Doppler lidar scanning of flow over complex terrain

Robert Menke*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesis

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Abstract

Wind energy projects in complex terrain are associated with higher uncertainties compared to projects in flat terrain regarding the estimation of wind conditions. This is due to atmospheric processes that occur over complex or steep terrain, which are difficult to measure, generally not well understood, and are not sufficiently well reproduced by computational models. This thesis presents the results of a Ph.D. study with the focus on flow over complex terrain measured by the means of multiple scanning lidars with the aim to improve the understanding of flow phenomena in complex terrain. The measurements for this project were performed as part of the Perdigão 2017 measurement campaign in Portugal. In total eight synchronized scanning lidars were used to measure flow recirculation zones, atmospheric waves, a wind turbine’s wake, and wind resources along two parallel ridges at Perdigão. The results indicate a systematic trend that recirculation zones are more likely to occur at the northwest end of the valley. Moreover, turbulence levels at the ridges, which are potential locations for wind turbines, are higher when recirculation zones within the valley are present. Atmospheric waves are observed during many nights of the experiment and can cause significant flow acceleration at the downwind ridge. This effect reflects also into the investigation of the wind resources along the ridge, which shows that higher wind speeds are systematically observed downstream during stable atmospheric conditions. Two comparisons of measurement data and the results of computational models are performed. The VENTOSr/M model performs well in reproducing atmospheric wave structures and their time of occurrence. Mean wind speeds predicted by WRF-LES show a high sensitivity to the surface drag parameterization. Overall, this study demonstrates the advantages of scanning lidars to map flow over complex terrain. The insights into flow processes at Perdigão resulting from this study, based on the unique measurement scenarios designed for this work, could not have been gained with traditional profiling instruments.
Original languageEnglish
Place of PublicationRoskilde, Denmark
PublisherDTU Wind Energy
Number of pages87
Publication statusPublished - 2020

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