Windfield reconstruction in the induction zone
January 14, 2019
Workshop leader: Nicolai Nygaard (Orsted)
Venue: Hotel Ribera de Triana, Seville, Spain
Nacelle-mounted lidars facing upstream of a wind turbine can measure the wind speed through the induction zone. Several nacelle lidar campaigns have indicated that the induction effect may be felt further upstream of the rotor than is commonly assumed in the design of power curve verification campaigns. To understand the magnitude of the induction effect, the freestream wind speed needs to be established. Since freestream velocity may only be reached beyond the measurement range of the nacelle lidar, an extrapolation based on the lidar measurements is necessary. A wind field model of the induction zone combined with the lidar line of sight wind speeds can be used to perform wind field reconstruction and derive not only the freestream wind speed, but also map the variation of the horizontal wind speed at different distances from the rotor.
No consensus exists on the optimal method for the wind field reconstruction in the induction zone that balances fidelity and simplicity. To take the first steps towards a common understanding in the community a round robin was organized to compare different methods and approaches to the wind field reconstruction problem on a common dataset.
In the round robin preceding the workshop the participants analyzed a dataset of nacelle lidar measurements from an offshore turbine with the aim to reconstruct the wind field in the induction zone upstream of the turbine by using wind speed measurements at multiple ranges. From the reconstructed wind field, the participants derived the freestream wind speed.
The objective of the workshop was to present and discuss the methods and results of the round robin data analysis. By establishing the freestream wind speed, the community will get a better sense of the influence of induction on topics such as power curve verification, wind turbine power performance and wind farm power performance.