Preprints
https://doi.org/10.5194/wes-2024-18
https://doi.org/10.5194/wes-2024-18
22 Feb 2024
 | 22 Feb 2024
Status: this preprint is currently under review for the journal WES.

Influences of lidar scanning parameters on wind turbine wake retrievals in complex terrain

Rachel Robey and Julie K. Lundquist

Abstract. Scanning lidars enable the collection of spatially resolved measurements of turbine wakes and the estimation of wake properties such as magnitude, extent, and trajectory. Lidar-based characterizations, however, may be subject to distortions due to the observational system. Distortions can arise from the resolution of the measurement points across the wake, the projection of the winds onto the beam, averaging along the beam probe volume, and intervening evolution of the flow over the scan duration. Using a large-eddy simulation and simulated measurements with a virtual lidar model, we assess how scanning lidar systems may influence the properties of the retrieved wake using a case study from the Perdigão campaign. We consider three lidars performing range-height indicator sweeps in complex terrain, based on the deployments of lidars from the Danish Technical University (DTU) and German Aerospace Center (DLR) at the Perdigão site. The unwaked flow, measured by the DTU lidar, is well-captured by the lidar, even without combining data into a multi-lidar retrieval. The two DLR lidars measure a waked transect from different downwind vantage points. In the region of the wake, the observation system interacts with the smaller spatial and temporal variations of the winds, allowing more significant observation distortions to arise. While the measurements largely capture the wake structure and trajectory over its 4–5 D extent, limited spatial resolution of measurement points and volume averaging lead to a quicker loss of the two-lobes in the near wake, smearing of the vertical bounds of the wake (<30 m), wake center displacements up to 10 m, and dampening of the maximum velocity deficit by up to a third. The virtual lidar tool, coupled with simulations, provides a means for assessing measurements capabilities in advance of measurement campaigns.

Rachel Robey and Julie K. Lundquist

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2024-18', Anonymous Referee #1, 17 Mar 2024
  • RC2: 'Comment on wes-2024-18', Anonymous Referee #2, 02 Apr 2024
Rachel Robey and Julie K. Lundquist

Data sets

Supporting simulation and observation files for "Influences of lidar scanning parameters on wind turbine wake retrievals in complex terrain" R. Robey and J. K. Lundquist https://doi.org/10.5281/zenodo.10652098

Model code and software

Virtual Lidar Python R. Robey https://gitlab.com/raro0632/virtual-lidar

Rachel Robey and Julie K. Lundquist

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Short summary
Measurements of wind turbine wakes with scanning lidar instruments contain complex errors. We model lidars in a simulated environment to understand how and why the measured wake may differ from the true wake and validate the results with observational data. The lidar smooths out the wake, making it seem more spread out and the slowdown of the winds smaller. Our findings provide insight into best practices for accurately measuring wakes with lidar and into interpreting observational data.
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