The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform

James L Tangler - One of the best experts on this subject based on the ideXlab platform.

  • Wind tunnel tests of two airfoils for wind turbines operating at high reynolds numbers
    2000 ASME Wind Energy Symposium, 2000
    Co-Authors: Dan M. Sommers, James L Tangler
    Abstract:

    The objectives of this study were to verify the predictions of the Eppler Airfoil Design and Analysis Code for Reynolds numbers up to 6 x 106 and to acquire the section characteristics of two airfoils being considered for large, megawatt-size wind turbines. One airfoil, the S825, was designed to achieve a high Maximum Lift Coefficient suitable for variable-speed machines. The other airfoil, the S827, was designed to achieve a low Maximum Lift Coefficient suitable for stall-regulated machines. Both airfoils were tested in the NASA Langley Low-Turbulence Pressure Tunnel (LTPT) for smooth, fixed-transition, and rough surface conditions at Reynolds numbers of 1, 2, 3, 4, and 6 x 106. The results show the Maximum Lift Coefficient of both airfoils is substantially underpredicted for Reynolds numbers over 3 x 106 and emphasized the difficulty of designing low-Lift airfoils for high Reynolds numbers.

  • Blade design trade-offs using low-Lift airfoils for stall-regulated HAWTs
    Journal of Solar Energy Engineering, 1999
    Co-Authors: Philippe Giguere, Michael S. Selig, James L Tangler
    Abstract:

    A systematic blade design study was conducted to explore the trade-offs in using low-Lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a Maximum-Lift Coefficient ranging from 0.7-1.2 were considered in this study, with the main objective of identifying the practical lower limit for the Maximum-Lift Coefficient. Blades were optimized for both Maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that the effect of the Maximum-Lift Coefficient on the cost of energy is small with a slight advantage to the highest Maximum Lift Coefficient case considered in this study. As a consequence, higher Maximum Lift Coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, provided the airfoils yield acceptable stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

  • blade design trade offs using low Lift airfoils for stall regulated hawts
    Journal of Solar Energy Engineering-transactions of The Asme, 1999
    Co-Authors: Philippe Giguere, Michael S. Selig, James L Tangler
    Abstract:

    A systematic blade design study was conducted to explore the trade-offs in using low-Lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a Maximum Lift Coefficient ranging from 0.7-1.2 were considered in this study, with the main objective of identifying the practical lower limit for the Maximum Lift Coefficient. Blades were optimized for both Maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that reducing the Maximum Lift Coefficient below the upper limit considered in this study increases the cost of energy independently of the wind regime. As a consequence, higher Maximum Lift Coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, as long as they provide gentle stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

  • Wind tunnel test of the S814 thick root airfoil
    Journal of Solar Energy Engineering, 1996
    Co-Authors: D.m. Somers, James L Tangler
    Abstract:

    The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high Maximum Lift Coefficient designed to be largely insensitive to leading-edge roughness effects. The 24 percent thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s Maximum Lift-to-drag ratio was designed to occur at a high Lift Coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds number of 1.5 {times} 10{sup 6}, the Maximum Lift Coefficient with transition free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted Maximum Lift Coefficient of almost 1.6. With transition fixed at the leading edge, the Maximum Lift Coefficient is 1.22. The small difference in Maximum Lift Coefficient between the transition-freemore » and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low Maximum-Lift-Coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.« less

  • NREL airfoil families for HAWTs
    1995
    Co-Authors: James L Tangler, Dan M Somers
    Abstract:

    The development of special-purpose airfoils for horizontal-axis wind turbines (HAWTs) began in 1984 as a joint effort between the National Renewable Energy Laboratory (NREL), formerly the Solar Energy Research Institute (SERI), and Airfoils, Incorporated. Since that time seven airfoil families have been designed for various size rotors using the Eppler Airfoil Design and Analysis Code. A general performance requirement of the new airfoil families is that they exhibit a Maximum Lift Coefficient (c{sub l,max}) which is relatively insensitive to roughness effects. The airfoil families address the needs of stall-regulated, variable-pitch, and variable-rpm wind turbines. For stall-regulated rotors, better peak-power control is achieved through the design of tip airfoils that restrain the Maximum Lift Coefficient. Restrained Maximum Lift Coefficient allows the use of more swept disc area for a given generator size. Also, for stall-regulated rotors, tip airfoils with high thickness are used to accommodate overspeed control devices. For variable-pitch and variable-rpm rotors, tip airfoils having a high Maximum Lift Coefficient lend themselves to lightweight blades with low solidity. Tip airfoils having low thickness result in less drag for blades having full-span pitch control. Annual energy improvements from the NREL airfoil families are projected to be 23% to 35% for stall-regulatedmore » turbines, 8% to 20% for variable-pitch turbines, and 8% to 10% for variable-rpm turbines. The improvement for stall-regulated turbines has been verified in field tests.« less

