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Sexbierum Single Wake Neutral

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Scope

The benchmark is open to participants of the Wakebench project using wake and, possibly, atmospheric boundary layer models. This is a realistic wake case measured at the Dutch Experimental Wind Farm at Sexbierum.  It focuses on the single wake case, which is a good “building-block” to the double wake case (Sexbierum_DoubleWakeNeutral).

Objectives

Demonstrate how wake models perform and capture the wake formation and evolution process in the presence of atmospheric shear and turbulence.

Data Accessibility

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

Input data

The conditions for simulating the Sexbierum double wake are:

  • Hub height mean wind speed: U0 = 8.0 m/s
  • Hub height turbulence intensity: ‹u’u’›1/2/U0 = 0.135
  • Aerodynamic roughness height: z0 = 0.047 m
  • Location: 53.22° N, 5.48° E
  • Wind direction: -30° to +30°, where 0° is the direction of the line between turbines T18 and T27 as shown in Figure 4.
  • Stability: This is not given by Cleijne (1992) and data is averaged over a long (months) time period, so assume neutral stability.
  • Turbine model:  WPS 30.  See attached Cp and Ct curves and consult Bulder (1993) for specifications.

Figure 4: Definition of the coordinate system taken from Cleijne (1992, 1993).

Validation data

The validation data consists of mean and turbulent inflow point measurements and wake profiles (profiles as a function of wind direction). The wake profiles are taken at three different heights above, at, and below hub height at 2.5 D and at hub height at 5.5 D and 8 D.

Model runs

The participant should use a domain size sufficient for his or her model to work properly and devoid of spurious boundary effects. A single case may be run with measurements taken along the arcs that the meteorological masts lie upon relative to the wake centerline fixed coordinate system, as shown in Figure 5.

Figure 5: Arcs upon which to take measurements. The sector width is +/- 30°.

Output data

1. For direct comparison to data (output1.dat):  Provide values of the mean velocity components (U,V, and W), turbulent kinetic energy (tke), and if possible the three velocity component variances (‹u’u’›1/2, ‹v’v’›1/2, and ‹w’w’›1/2) and the three Reynolds shear stress components (‹u’v’›, ‹u’w’›, ‹v’w’›) at the sensor locations on mobile mast b and on the single sensor locations on masts a and c(see Figure 2).  Also provide the values of mean wind speed (U0) and turbulence intensity (I) at the three sensor location of meteorological mast 4 (see Figure 1). Provide the average power production of turbine T18.  Use the file naming and format convention described in the Windbench user's guide.

2. Additional data for model intercomparison (output2.dat):  Vertical lines of mean (UV, and W) and turbulent (tke, ‹u’u’›1/2, ‹v’v’›1/2, ‹w’w’›1/2, ‹u’v’›, ‹u’w’›, and ‹v’w’›) data that extend from the surface to 1D above to upper extent of the rotor with sufficient resolution to show the profiles at 2.5D, 5.5D, and 8D downstream and aligned with the wake center (0°) (see Figure 6).

Figure 6: Vertical lines of data extraction for output2.dat.

3. Additional data for model intercomparison (output3.dat):  Horizontal lines of mean (UV, and W) and turbulent (tke, ‹u’u’1/2, ‹v’v’1/2, ‹w’w’1/2, ‹u’v’›, ‹u’w’›, and ‹v’w’›) data that extend from 3D upstream to 8D downstream of the turbine and passing through the center of the rotor, ¼D above the center of the rotor, and ¼D below the center of the rotor and aligned with the 0° direction (see Figure 7).

Figure 7: Horizontal lines of data extraction for output3.dat.

Remarks

The velocity vector is based in a wind-direction-local coordinate system, as shown in Figure 4. Take care to rotate the output into this coordinate system for each wind direction you run.

Terms andConditions

Not applicable.