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The Science of Making Torque from Wind (TORQUE 2018)

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Room: BL.27.0.1
Chaired by: Sandrine Aubrun | EC Nantes
Topic: MET. Measurement and Experimental Techniques
Form of presentation: Oral
Duration: 90 minutes

Authors:
Norman Wildmann

Abstract:
The understanding and modelling of wakes of wind energy converters (WEC) is highly relevant to wind-energy research. In wind parks, wakes interact with WEC downstream, causing higher loads and lower energy yield compared to the operation in the free stream. In this study, long-range lidar instruments are used to detect and analyse a wake of a single WEC in complex terrain in different atmospheric stability regimes. The special orography of two parallel mountain ridges at the Perdigão 2017 experiment allowed to place two lidars in a coplanar set-up and retrieve horizontal as well as vertical wind speed in a cross-section of the valley between the ridges which is in-plane with the WEC. In cases of main wind direction, which is parallel to the lidar scans, the wake’s propagation can thus be measured far downstream in the valley. A wake tracking algorithm is proposed to automatically detect the wake center in the lidar scans. Wind speed deficits and wake deflection is quantified and categorized to stability regimes. A careful uncertainty estimation is done for the coplanar wind retrieval.

Authors:
Ioanna Karagali, Andrea N Hahmann, Merete Badger, Charlotte Hasager, Jakob Mann

Abstract:
The New European Wind Atlas (NEWA) is a joint research effort from eight European countries, co-funded under the ERANET Plus Program. The final aim is the creation and publication of an electronic European wind atlas. An offshore wind atlas extending 100 km from the European coasts is foreseen within the project, based on mesoscale modelling and various observational datasets. Satellite wind retrievals from scatterometers and Synthetic Aperture Radar (SAR) instruments are used to validate offshore modelled wind fields and identify the optimal model set-up parameters. The aim of this study is to present the initial outputs from the offshore wind atlas produced by the Weather & Research Forecasting (WRF) model, still in pre-operational phase, the METOP-A/B Advanced Scatterometer (ASCAT) and SAR derived winds. Different experiments were set-up to evaluate the model sensitivity for the various domains covered by the NEWA offshore atlas. ASCAT winds are utilised to assess the performance of the WRF offshore atlases. In addition, ASCAT winds were used to create an offshore atlas covering the years 2007 to 2016, where various spatial wind characteristics, such as channelling and lee effects from complex coastal topographical features, were visualised.

Authors:
Anantha Padmanabhan Kidambi Sekar, Marijn Floris van Dooren, Torben Mikkelsen, Mikael Sjöholm, Poul Astrup, Martin Kühn

Abstract:
The fast LINCOM method is a set of linearised flow equations that enables the reconstruction of a 3D wind field from a large set of non-parallel radial wind speed measurements. An evaluation is performed with simulated and full scale boundary layer wind field measurements. The model is first tested on deterministic wind fields to evaluate its performance under known conditions. Line-of-sight measurements are extracted from a virtual SpinnerLidar placed in an LES wind field and then the LINCOM method is applied and validated. Finally, the wind field reconstruction methodology is experimentally evaluated with lidar measurements from the IRPWIND joint experiment SCANFLOW campaign where SpinnerLidar line-of-sight inflow measurements from the nacelle of a test turbine was used to reconstruct 3D wind fields. These reconstructed wind fields are then compared with simultaneously measured independent full-scale 3D short-range WindScanner wind data.

Authors:
Matthias Kretschmer, Frederik Schwede, Ricardo Faerron Guzmán, Sarah Lott, Po Wen Cheng

Abstract:
Dependence between fatigue loads on a wind turbine located in an offshore wind farm and atmospheric stability was analysed by using measurement data of alpha ventus. An investigation of the fatigue load spectra of the wind turbines was performed enabling a detailed evaluation besides the damage equivalent load. Therefore, load spectra of a turbine in free-stream and a turbine experiencing wake inflow conditions were compared. Atmospheric stability was taken into account by means of the Bulk Richardson number. It was shown, how atmospheric stability affects load spectra of tower base and blade root bending moment. Hereby, it was found that few events of high fatigue loading increase the damage equivalent load (DEL) substantially, especially in unstable conditions.

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