In a continuing effort to enhance the performance of small wind energy syste~, one root airfoil and three primary airfoils were specifically designed for smal~ honzonta/ axis wind turbines. These airfoils are intended primarily for 1-5 kW varrable-speed wind turbines for both conventional (tapered/twisted) or pu/truded blades. The four airfoils were wind-tunnel tested at Reynolds numbers between 100,000 and 500.~. Tests with simulated leading-edge roughness were also conducted. The results mdtcate that small variable-speed wind turbines should benefit from the use of the n~w aiifoils which provide enhanced ilft-to-drag ratio perfonnance as compared wllh previously existing airfoils.
ForewordPrevious phases of experimenting with the Combined Experiment Rotor (CER) of the National Renewable Energy Laboratory (NREL) have provided test results from two constant-chord blade sets. The first blade set had no twist whereas the second had twist. As the next step, the design of a tapered/twisted blade for the CER was contracted out to the Department of Aeronautical and Astronautical Engineering of the University of Illinois at Urbana-Champaign. This blade design work consisted of a systematic trade-off study where many blade configurations were compared to determine how much the design constraints affected blade performance. Based on the results of the tradeoff study, a blade having a linear taper and nonlinear twist, and that uses the S809 airfoil, was selected as the new CER blade. An extended version of this blade was also designed for a two-bladed rotor configuration. PrefaceA tapered/twisted blade set was designed for the Combined Experiment Rotor (CER) of the National Renewable Energy Laboratory. The objective was to build on the knowledge base of the previous CER tests conducted with constant-chord/untwisted blades and constant-chord/twisted blades. Such CER tapered/twisted blades will yield performance that is more representative of commercial blades. In addition, these new blades will continue to satisfy the scientific needs for fundamental research in rotor aerodynamics.This blade design work for the CER was performed during the summer of 1997 while the first author was at the National Wind Technology Center. The authors would like to thank NREL for providing funding under subcontract XAF-4-14076-03 and the opportunity to design new blades for the CER. Also, the authors would like to thank James L. Tangler SummaryA tapered/twisted blade was designed to operate on the Combined Experiment Rotor (CER) of the National Renewable Energy Laboratory (NREL), which is a stall-regulated downwind wind turbine having a rated power of 20 kilowatt. The geometry of the new blade set was optimized based on annual energy production subject to the constraints imposed on the design. These constraints were mainly related to scientific needs for fundamental research in rotor aerodynamics. A trade-off study was conducted to determine the effect of the different design constraints. Based on the results of this study, which considered nonlinear twist and taper distributions as well as the NREL S809, S814, S822 and S823 airfoils, a blade having a linear taper and a nonlinear twist distribution that uses the S809 airfoil from root to tip was selected. This blade configuration is the logical continuation of the previous constant-chord twisted and untwisted blade sets and will facilitate comparison with those earlier blades. Despite the design constraints based on scientific needs, the new blade is more representative of commercial blades than the previous blade sets.The new blade was designed to be applicable for three-and two-bladed rotor configurations. To enhance the performance of the new blade in a two-bladed r...
The effects of Gurney flaps were tested on two airfoil sections, the LA203A and the Gottingen 797, in a low speed wind tunnel. Lift and drag forces, wall-pressure distributions and boundarylayer thickness measurements have been carried out,. Different Gurney flap heights ranging from 0.5% to 5.0% chord have been tested in order to identify some optimal configuration of this simple, yet promising device. The results presented are for a chord Reynolds number of 250 000 and reveal, in accordance with higher Reynolds number studies, that Gurney flaps may indeed provide a significant increase in lift a t very little cost in drag. It is further shown that through the proper use of Gurney flaps, the aerodynamic performance of a simple design, easy-t,o-build airfoil can be made practically as good as those of a modern, high performance, complex design. T h e present study suggests that both the critical and the optimal height of Gurney flaps (in t,erms of the l / d ratio) scales with the thickness of the boundary-layer a t the trailing-edge of the baseline airfoil on the pressure side. Based on the results of this study and previous investigations, this conclusion appears supported over a wide range of Reynolds numbers. A preliminary discussion on the physical mechanism behind the Gurney's effects and its scaling is also proposed.
A systematic wind tunnel study was conducted to gain an understanding of the aerodynamic effects of leading‐edge tape, which is typically used on small wind turbines as a protection from blade erosion. The wind tunnel tests included lift and drag measurements over the Reynolds number range from 150,000 to 500,000. In addition, flow visualization experiments were carried out. Various tape configurations were tested on five aerofoils, namely the BW‐3, FX 63‐137, S822, SG6042 and SG6051. Although the magnitude of the aerodynamic effects of the tape was aerofoil‐dependent, it was found that extending the tape beyond 5% chord and staggering multiple tape layers were most beneficial in minimizing the loss in aerofoil performance. The practical significance of the results on wind turbine performance is discussed. In particular, the data for the SG6042 aerofoil were used to quantify the effects of the tape on the power coefficient of small variable‐speed wind turbines. Overall, the different tape configurations tested reduced the power coefficient by no more than 2·1%. From the trends shown, however, larger reductions in power coefficient should be expected for larger wind turbines than those considered, particularly if two layers of tape are used. In light of this study, guidelines for optimum application are suggested. Copyright © 1999 John Wiley & Sons, Ltd.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.