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Abstract. The influence of turbulent inflow, as it occurs in complex terrain, on the unsteady surface pressure distributions on a wind turbine is investigated numerically. A method is presented that enables an accurate reproduction of the inflow to the turbine in the complex terrain in Perdigao, Portugal. For this purpose, a precursor simulation with the steady-state atmospheric computational fluid dynamics (CFD) code E-Wind and a high-resolution Delayed Detached Eddy Simulation (DDES) with FLOWer is performed. The conservation of the flow field is validated by a comparison with measurements from the 2017 field campaign in Perdigao. Then, the resolved fluid-structure coupled generic wind turbine I82 is included in the FLOWer simulation to investigate the impact of the complex terrain inflow on the surface pressure fluctuations on tower and blades. A comparison with simulations of the same turbine in flat terrain with simpler inflows shows that the turbine in complex terrain has a significantly different vortex shedding at the tower, which dominates the periodic pressure fluctuations at the tower sides and back. However, the dominant source of periodic pressure fluctuations on the upper part of the tower, the blade-tower interaction, is hardly altered by the terrain flow. The pressure fluctuations on the blade have a rather broadband characteristic, caused by the interaction of the leading edge with the inflow turbulence. In general, it is shown that a sophisticated DDES of the complex terrain plays a decisive role in the unsteady aerodynamics of the turbine, due to its specific flow characteristic.

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Abstract. The surface pressure fluctuations, which are a source of low-frequency noise emissions, are numerically investigated on a 2 MW wind turbine under different inflow conditions. In order to evaluate the impact of a complex-terrain flow, a computational setup is presented that is aimed at reproducing a realistic flow field in the complex terrain in Perdigão, Portugal. A precursor simulation with the steady-state atmospheric computational fluid dynamics (CFD) code E-Wind is used, which was calibrated with meteorological (met) mast data to generate a site- and situation-specific inflow for a high-resolution delayed detached-eddy simulation (DDES) with FLOWer. A validation with lidar and met mast data reveals a good agreement of the flow field in the vicinity of the turbine in terms of mean wind speed and wind direction, whereas the turbulence intensity is slightly underestimated. Further downstream in the valley and on the second ridge, the deviations between simulation and measurement become significantly larger. The geometrically resolved turbine is coupled to the structural solver SIMPACK and simulated both in the complex terrain and in flat terrain with simpler inflows as reference. The surface pressure fluctuations are evaluated on the tower and blades. It is found that the periodic pressure fluctuations at the tower sides and back are dominated by vortex shedding, which strongly depends on the inflow and is reduced by inflow turbulence. However, the dominant pressure fluctuations on the upper part of the tower, which are caused by the blade–tower interaction, remain almost unchanged by the different inflows. The predominant pressure fluctuations on the blades occur with the rotation frequency. They are caused by a combination of rotor tilt, vertical wind shear and inclined flow and are thus strongly dependent on the inflow and the surrounding terrain. The inflow turbulence masks fluctuations at higher harmonics of the blade–tower interaction with its broadband characteristic caused by the interaction of the leading edge and the inflow turbulence.

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