CFD Performance Analyses of Wind Turbines Operating in Complex Environments

This paper presents results from CFD simulations of wind turbines performed within the project WEALoads. The focus of this project is devoted to the unsteady load response of wind turbines under realistic environmental conditions, as for example operation inside of a wind farm or in complex terrain which are both subject of this paper. The first case shall investigate the behavior of a wind turbine operating half in the wake of an upstream turbine, in order to derive the dominant interference effects between wind turbines. Secondly, a wind turbine shall be analyzed which is sited on a hill to elaborate the main effects arising from the interaction of the atmospheric boundary layer with the hill and finally the wind turbine. Both simulations were performed using the flow solver FLOWer from DLR (German Aerospace Center) and the Detached Eddy Simulations (DES) approach. Results of the flow fields are shown in terms of wake development, as well as turbulence intensity. Regarding the case of the turbine sited in complex terrain, a site assessment study has been performed, in order to find designated positions where maximum power output of the wind turbine can be expected. Finally, for both cases, blade load evaluations showed significant influence of the operating environment. For the case of the interacting turbines the load response of the shadowed turbine showed a massively asymmetric loading of the entire rotor. For the turbine located on the hill, significant augmentation of the entire load level could be observed.