W A Timmer - One of the best experts on this subject based on the ideXlab platform.

  • an overview of naca 6 digit airfoil series characteristics with reference to airfoils for large wind turbine blades
    47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 5-8 January 2009 Orlando Florida; AIAA 2009-268, 2009
    Co-Authors: W A Timmer
    Abstract:

    This paper investigates the NACA 63 and 64 6-digit series of airfoils tested in the NACA LTPT in view to verify the RFOIL calculated airfoil characteristics for high Reynolds numbers. Some anomalies in the zero-Lift angles of 15% and 18% thick airfoils from these series are identified, both in the airfoil clean case and in case of wrap-around roughness. It is found that RFOIL predicts the Maximum Lift Coefficient at a Reynolds number of 3 million well, but consistently under predicts the Cl,max for Reynolds numbers of 6 and 9 million. It is, however, based on other comparisons at high Reynolds numbers unclear if this is due to an inability of the prediction code or to a deviation in the test results. The drag Coefficient is under predicted with about 9% for a wide range of airfoils and Reynolds numbers. Due to wrap-around roughness the Maximum Lift Coefficient decreases with 18% to 20%.

  • the effect of roughness at high reynolds numbers on the performance of aerofoil du 97 w 300mod
    Wind Energy, 2004
    Co-Authors: W A Timmer, Alois Peter Schaffarczyk
    Abstract:

    This paper discusses the results of wind tunnel measurements performed on a modified DU 97-W300 airfoil at Reynolds numbers between 1x10 and 10x10 in the cryogenic wind tunnel of the DNW at Cologne, Germany. The airfoil was modified by reducing the trailing edge thickness from 1.74% to 0.49%. Although the measurements showed large scatter when flow separation occurred on the model it was possible to establish the variation with Reynolds number of the Maximum Lift Coefficient, the Maximum Lift-drag ratio and the design-Lift Coefficient for a Mach number of 0.2. Furthermore the effect of wrap-around Carborundum roughness and zigzag tape of 0.4 mm thickness at upper and lower surface was studied. The experimental results were compared with RFOIL calculations. The measurements indicate that there was no significant variation in the Maximum Lift Coefficient with Reynolds number for the clean airfoil. In contrast to the RFOIL calculations the experimental Maximum Lift-drag ratio decreased with Reynolds number from an average of 95 at R=3x10 to about 85 at R=10x10. The Carborundum 60 roughness had a larger negative effect on the airfoil performance than the zigzag tape, but in both cases the airfoil performance improved drastically with increasing Reynolds number.

Alois Peter Schaffarczyk - One of the best experts on this subject based on the ideXlab platform.

  • the effect of roughness at high reynolds numbers on the performance of aerofoil du 97 w 300mod
    Wind Energy, 2004
    Co-Authors: W A Timmer, Alois Peter Schaffarczyk
    Abstract:

    This paper discusses the results of wind tunnel measurements performed on a modified DU 97-W300 airfoil at Reynolds numbers between 1x10 and 10x10 in the cryogenic wind tunnel of the DNW at Cologne, Germany. The airfoil was modified by reducing the trailing edge thickness from 1.74% to 0.49%. Although the measurements showed large scatter when flow separation occurred on the model it was possible to establish the variation with Reynolds number of the Maximum Lift Coefficient, the Maximum Lift-drag ratio and the design-Lift Coefficient for a Mach number of 0.2. Furthermore the effect of wrap-around Carborundum roughness and zigzag tape of 0.4 mm thickness at upper and lower surface was studied. The experimental results were compared with RFOIL calculations. The measurements indicate that there was no significant variation in the Maximum Lift Coefficient with Reynolds number for the clean airfoil. In contrast to the RFOIL calculations the experimental Maximum Lift-drag ratio decreased with Reynolds number from an average of 95 at R=3x10 to about 85 at R=10x10. The Carborundum 60 roughness had a larger negative effect on the airfoil performance than the zigzag tape, but in both cases the airfoil performance improved drastically with increasing Reynolds number.

