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Sexbierum

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Data Provider: 

The data has been extracted from Cleijne (1993, 1992).

Data accesibility: 

The test case is offered to participants of the IEA Task 31 Wakebench.

Site Description: 

The measurements were carried out in 1992 at the Dutch Experimental Wind Farm at Sexbierum, which is in the northern part of The Netherlands about 4 km from the shore.  The wind farm is in flat, homogeneous terrain characterized by grassland.  The wind farm contains 18 HOLEC turbines each producing 310 kW rated power and with a rotor diameter of 30 m and a hub height of 35 m.  The turbines are arranged in a 3 × 6 array as shown in Figure 1.

Figure 1: Layout of the Dutch Experimental Wind Farm at Sexbierum taken from Cleijne (1992, 1993).

Instrumentation: 

There are 7 meteorological masts around the wind farm, as shown in Figure 1, each having an anemometer and wind vane at 35 m.  Measurements are sampled at 1 Hz. 

There are also three mobile masts used for detailed wake measurements, as shown in Figures 2 and 3.  Mastbhas 3-component propeller anemometers at 47 m, 35 m, and 23 m above the ground.  It also has cup anemometers at 41 m and 29 m.  Mastsaandchave 3-component propeller anemometers at 35 m.  Measurements on the mobile masts are taken at 4Hz. 

For the single wake case, the mobile masts were installed on a line between turbines T18 and T27.  Masts ba, and c are located 2.5 D, 5.5 D, and 8 D downwind of turbine T18, respectively.

For the double wake case, the mobile masts were installed in a line perpendicular to the line between turbines T38 and T36 120 m (4D) downwind of turbine T37 as shown in Figure 3.  Mast bis located on the turbine T38—T36 center line, mast a and mast c are offset 12 m and 30 m, respectively, from that center line.

Figure 2: A side view showing the locations of mobile masts and the positions of instrumentation for single wake case taken from Cleijne (1993).

Figure 3: A front (top) and plan (bottom) view showing the locations of mobile masts and the positions of instrumentation for double wake case taken from Cleijne (1992).

Measurement Campaign: 

The measurement campaign was carried out over the course of 1992.  There were two measurement campaigns: one focusing on the single wake, and the other on the double wake situation. 

  • The focus of the single wake measurement campaign (Cleijne, 1993) was on the wake generated by turbine T18 when the wind was blowing in the general direction of turbine T18 to T27.  Measurements were taken at 2.5 rotor diameters (D), 5.5 D, and 8 D downstream of turbine T18, where D = 30 m.
  • The focus of the double wake measurement campaign (Cleijne, 1992) was on turbines T38, T37, and T36, which are separated by 5 D, and the double wake effect produced by turbines T38 and T37.

The 1 Hz and 4 Hz data were processed to obtain 1 minute averages. Those 1 minute averages were then further manipulated to obtain 3 minute averages so that coherence between wind fluctuations measured at the meteorological masts and turbine/wake response is captured.

Remarks: 

Although this dataset is from the early 1990s, it is unique in that it contains detailed profiles of velocity components, turbulent kinetic energy, and Reynolds stresses within both a single and a double wake. The turbine rotor diameters are fairly small compared to modern turbines, but much larger than wind tunnel experiment rotors. The turbines at Sexbierum are fully characterized by Bulder (1993).  This is a good case to examine the ability of various models to represent wakes and wake merging.

References: 

Cleijne, J.W., 1993, Results of Sexbierum Wind Farm; Single Wake Measurements, TNO Report 93-082.

Cleijne, J.W., 1992, Results of Sexbierum Wind Farm; Double Wake Measurements, TNO Report 92-388.

Bulder, B.H., 1993, Mechanical Loads Predictions for the WPS-30 Wind Turbine in the Sexbierum Wind Farm, ECN-C—93-078.

NDA: 

Not applicable.