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Research Papers

Turbine Inflow Characterization at the National Wind Technology Center

[+] Author and Article Information
George Scott

National Wind Technology Center,
National Renewable Energy Laboratory (NREL),
Golden, CO 80401

Neil Kelley

Consultant Meteorologist,
Boulder, CO 80305

Julie K. Lundquist

Assistant Professor
National Wind Technology Center,
National Renewable Energy Laboratory (NREL),
Golden, CO 80401;
Department of Atmospheric and Oceanic Sciences,
University of Colorado at Boulder,
Boulder, CO 80309

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received February 15, 2012; final manuscript received January 14, 2013; published online May 31, 2013. Assoc. Editor: Christian Masson.

J. Sol. Energy Eng 135(3), 031017 (May 31, 2013) (11 pages) Paper No: SOL-12-1041; doi: 10.1115/1.4024068 History: Received February 15, 2012; Revised January 14, 2013

Utility-scale wind turbines operate in dynamic flows that can vary significantly over time scales from less than a second to several years. To better understand the inflow to utility-scale turbines on time scales from seconds to minutes, the National Renewable Energy Laboratory installed and commissioned two inflow measurement towers at the National Wind Technology Center near Boulder, Colorado, in 2011. These towers are 135 m tall and instrumented with sonic anemometers, cup anemometers, wind vanes, and temperature measurements to characterize the inflow wind speed and direction, turbulence, stability and thermal stratification for two utility-scale turbines. In this paper, we present variations in mean and turbulent wind parameters with height, atmospheric stability, and as a function of wind direction that could be important for turbine operation, and for the persistence of turbine wakes. Wind speed, turbulence intensity, and dissipation are all factors that affect turbine performance. Our results show that these all vary with height across the rotor disk, demonstrating the importance of measuring atmospheric conditions that influence wind turbine performance at multiple heights in the rotor disk, rather than relying on extrapolation from conditions measured at lower levels.

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Figures

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Fig. 1

The National Wind Technology Center. (a) A Siemens utility-scale turbine with 80-m hub height is in the foreground of the picture. The 135-m M4 tower is visible to the left. Photo by Dennis Schroeder, NREL/PIX 19015. (b) Relief map, courtesy of Joe Smith, NREL.

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Fig. 2

Schematic view of the NWTC 135-m M4 inflow monitoring tower. Boom heights are approximate. All booms face 285 deg.

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Fig. 3

Frequency and speed of valid measurements of winds at 80 m above ground, from 1/1/1996 to 12/2031/2010 on the M2 tower. Data are grouped by direction in 7.5 deg bins, and then colored to show wind speeds in 2 m s−1 bins. The distance from the origin shows the cumulative frequency of winds in that direction sector.

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Fig. 4

Comparison of wind speeds measured by LIDAR, sonic anemometers and cup anemometers on the M4 tower

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Fig. 5

Velocity and turbulence profiles for WNW flows (285 deg±15 deg) at 11≤U(76)≤13 m s−1 from 10/7/2011 to 11/7/2011. Data are grouped by stability (Table 2). Markers show mean values; bars show the interquartile range. Data are displaced less than 1 m vertically for visibility.

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Fig. 6

Variation of (a) mean TKE and (b) peak hub-height CTKE at 76 m above ground with |RiS|<2 from 10/7/2011 to 11/7/2011. Data are limited to U(76)>3 m s−1 and flows from the WNW sector (285±15 deg). Upper panels show all data. Lower panels show the statistics of data in each stability class (Table 2), where the divisions between classes are shown in the upper panels with dashed lines. Statistics include the 5th-95th percentile range (vertical line), 25th-75th percentile range (box) and median (horizontal line). Data points in the highest and lowest 5th percentiles are plotted individually.

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Fig. 7

Profiles of velocity and turbulence parameters for SSE flows (175 deg ± 15 deg) at 11≤U(76)≤13 m s−1. Plots use the same data and conventions as Fig. 5.

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Fig. 8

Diurnal cycles of RiS from 3 to 134 m, and z/L at 76 m. Stability classes are listed in Table 2. Data are 10-min average values from 10/7/2011 to 11/7/2011. Data include U(76)>3 m s−1 and exclude the tower wake (75 deg≤WD¯≤135 deg).

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Fig. 9

Comparison of the layer stability measures (a) Ri and RiS and (b) layer stability measure RiS with the normalized Monin–Obukhov length, z/L, at the hub height (76 m). The Businger–Dyer relationship (Eq. (21)) is shown for reference. Data include U(76)>3 m s−1 and exclude the tower wake (75 deg≤WD¯≤135 deg).

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