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| Titel |
Quantifying error of lidar and sodar Doppler beam swinging measurements of wind turbine wakes using computational fluid dynamics |
| VerfasserIn |
J. K. Lundquist, M. J. Churchfield, S. Lee, A. Clifton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 2 ; Nr. 8, no. 2 (2015-02-23), S.907-920 |
| Datensatznummer |
250116143
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| Publikation (Nr.) |
 copernicus.org/amt-8-907-2015.pdf |
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| Zusammenfassung |
Wind-profiling lidars are now regularly used in boundary-layer meteorology
and in applications such as wind energy and air quality. Lidar wind
profilers exploit the Doppler shift of laser light backscattered from
particulates carried by the wind to measure a line-of-sight (LOS) velocity.
The Doppler beam swinging (DBS) technique, used by many commercial systems,
considers measurements of this LOS velocity in multiple radial directions in
order to estimate horizontal and vertical winds. The method relies on the
assumption of homogeneous flow across the region sampled by the beams. Using
such a system in inhomogeneous flow, such as wind turbine wakes or complex
terrain, will result in errors.
To quantify the errors expected from such violation of the assumption of
horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric
boundary layer, notably stably stratified flow past a wind turbine, with a mean
wind speed of 6.5 m s−1 at the turbine hub-height of 80 m.
This slightly stable case results in 15° of wind direction change
across the turbine rotor disk. The resulting flow field is sampled in the
same fashion that a lidar samples the atmosphere with the DBS approach,
including the lidar range weighting function, enabling quantification of the
error in the DBS observations. The observations from the instruments located
upwind have small errors, which are ameliorated with time averaging.
However, the downwind observations, particularly within the first two rotor
diameters downwind from the wind turbine, suffer from errors due to the
heterogeneity of the wind turbine wake. Errors in the stream-wise component
of the flow approach 30% of the hub-height inflow wind speed close to the
rotor disk. Errors in the cross-stream and vertical velocity components are
also significant: cross-stream component errors are on the order of 15%
of the hub-height inflow wind speed (1.0 m s−1) and errors in the
vertical velocity measurement exceed the actual vertical velocity.
By three rotor diameters downwind, DBS-based assessments of wake wind speed
deficits based on the stream-wise velocity can be relied on even within the
near wake within 1.0 m s−1 (or 15% of the hub-height inflow wind
speed), and the cross-stream velocity error is reduced to 8% while
vertical velocity estimates are compromised. Measurements of inhomogeneous
flow such as wind turbine wakes are susceptible to these errors, and
interpretations of field observations should account for this uncertainty. |
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