D.m. Somers - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Flap Deflection on Section Characteristics of S813 Airfoil; Period of Performance: 1993--1994
    2005
    Co-Authors: D.m. Somers
    Abstract:

    The effect of small deflections of a 30% chord, simple flap on the section characteristics of a tip airfoil, the S813, designed for 20- to 30-meter, stall-regulated, horizontal-axis wind turbines has been evaluated theoretically. The decrease in Maximum Lift Coefficient due to leading-edge roughness increases in magnitude with increasing, positive flap deflection and with decreasing Reynolds number.

  • Effects of Airfoil Thickness and Maximum Lift Coefficient on Roughness Sensitivity: 1997--1998
    2005
    Co-Authors: D.m. Somers
    Abstract:

    A matrix of airfoils has been developed to determine the effects of airfoil thickness and the Maximum Lift to leading-edge roughness. The matrix consists of three natural-laminar-flow airfoils, the S901, S902, and S903, for wind turbine applications. The airfoils have been designed and analyzed theoretically and verified experimentally in the Pennsylvania State University low-speed, low-turbulence wind tunnel. The effect of roughness on the Maximum life increases with increasing airfoil thickness and decreases slightly with increasing Maximum Lift. Comparisons of the theoretical and experimental results generally show good agreement.

  • Wind tunnel test of the S814 thick root airfoil
    Journal of Solar Energy Engineering, 1996
    Co-Authors: D.m. Somers, James L Tangler
    Abstract:

    The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high Maximum Lift Coefficient designed to be largely insensitive to leading-edge roughness effects. The 24 percent thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s Maximum Lift-to-drag ratio was designed to occur at a high Lift Coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds number of 1.5 {times} 10{sup 6}, the Maximum Lift Coefficient with transition free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted Maximum Lift Coefficient of almost 1.6. With transition fixed at the leading edge, the Maximum Lift Coefficient is 1.22. The small difference in Maximum Lift Coefficient between the transition-freemore » and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low Maximum-Lift-Coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.« less

Nicholas Alley - One of the best experts on this subject based on the ideXlab platform.

  • Predicting Maximum Lift Coefficient for twisted wings using Lifting-line theory
    Journal of Aircraft, 2007
    Co-Authors: Warren F. Phillips, Nicholas Alley
    Abstract:

    A method is presented that allows one to predict the Maximum Lift Coefficient for a wing from knowledge of wing geometry and Maximum airfoil section Lift Coefficient. The method applies to wings of arbitrary planform and includes the effects of twist and sweep. In addition to predicting the section Lift distribution for a wing of known planform with a known twist distribution, the method can be used to predict the twist distribution, which will produce any desired section Lift distribution along the span of an unswept wing of any given planform. The method is shown to predict the twist distribution required to minimize induced drag and is also used to predict the twist distribution that maximizes the wing Lift Coefficient, while keeping the total amount of required twist at a practical level.

  • Predicting Maximum Lift Coefficient for Twisted Wings Using Computational Fluid Dynamics
    Journal of Aircraft, 2007
    Co-Authors: Nicholas Alley, Warren F. Phillips, Robert E. Spall
    Abstract:

    *† ‡ A method is presented that allows one to predict the Maximum Lift Coefficient for a finite wing from knowledge of wing geometry and Maximum airfoil section Lift Coefficient. This approach applies to wings of arbitrary planform and includes the effects of twist and sweep. The method utilizes a correlation obtained from grid-resolved computational fluid dynamics solutions for 25 different wing geometries. These wings had aspect ratios ranging from 4 to 20, taper ratios from 0.5 to 1.0, quarter-chord sweep angles from 0 to 30 degrees, and linear geometric washout ranging from 0 to 8 degrees. For this range of parameters, the ratio of Maximum wing Lift Coefficient to Maximum airfoil section Lift Coefficient varied from about 0.70 to 0.98, with high-aspect-ratio tapered wings producing the highest values and lowaspect-ratio wings with washout and sweep producing the lowest values.