Airfoil characteristics for wind turbines

Abstract Airfoil characteristics for use in the Blade Element Momentum (BEM) methodare derived by use of systematic methods. The characteristics are derived fromdata on Horizontal Axis Wind Turbines (HAWT). The investigation and deri-vation of the airfoil characteristics are based on four different methods: 1) In-verse momentum theory, 2) Actuator disc theory, 3) Numerical optimisationand 4) Quasi-3D CFD computations.The two former methods use as input 3D CFD computations and wind tunnelmeasurements on a 41-m full-scale rotor with LM 19.1 blades. The derived air-foil characteristics show that the maximum lift coefficient at the tip is low andthat the maximum lift coefficient is high at the root compared to 2D airfoilcharacteristics. The use of the derived characteristics in aeroelastic calculationsshows good agreement with measurements for power and flap moments. Fur-thermore, a fatigue analysis shows a reduction in the loads of up to 15 % fromload calculations with the derived airfoil characteristics compared with a com-monly used set of airfoil characteristics.The numerical optimisation is based on both the 3D CFD computations andmeasurements on a 41-m rotor with LM 19.1 and LM 19.0 blades, respectively.The method requires measurements or CFD calculations of power and loadsfrom a turbine and is promising since a set of lift and drag curves is derived thatcan be used to calculate mean values of power and loads. The maximum lift atthe tip is low and at the root it is high compared to 2D airfoil characteristics. Inparticular the power curves were well calculated by use of the optimised airfoilcharacteristics.In the quasi-3D CFD computations, the airfoil characteristics are derived di-rectly. This Navier-Stokes model takes into account rotational and 3D effects.The model enables the study of the rotational effect of a rotor blade at comput-ing costs similar to what is typical for 2D airfoil calculations. The depicted re-sults show that the model is capable of determining the correct qualitative be-haviour for airfoils subject to rotation. The method shows that lift is high at theroot compared to 2D airfoil characteristics.The different systematic methods show the importance of rotational and 3D ef-fects on rotors. Furthermore, the methods show high maximum lift coefficientsat the inboard part of the blade and low maximum lift coefficients at the out-board part of the blade compared to 2D wind tunnel measurements.ISBN 87-550-2415-7ISBN 87-550-2568-4 (internet)ISSN 0106-2840Information Service Department, Riso, 1999

[1]  Dover Publications,et al.  Potential Flow Around a Rotating, Advancing Cylindrical Blade , 1950 .

[2]  Niels N. Sørensen,et al.  General purpose flow solver applied to flow over hills , 1995 .

[3]  C. R. Deboor,et al.  A practical guide to splines , 1978 .

[4]  A. Bruining.  Final report of IEA An- nex XIV : Field Rotor Aero- dynamics , 1997 .

[5]  T. Barth,et al.  A one-equation turbulence transport model for high Reynolds number wall-bounded flows , 1990 .

[6]  S. G. Rubin,et al.  A diagonally dominant second-order accurate implicit scheme , 1974 .

[7]  D. Wilcox.  Turbulence modeling for CFD , 1993 .

[8]  D. Spalding,et al.  A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows , 1972 .

[9]  Jens Nørkær Sørensen,et al.  Three-Level, Viscous-Inviscid Interaction Technique for the Prediction of Separated Flow Past Rotating Wing , 1986 .

[10]  Carl de Boor,et al.  A Practical Guide to Splines , 1978, Applied Mathematical Sciences.

[11]  Mc Croskey.  Measurements of boundary layer transition, separation and streamline direction on rotating blades , 1971 .

[12]  C. Rhie,et al.  A numerical study of the flow past an isolated airfoil with separation , 1981 .

[13]  H. Madsen.  A CFD analysis of the actuator disc flow compared with momentum theory results , 1997 .

[14]  S. F. Radwan,et al.  Boundary-Layer Calculations in the Inverse Mode for Incompressible Flows over Infinite Swept Wings , 1983 .

[15]  Laurence Eugene Fogarty.  The Laminar Boundary Layer on a Rotating Blade , 1951 .

[16]  Helge Aagaard Madsen,et al.  Optimization method for wind turbine rotors , 1999 .

[17]  W. Durand,et al.  Aerodynamic theory : a general review of progress , 1963 .

[18]  Göran Ronsten,et al.  Static pressure measurements on a rotating and a non-rotating 2.375 m wind turbine blade. Comparison with 2D calculations , 1992 .

[19]  J. C. Cooke,et al.  Boundary layers in three dimensions , 1960 .

[20]  F. Menter.  ZONAL TWO EQUATION k-w TURBULENCE MODELS FOR AERODYNAMIC FLOWS , 1993 .

[21]  J. Thirstrup Petersen.  The aeroelastic code HawC - model and comparisons , 1996 .

[22]  I. H. Abbott,et al.  Theory of Wing Sections , 1959 .

[23]  Wen-Zhong Shen,et al.  Numerical method for unsteady 3D Navier-Stokes equations in velocity-vorticity form , 1997 .

[24]  Jens Nørkær Sørensen,et al.  A global Navier-Stokes rotor prediction model , 1997 .

[25]  F. Menter.  Improved two-equation k-omega turbulence models for aerodynamic flows , 1992 .

[26]  F. Menter.  Performance of popular turbulence model for attached and separated adverse pressure gradient flows , 1992 .

[27]  Peter Fuglsang,et al.  Wind Tunnel Tests of the FFA-W3-241, FFA-W3-301 and NACA 63-430 Airfoils , 1998 .

[28]  Tuncer Cebeci,et al.  Calculation of Three-Dimensional Boundary Layers I. Swept Infinite Cylinders and Small Cross Flow , 1974 .

[29]  F. R. Menter.  Performance of popular turbulence models for attached and separated adverse pressure gradient flows , 1991 .