Terrain Induced Loads on Pitch Regulated Wind Turbines

The loads on wind turbines erected in homogeneous terrain are to some extent believed to be well-known and predictable using aeroelastic load prediction codes. This is not the case for complex terrain and the design loads for wind turbines erected in this type of terrain often are derived from the design rules for wind turbines erected in homogeneous terrain.
The present work concerns the loads for pitch-regulated wind turbines in different types of terrain. It is the objective to identify the important load-generating mechanisms in complex terrain in order to be able to predict the loads for wind turbines erected in these types of terrain.
The experimental part of the investigation is based no measurements on a Vestas V39-500 kW wind turbine in flat terrain in Denmark and in very complex mountainous terrain in the Sky River wind farm in California. It is not possible to identify the effects of the terrain in a straightforward way from the experiments alone, and it is necessary to combine the experiments with load predictions, which is based on two different aeroelastic codes.
Based on the experimental analysis, the assumptions for the load predictions are identified through a detailed analysis of the wind fields, and load predictions are performed for the wind turbine in Denmark and California, respectively. Afterwards, the load prediction codes are used to generalize the findings and clarify the effects of the different types of terrain on the wind turbine loadings.
The investigation illustrates the high differences in inflow conditions between different types of terrain, and the resulting differences in the wind turbine loads. It is concluded that it is possible to predict the loads in both homogeneous and complex terrain if the modelling of the wind fields are appropriate.