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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/acp-2018-847
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-847
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Sep 2018

Research article | 10 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Characterization of flow recirculation zones in complex terrain using multi-lidar measurements

Robert Menke1, Nikola Vasiljević1, Jakob Mann1, and Julie K. Lundquist2,3 Robert Menke et al.
  • 1Technical University of Denmark - DTU Wind Energy, Fredriksborgvej 399, Building 118, 4000 Roskilde, Denmark
  • 2Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA
  • 3National Renewable Energy Laboratory, Golden, Colorado, USA

Abstract. Because flow recirculation can generate significant amounts of turbulence, it can impact the success of wind energy projects. This study uses unique Doppler lidar observations to quantify occurrences of flow recirculation on lee sides of ridges. An extensive dataset of observations of flow over complex terrain is available from the Perdigão-2017 field campaign over a period of three months. The campaign site was selected because of the unique terrain feature of two nearly parallel ridges with a valley-to-ridge-top height difference of about 200m and a ridge-to-ridge distance of 1.4km.

Six scanning Doppler lidars probed the flow field in several vertical planes orthogonal to the ridges using range-height-indicator scans. With this lidar setup, we achieved vertical scans of the recirculation zone at three positions along two parallel ridges. We construct a method to identify flow recirculation zones in the scans, as well as define characteristics of these zones. According to our data analysis, flow recirculation, with reverse flow wind speeds greater than 0.5ms−1, occurs over 50% of the time when the wind direction is perpendicular to the direction of the ridges. Atmospheric conditions, such as atmospheric stability and wind speed, affect the occurrence of flow recirculation. Flow recirculation occurs more frequently during periods with wind speeds above 8ms−1. Recirculation within the valley affects the mean wind and turbulence fields at turbine heights on the downwind ridge in magnitudes significant for wind resource assessment.

Robert Menke et al.
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Robert Menke et al.
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This research utilizes several months of lidar measurements from the Perdigão 2017 campaign to investigate flow recirculation zones that occur at the two parallel ridges at the measurement site in Portugal. We found that recirculation occurs in over 50 % of the time when the wind direction is perpendicular to the direction of the ridges. Moreover, we show three-dimensional changes of the zones along the ridges and the implications of recirculation on wind turbines that are operating downstream.
This research utilizes several months of lidar measurements from the Perdigão 2017 campaign to...
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