Theoretical Aerodynamic Analyses of Six Airfoils for Use on Small Wind Turbines: July 11, 2002--October 31, 2002

Abstract

The U.S. Department of Energy (DOE), working through its National Renewable Energy Laboratory (NREL), is engaged in a comprehensive research effort to improve the understanding of wind turbine aeroacoustics. Motivation for this effort is the desire to exploit the large expanse of low wind speed sites that tend to be closer to U.S. load centers. Quiet wind turbines are an inducement to widespread deployment, so the goal of NREL's aeroacoustic research is to develop tools for use by U.S. industry in developing and deploying highly efficient, quiet wind turbines at these low wind speed sites. NREL's National Wind Technology Center (NWTC) is implementing a multifaceted approach that includes wind tunnel tests, field tests, and theoretical analyses in direct support of low wind speed turbine development by its industry partners. NWTC researchers are working hand in hand with industry engineers to ensure that research findings are available to support ongoing design decisions. The work described in the present report focuses on the theoretical aerodynamic analysis of airfoils that are candidates for use on small wind turbines. Admittedly, the connection between this aerodynamic work and NREL's aeroacoustic research is somewhat vague. But without a knowledge of both aerodynamic and aeroacoustic performance of airfoils, engineers are frustrated in making decisions on new blade designs. This is particularly true for small wind turbines, which operate at low Reynolds numbers at which airfoil aerodynamic characteristics are both sensitive and difficult to predict. Thus, the present work needs to be considered in the context of the broader research effort on aeroacoustics for small wind turbines. Wind tunnel aerodynamic tests and aeroacoustic tests have been performed on six airfoils that are candidates for use on small wind turbines. Results are documented in the following NREL reports:

Small Wind Turbine Technology

“…Although the same shape of the drag polars was observed in both cases, showing the appearance of the laminar separation bubble, the drag coefficients for a given lift coefficient were found to be higher in the measurements by Selig and McGranahan (2004). Interestingly, a similar discrepancy, limited to the low Reynolds number case of 100,000, was found in a theoretical analysis of small-scale wind turbine airfoils (Somers and Maughmer, 2003), including the Eppler airfoil E387 mentioned above. In their study, the authors use two different airfoil codes, the XFoil and the Eppler Airfoil Design and Analysis Code (Profil00), finding similar results for drag polars, except for the low Reynolds number case of 100,000, where the experimentally observed drag is better reproduced by the Profil00 code.…”

A comprehensive review of the theoretical approaches for the airfoil design of lift-type vertical axis wind turbine

“…2D Navier-Stokes solver (EllipSys2D) and potential Panel method codes (XFOIL, PROFIL [56]) are widely utilized for airfoil analysis before the pre-stall by renowned wind turbine research organizations including NREL [57] and Risoe [58]. Raciti Castelli et al [59] extended the experimental data from Sheldahl and Klimas [49] using the Xfoil.…”

Modeling and optimization of power coefficient using 2^K factorial methodology

“…The blade used in this paper is a tip airfoil (S822) and mainly designed for wind turbines rated between 2-20kW [6]. The values of l C and d C for a Reynold number of 0.7×10 6 is considered in this study and found from the available published data [7].…”