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Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar

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  • 1 Wind Energy Department, Risoe National Laboratory, Roskilde, Denmark
  • | 2 Ecofys bv, Utrecht, Netherlands
  • | 3 School of Engineering, Robert Gordon University, Schoolhill, Aberdeen, United Kingdom
  • | 4 Atmospheric Science Program, Department of Geography, Indiana University at Bloomington, Bloomington, Indiana
  • | 5 ForWind—Center for Wind Energy Research, Institute of Physics, University of Oldenburg, Oldenburg, Germany
  • | 6 Wind Energy Department, Energy Research Centre of the Netherlands, Petten, Netherlands
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Abstract

This paper gives an evaluation of most of the commonly used models for predicting wind speed decrease (wake) downstream of a wind turbine. The evaluation is based on six experiments where free-stream and wake wind speed profiles were measured using a ship-mounted sodar at a small offshore wind farm. The experiments were conducted at varying distances between 1.7 and 7.4 rotor diameters downstream of the wind turbine. Evaluation of the models compares the predicted and observed velocity deficits at hub height. A new method of evaluation based on determining the cumulative momentum deficit over the profiles is described. Despite the apparent simplicity of the experiments, the models give a wide range of predictions. Overall, it is not possible to establish any of the models as having individually superior performance with respect to the measurements.

++ Current affiliation: Faculty of Engineering, Technological Education Institute of Western Macedonia, Koila, Kozani, Greece

## Current affiliation: ISET e.V., Kassel, Germany

Corresponding author address: R. J. Barthelmie, Institute for Energy Systems, School of Engineering and Electronics, University of Edinburgh, EH9 3JL, United Kingdom. Email: R.Barthelmie@ed.ac.uk

Abstract

This paper gives an evaluation of most of the commonly used models for predicting wind speed decrease (wake) downstream of a wind turbine. The evaluation is based on six experiments where free-stream and wake wind speed profiles were measured using a ship-mounted sodar at a small offshore wind farm. The experiments were conducted at varying distances between 1.7 and 7.4 rotor diameters downstream of the wind turbine. Evaluation of the models compares the predicted and observed velocity deficits at hub height. A new method of evaluation based on determining the cumulative momentum deficit over the profiles is described. Despite the apparent simplicity of the experiments, the models give a wide range of predictions. Overall, it is not possible to establish any of the models as having individually superior performance with respect to the measurements.

++ Current affiliation: Faculty of Engineering, Technological Education Institute of Western Macedonia, Koila, Kozani, Greece

## Current affiliation: ISET e.V., Kassel, Germany

Corresponding author address: R. J. Barthelmie, Institute for Energy Systems, School of Engineering and Electronics, University of Edinburgh, EH9 3JL, United Kingdom. Email: R.Barthelmie@ed.ac.uk

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