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Title:
LAWINE Task A analysis report: on the added benefits of ground-based lidar for turbine load measurements
 
Author(s):
 
Published by: Publication date:
ECN Wind Energy 7-2-2017
 
ECN report number: Document type:
ECN-E--16-051 ECN publication
 
Number of pages: Full text:
30 Download PDF  (2140kB)

Abstract:
Within the project Lawine as part of Task A “Wind resource assessment“ an investigation has been made of the effect of the measured wind resource characteristics by means of LiDAR on the turbine behaviour in terms of mechanical loads. In particular the effect of vertical shear on turbine loads is investigated.

Measurement data from a campaign of 9 months on a 80m hub height turbine, a met mast and a ground based LiDAR were analysed. Distribution of shear in the data was analysed and shear exponent a in the dataset was found to be inversely correlated to turbulence intensity.

Turbine loads measurements for blades, main shaft and tower base were analysed. In the analysis the assumption that blade out-of-plane fatigue bending moment increases with higher shear was investigated. For low TI (0 to 4%) this assumption was confirmed. However for higher TI values the effect of turbulence dominates the blade out-of-plane fatigue load (15% higher out-of-plane EQL when TI increases from 2.5 to 17.5%).

Further observations were made on shear-dependency for blade, main shaft and tower loads. Main shaft average non-rotating bending moment was observed to increase with higher shear (i.e. up to 30% increase was observed). Average static tower base for-aft bending moment was observed to be independent from shear and is expected to be dominated by rotor thrust. Tower base for-aft fatigue equivalent bending moment however decreased with higher a (lower TI), similar to blade out-of-plane EQL.

Ground-based LiDAR measurements are concluded to provide a suitable method for refined determination of turbine loads.


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