Offshore wind turbines are deployed in large farms, where wind farm aerodynamics plays an important role in the overall performance. The research at ECN is especially strong through the combination of experimental and theoretical research.

Theoretical modelling. Computational fluid dynamics (CFD) - numerical solutions of the Navier Stokes equations - are applied for the further understanding of flow phenomena in wind farms. The research comprises the development of validated wake models and CFD wind farm models using commercial solvers as well as the development of dedicated wind farm aerodynamics CFD solvers. Interesting model challenges are combined, such as the modelling of the atmospheric boundary layer, the flow inside the wind farm, the modelling of the turbine including its control, the wind farm control as well as the optimisation of this system.

The FarmFlow program is a validated tool developed by ECN to calculate the wake effects of large offshore wind farms. The FarmFlow tool allows the user to accurately optimise the lay-out of the wind farm with respect to power output and, in conjunction with an aero-elastic codes, the possibility to perform design calculations on wind turbines that are placed in wind farms.

Experiments include tunnel measurements and field experiments that include the ECN scale wind farm and the ECN full scale wind farm measurements. Several wind tunnel measurement campaigns have been performed dedicated to the understanding of the wind farm effects. These have been performed in the boundary layer wind tunnel of TNO Apeldoorn. ECN has made operational a unique scale wind farm test facility consisting of 10kW turbines that can be fully controlled to fulfil the experimental requirements. The scale wind farm is used for research on wind farm aerodynamics and gives excellent opportunities to validate the numerical codes. Furthermore, in the scale wind farm advanced wind farm control algorithms are demonstrated. The ECN full scale research wind farm exists of five 2.5MW N80 wind turbines. These full scale turbines are continuously used for a large variety of experiments and offer excellent opportunities to demonstrate aerodynamic improvements.

The combination of numerical and experimental research is the key to acquire new insights and develop new models. These will better describe the effects of wind farm aero-dynamics on the performance of wind farms. Furthermore, these models are used to develop concepts to optimise wind farms in terms of increased production and reduced mechanical loads.