This paper investigates the influence of Reynolds number on performance modeling of horizontal axis wind rotors. A procedure for accounting for Reynolds number effects on airfoil section models was developed and implemented for NACA 0012 and NACA 4415 profiles; both of these models is valid through angles of attack up to 90 deg and for Reynolds numbers ranging from 4 × 104 to 3 × 106. These models were incorporated into both a lifting line computer code, LL200R, adapted for this report. This enabled greater certainty to be obtained in evaluating theoretical performance codes with respect to actual data, as well as providing a means by which a parametric analysis of the relative effects of Re changes on rotor performance to be performed. The use of low Reynolds number section data was found to significantly lower the predicted values of power coefficient, particularly at off-design tip-speed-ratios. For symmetrical airfoils, this effect on performance was only significant for low tip-speed-ratios, while cambered airfoils were affected more uniformly at all operating conditions. Changes in performance were induced by parametric variations of wind speed, rotor scale, and rotor generating mode using the Reynolds number dependent section models. Results show that wind speed variations are more significant for smaller rotors at lower wind-speeds, and section models represented at only a single Reynolds number are more suitable for the analysis of constant RPM rotors.
The optimized design of a wind turbine depends on numerous parameters involving the entire machine (rotor, generator, etc.) and on the intended operating environment as described by the wind characteristics as well as on the load or application. This paper presents the design optimization process, identifies and discusses the influence of the various parameters, and then reviews the procedure by looking at two examples. The results of this process emphasize the relative importance of the design on rated wind speed, rotor rpm, generator size, and rotor blade characteristics. These results in general show that wind turbines have been designed for excessively high-rated wind speeds and generator capacities, except for those machines intended for wind farm applications and sites with particularly high winds. Machines designed for residential use should be sized to closely match the expected load and should be rated at a wind speed close to that value where the maximum energy contribution occurs. This wind speed is much lower than the rated wind speed for most currently available machines particularly for regions of relatively low annual mean wind speeds. Simplicity of design leads to a lower cost system, lower maintenance, and operating costs and greater reliability. It is this simply designed and optimized wind turbine that will have lasting success in the commercial market place.
Rockwell I n t e r n a t i o n a l Corporation ' Energy Sys tems Group Rocky F l a t s P l a n t Wind Systems Program P.O. Box 464 Go1 den, Colorado 80401 Subcurl t r-iic t No.
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