This article deals with the influence of yawed inflow conditions on the performance of a single generic 2.4 MW wind turbine. It presents the results of studies performed at the Institute of Aerodynamics and Gas Dynamics by means of computational fluid dynamics, using a fully meshed wind turbine with all boundary layers being resolved. The block-structured flow solver FLOWer is used; a dual-time stepping method for temporal discretization and a second-order Jameson-Schmidt-Turkel method for the calculation of the convective fluxes are applied. All simulations are carried out using a detached eddy simulation approach. In detail, two different wind speeds and a yaw angle range between 50 ı and C50 ı are evaluated in the paper. Based on these data, it is shown that the reduction of power output follows a cosine to the power of X function of the yaw angle. Furthermore, the growing azimuthal non-uniformity of the load distributions with increasing yaw angle magnitude is analysed by spanwise load distributions. As a central influence on the load distributions, the advancing and retreating blade effect is identified. Moreover, the deflection of the wake as a result of the inflow is investigated, and the deflection angles are compared with a modelling approach. A connection line between wake deflection and load asymmetry is drawn. The results are of particular importance for wind park situations with downstream turbines facing the distorted inflow created from upstream ones. 253CFD study on the impact of yawed inflow on a generic wind turbine C. Schulz et al.dynamics solvers using, among others, actuator disc approaches. Several years later, the measurements performed within the Model Experiment in Controlled Conditions (MEXICO) project enlarged the yaw database. 6 This time, a three-bladed model wind turbine was investigated, collecting data of the near wake as well as blade loads and pressure distributions. 6 Within several follow-up projects, the data have been analysed and recent publications 8,9,14 showed reasonable agreement between measurements and simulations. In detail, the simulated wake deflection was investigated and the distortion of the wake was discussed. Even though a great success, none of the measurements were able to describe all effects occurring from yaw misalignment. The reduction of power and mean loads of the turbine, the changing angle of attack over one revolution, the varying induction, the wake distortion and how the different effects correlate with each other. The NASA-Ames measurements cover a wide operational range but provide only little information about the rotor wake. MEXICO and its wide range of particle image velocimetry data provide more information about the near-wake flow field, but lacks the wide range of yaw angles and faces some limitations in turbine set-up as the rotor is not tilted and the tower far downstream the rotor compared with a full-scale turbine. 6,7 Looking at the costs, it is hardly feasible to collect all data needed to investigate most of the yaw effects and cover...

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The current study describes analyses of the WINSENT wind energy test site located in complex terrain in Southern Germany by highly resolved numerical simulations. The resolved atmospheric turbulence is simulated with Delayed Detached Eddy Simulations by the flow solver FLOWer without consideration of the research wind turbines. The mean inflow and wind direction of the analysed time period is provided by precursor simulations of project partners. The simulation model chain consists of three codes with different time scales and resolutions. The model chain provides a data transfer from mesoscale WRF simulations to OpenFOAM. As a next step OpenFOAM provides inflow data in the valley of the terrain site for the present FLOWer simulations, the code with the highest resolution in space and time. The mean velocity field provided by OpenFOAM is superimposed with fluctuations that are based on measurements to obtain the small turbulent scales within the FLOWer simulations, which the previous tools of the model chain can not resolve. Comparisons with the two already installed met masts clarify that the current FLOWer simulations provide an adequate agreement with measured data. The results are verified with the application of a second simulation, in which a homogeneous velocity profile is superimposed with turbulence. Thus, comparisons with measured data showed that the benefit of using the inflow data of this model chain is especially evident near the ground.

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.

Abstract. This paper shows high-fidelity Fluid Structure Interaction (FSI) studies applied on the research wind turbine of the WINSENT project. In this project, two research wind turbines are going to be erected in the South of Germany in the WindForS complex terrain test field. The FSI is obtained by coupling the CFD URANS/DES code FLOWer and the multiphysics FEM solver Kratos, in which both beam and shell structural elements can be chosen to model the turbine. The two codes are coupled in both an explicit and an implicit way. The different modelling approaches strongly differ with respect to computational resources and therefore the advantages of their higher accuracy must be correlated with the respective additional computational costs. The presented FSI coupling method has been applied firstly to a single blade model of the turbine under standard uniform inflow conditions. It could be concluded that for such a small turbine, in uniform conditions a beam model is sufficient to correctly build the blade deformations. Afterwards, the aerodynamic complexity has been increased considering the full turbine with turbulent inflow conditions generated from real field data, in both a flat and complex terrains. It is shown that in these cases a higher structural fidelity is necessary. The effects of aeroelasticity are then shown on the phase-averaged blade loads, showing that using the same inflow turbulence, a flat terrain is mostly influenced by the shear, while the complex terrain is mostly affected by low velocity structures generated by the forest. Finally, the impact of aeroelasticity and turbulence on the Damage Equivalent Loading (DEL) is discussed, showing that flexibility is reducing the DEL in case of turbulent inflow, acting as a damper breaking larger cycles into smaller ones.