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An evaluation testbed for wind turbine blade tip designs–baseline case


David A. Johnson, Wind Energy Group, Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo N2L 3 G1, Canada.



A 3.3 m diameter wind turbine rotor has been designed, fabricated, and tested in a large scale university operated indoor wind facility. The rotor was custom designed for operation in the wind facility and allowed for exchangeable blade tips such that various tip designs can be tested for their effects on performance.

The design of the rotor blades utilized the NREL S83X series airfoils, which were blended along the blade. Two-dimensional airfoil performance data were utilized, where available, with models used for post stall performance. The inverse design code PROPID, using Blade Element Momentum (BEM) theory was utilized for the blade design and blade performance was predicted. Subsequently, blades were fabricated in the conventional manner using glass fiber hand laid in computer numerical control (CNC) machined molds.

Turbine power production measurements were completed covering a range of mean wind speeds, 3.6 m/s to 11 m/s nominal, and turbine rotor shaft rotational rates, 100 rpm to 240 rpm. This testing allowed the total power produced by the blades to be determined as a function of input wind speed, as traditionally found in power curves for commercial turbines. The coefficient of power, CP, was determined as a function of the tip speed ratio λ and peak CP was found to approach 0.42 at the design λ of 6.7. At the design shaft speed of 200 rpm, the maximum power produced was 1.45 kW at 11 m/s.

Experimental results were compared with model predictions. The model predicted the performance fairly accurately for λ > 6.5, whereas the model underpredicted performance at high wind speeds and was less successful at predicting CP accurately at low λ. Copyright © 2011 John Wiley & Sons, Ltd.