Predicting the impact of flow field acceleration on wind turbine performance in complex terrain and wind farms

Abstract This work explores the effect of streamwise flow inhomogeneities on power performance and whether this can be described by the same engineering model for both the flow in wind farms and over complex terrain. For this purpose, data from previous computational studies are reanalyzed. Results suggest that in both cases the engineering model is capable of delivering consistent results. Specifically, for complex terrain, they indicate that including a measurement of the undisturbed flow behind the position of a turbine, when it is located on a hill ridge, can improve power performance predictions, as long as the flow does not separate. For a turbine operating in the wake of another turbine within a wind farm, the streamwise acceleration of the free stream due to wake recovery likely influences the turbine’s performance. An implementation of the engineering model into a blade-element momentum (BEM) algorithm in combination with a steady-state implementation of two controllers, one based on the rotor-averaged wind speed (RAWS) and the other one based on the rotor torque, yields similar results in terms of power performance. The modified BEM model results are in good agreement with the reference data obtained from large-eddy simulations (LES) of the Lillgrund wind farm in case of the RAWS controller, while the results for the torque controller diverge from each other. The discrepancy in turbine performance between the two controllers observed in the LES data is unexpected, and cannot be explained within this work. Overall, results appear promising with respect to whether the engineering model can be applied to both cases, the flow in complex terrain and in wind farms, while leaving room for more thorough analyses in future works.