A study of the near wake of a model wind turbine using particle image velocimetry

• Main Author: Whale, Jonathan
• Published: University of Edinburgh 1996
• Subjects: 620.106
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663677

Whole-field velocity and vorticity measurements have been obtained in the near wake of a model wind turbine using the technique of Particle Image Velocimetry (PIV). The experiments were conducted in a water channel with the turbine operating over a range of tip speed ratios, λ = 1.6 - 8. These were tip speed ratios pertinent to full-scale turbine operation and assured that the ratio of velocities at a full-scale machine were reproduced at the model. The corresponding range of Reynolds numbers, based on blade chord, was 2,600 - 16,000. Results have been presented for both a 2-blade flat-plate rotor and a 3-blade model replica of a full-scale wind turbine. An analysis of the velocity structure of the wakes produced mean and turbulent velocity profiles and made comparisons with results from both full-scale measurements and wind tunnel tests. Scale effect was isolated as a limiting factor in extrapolating velocity deficits from the PIV results to full-scale. An analysis of the vorticity structure identified behaviour in the wake which influenced the geometry and stability of the vortex system. The PIV images confirmed that the simple models currently being used by the wind turbine industry for design purposes are fundamentally flawed. Comparisons were made with simulations from a sophisticated vortex wake code being developed at the University of Stuttgart. Significant discrepancies were identified in wake development. The study is viewed as a first step in determining the detailed physical processes governing wind turbine wake behaviour in order that advanced rotor performance methods may be developed.