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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2018-55
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 Mar 2018
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.
Wind Turbine Wake Measurements with Automatically Adjusting Scanning Trajectories in a Multi-Doppler Lidar Setup
Norman Wildmann1, Nikola Vasiljevic2, and Thomas Gerz1 1Deutsches Zentrum für Luft- und Raumfahrt e.V., Münchner Str. 20, Oberpfaffenhofen, Germany
2DTU Wind Energy, Technical University of Denmark, Frederiksborgvej 399, Building 118-VEA, 4000 Roskilde, Denmark
Abstract. In the context of the Perdigão 2017 experiment, the German Aerospace Center (DLR) deployed three long-range scanning Doppler lidars with the dedicated purpose of investigating the wake of a single wind turbine at the experimental site. A novel method was established to investigate wake properties with ground-based lidars over a wide range of wind directions. For this method, the three lidars, which were space- and time-synchronized using the WindScanner software, were programmed to measure with crossing beams at individual points up to ten rotor diameters downstream the wind turbine. Every half hour, the measurement points were adapted to the current wind direction to obtain a high availability of wake measurements in changing wind conditions. The linearly independent radial velocities where the lidar beams intersect allow the calculation of the wind vector at those points. Two approaches to estimate the prevailing wind direction were tested throughout the campaign. In the first approach, VAD scans of one of the lidars were used to calculate a five-minute average of wind speed and wind direction every half hour, whereas later in the experiment, five-minute averages of sonic anemometer measurements of a meteorological mast close to the wind turbine became available in real-time and were used for the scanning adjustment. Results of wind speed deficit measurements are presented for two measurement days with varying westerly winds and it is evaluated how well the lidar beam intersection points match the actual wake location. The new method allowed to obtain wake measurements over the whole measurement period, whereas a static scanning setup would only have captured short periods of wake occurrences. The analysed cases reveal that state-of-the-art engineering models for wakes underestimate the actual wind speed deficit.
Citation: Wildmann, N., Vasiljevic, N., and Gerz, T.: Wind Turbine Wake Measurements with Automatically Adjusting Scanning Trajectories in a Multi-Doppler Lidar Setup, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-55, in review, 2018.
Norman Wildmann et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Reviewer', Anonymous Referee #1, 23 Mar 2018 Printer-friendly Version 
AC1: 'Reply to review #1', Norman Wildmann, 18 May 2018 Printer-friendly Version 
 
RC2: 'Missing thermal stability information', Anonymous Referee #2, 23 Mar 2018 Printer-friendly Version 
AC2: 'Reply to review #2', Norman Wildmann, 18 May 2018 Printer-friendly Version 
Norman Wildmann et al.
Norman Wildmann et al.

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Short summary
Wind turbines extract energy from the flow which manifests in a region of lower wind speeds and increased turbulence downstream of the rotor, the so-called wake. Understanding the characteristics of the wake is a key challenge for wind energy research. A new strategy to measure the wind in the wake with three synchronized lidar instruments is presented. The measurement points are automatically adapted to the prevailing wind direction to get a continuous monitoring of wake properties.
Wind turbines extract energy from the flow which manifests in a region of lower wind speeds and...
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