The generics of wind turbine nacelle anemometry

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The generics ofwind turbine nacelle anemometry
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Assessment of productive capacity

• Nacelle anemometry serves multiple purposes and
  it is frequently used for verifying productive
  capacity of wind projects. Thus, erection of
  expensive met masts is saved
• Question is it meaningful to use the nacelle
  anemometer?

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The nacelle anemometer is meant to measure the
free wind but the flow around the nacelle is
complicated exposed to numerous sources of
disturbances
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Major influence parameters
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Specific problem

• When we are doing performance verification, what
  are we actually looking for? Answer a possible
  change in power relative to a warranted power
  curve
• Generics while the reading of the nacelle
  anemometer is disturbed by a number of effects,
  some disturbances are related to the wind turbine
  rotors action on the flow
• Calibration components of the nacelle
  anemometer

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Betz 1D rotor model
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Calibration of nacelle anemometer
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Nacelle anemometry what is the generic problem?
Measuring the reference PC,
and calibrating the nacelle anemometer
Measuring the PC in the field,
but the real PC is
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For the 1-D rotor relation between dp and dv

• For the Betz rotor, we have

Assume a change in power relative to warranted
power, at free wind speed u
Measured nacelle wind speed v1
However, presumed free wind speed
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The 1-D generic error of nacelle anemometry

• Resulting change and error in power at wind speed
  u

The error relative to the actual change in power
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The relative generic error for 1-D rotor
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Illustration of generic error
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Siemens, CFD 3-D RANS rotor flow
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DTU CFD 3-D RANS rotor flow
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3-D induction
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Computed and measured performance characteristics
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Comparison of Cp and CT with 1-D ideal Betz
distrib.
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Comparison of Cp and CT with 1-D ideal Betz
distrib.
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Conclusions

• For 1D Betz rotor Nacelle anemometry introduces
  an error which is of the order 75. The error is
  one-sided and may in principle be corrected for
• For 3D rotor the induction close to the rotor
  center and the nacelle is typically small and the
  error is in general terms less. However, the
  gradients is the induction factor are here large,
  which makes the uncertainty of the error large

• These wind speed gradients close to the nacelle
  make it an attraktive option to measure the flow
  speed, say, 10-20m in front of the spinner