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Lillgrund TI Spacing

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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 case based on the actual operational Lillgrund wind farm in which there are multiple turbines interacting within an array.  This benchmark aims to test a wake/atmospheric model to reproduce the maximum power deficit of the second turbine in a row as a function of spacing and turbulence intensity.

Objectives

Demonstrate how wake models perform and capture the wake formation and merging process in the presence of atmospheric shear and turbulence within a large modern wind farm composed of modern multimegawatt turbines. 

Data Accessibility

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

Input data

The conditions for simulating the LillgrundTISpacing case are:

  • Location: 55.52° N, 12.78° E
  • Hub height turbulence intensity:  This quantity is defined as ‹u’u’›1/2/U0 where ‹u’u’›1/2 is the streamwise velocity variance and U0 is the mean hub-height wind speed.  Vary this quantity from 2% to 12%.
  • Surface roughness:  z0 = 0.0001 m unless a different value is needed by your simulation method to produce the desired hub-height turbulence intensity.
  • Hub height mean wind speed: 9.0 m/s.
  • Spacing:  Use spacings of 3.3D, 4.3D, 4.8D, and 7.1D.
  • Stability: Assume neutral stability because stability is not given by Dahlberg (2009) or Bergström (2009) and data is averaged over a long time period.
  • Turbine model:  Siemens SWT-2.3.93.
    • The basic turbine characteristics of coefficient of power and thrust versus wind speed are given in the test case guide (Figure 2) and in the file SWT-2.3-93.txt. 
    • If a more detailed turbine model is used that requires blade and control system information, a detailed generic turbine characterization representative of the actual turbine and tuned to the Cp and CT data given in SWT-2.3-93.txt is given by Churchfield (2013).

Validation data

The validation data consists of maximum observed power deficit as a function of inflow turbulence intensity at hub height and wind turbine spacing as shown in Figure 1 below.

Figure 1   Maximum power deficit of second turbine in row as a function of inflow turbulence intensity and spacing.

Model runs

The participant should use a domain size sufficient for his or her model to work properly and devoid of spurious boundary effects.  Choose as many combinations within the turbulence intensity range and set of spacings to simulate.  The line from turbine 1 to turbine 2 should be parallel to the mean hub height wind direction.

Output data

Output data to be reported are normalized average power deficit of the second turbine in which the averaging period is at least 10 minutes.  The power deficit should be reported as deficit = Pwaked / Punwaked, where P is time-averaged power output.

The file output should be of the form:

  • Deficit data

LillgrundTISpacing_UserID_ModelID_deficit_spacing#.txt

Provide a separate file for each spacing used and replace the “#” after “spacing” in the file name with the numerical spacing value.  A multiple column list of power deficit as a function of turbulence intensity.  Each row (below the first row header) corresponds to a different inflow turbulence intensity.  An example is shown below.

Turbulence intensity, deficit
0.02, 0.454

0.07, 0.544
0.08, 0.548
0.09, 0.564

0.12, 0.654

Remarks

None.