigated in this work.

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Abstract. This paper shows the results of CFD studies of turbulent flow fields and their effects on a wind turbine in complex terrain. As part of the WINSENT project a research test site comprising four meteorological masts and two research wind turbines is currently being constructed in the Swabian Alps in Southern Germany. This work is an essential part of the research of the Southern German wind energy research cluster WindForS. The terrain site is characterised by a densely forested escarpment and a flat plateau downstream of the slope. The met masts and wind turbines are built on this plateau. In the first part, high-resolution CFD simulations are performed to separately investigate the effects of the forested escarpment and of thermal stratification on the flow field and on the wind turbine accordingly. In the second part, all the examined effects are combined for a real-life case dated March 2021. There, unstable conditions prevailed and the forest shows low leaf area densities due to the wintertime. It is shown that atmospheric turbulence, forests, orographies, and thermal stratification must be considered when assessing the impact of wind turbines in complex terrain. All of these effects influence the flow field both at the turbine position as well as in its wake. Turbulent structures of the forest wake cross the rotor plane temporarily and thereby affect the turbine inflow. Moreover, convective conditions and upward flows caused by the orography have an impact on the performance output as inclined flows result in asymmetric torque distributions. The wind turbine wake and the forest wake mix further downstream, resulting in a fast decay of the turbine wake. The paper also describes how the turbulent flow in the wake changes in the presence of thermal stratification.