Support Engineers' Tool Kit

Reports - Wind Turbines


This page contains reports with useful information about a series of topics relevant to the structural engineer working with Wind Turbines. Beside the reports listed here, a link to the SANDIA NATIONAL LABORATORIES will redirect you to more than 100 reports on wind turbine technology.



Extensive colection of online (downloadable) abstracts and reports of the Sandia National Laboratories, covering materials (metallic and composite), fatige, loads, flutter and aeroelasticity, adaptive controls, noise, aerodynamics, bonded joints, tests, reliability, etc. 


Risø-R-1393(EN) (2,137 Kb) 

Compression Strength of a Fibre Composite Main Spar in a Wind Turbine Blade

Find Mølholt Jensen


In this report the strength of a wind turbine blade is found and compared with a full-scale test, made in the same project. Especially the postbuckling behaviour of the compression flange is studied. Different compressive failure mechanisms are discussed and the limitations in using the Finite Element Method. A suggestion to the further work is made.

SAND99-0089  (8,860 KB) 

On the Fatigue Analysis of Wind Turbines

Herbert J. Sutherland


Modern wind turbines are fatigue critical machines that are typically used to produce electrical power from the wind. Operational experiences with these large rotating machines indicated that their components (primarily blades and blade joints) were failing at unexpectedly high rates, which led the wind turbine community to develop fatigue analysis capabilities for wind turbines. Our ability to analyze the fatigue behavior of wind turbine components has matured to the point that the prediction of service lifetime is becoming an essential part of the design process. In this review paper, I summarize the technology and describe the “best practices” for the fatigue analysis of a wind turbine component. The paper focuses on U. S. technology, but cites European references that provide important insights into the fatigue analysis of wind turbines.

NREL/TP-500-34478  (735 KB) 

Semi-Empirical Aeroacoustic Noise Prediction Code for Wind Turbines

P. Moriarty and P. Migliore 


A series of semi-empirical aeroacoustic noise prediction subroutines was written and incorporated into the National Renewable Energy Laboratory’s (NREL's) aeroelastic simulation code: FAST [1]. The subroutines predict six different forms of aerodynamically produced noise that were superimposed to calculate the total aeroacoustic signature of an operating wind turbine. The outputs of the code are sound pressure level spectra of these various sources in one-third octave bands. Parts of the code were validated against acoustic data from two-dimensional airfoil tests. Results from these validation studies were somewhat mixed. For certain wind tunnel conditions, the code predicted sound pressure levels within 2 decibels (dB) of the data, while for others the difference between prediction and data was 6 dB or more. Trends and relative amplitude changes in the predictions often mimicked those seen in the data. Predictions of the NACA 0012 airfoil were more accurate than those of the other airfoils. The code was also validated against measurements from a test of a full-scale wind turbine, the Atlantic Orient Corporation (AOC) 15/50. The noise predictions of this turbine were dominated by ...

Risø-R-1188(EN)  (2,809 KB) 

Turbulence and turbulence-generated structural loading in wind turbine clusters

Sten Tronæs Frandsen


Turbulence – in terms of standard deviation of wind speed fluctuations – and other flow characteristics are different in the interior of wind farms relative to the free flow and action must be taken to ensure sufficient structural sustainability of the wind turbines exposed to “wind farm flow”. The standard deviation of wind speed fluctuations is a known key parameter for both extreme- and fatigue loading, and it is argued and found to be justified that a model for change in turbulence intensity alone may account for increased fatigue loading in wind farms. Changes in scale of turbulence and horizontal flow-shear also influence the dynamic response and thus fatigue loading. However, these parameters are typically – negatively or positively – correlated with the standard deviation of wind speed fluctuations, which therefore can, if need be, represent these other variables. Thus, models for spatially averaged turbulence intensity inside the wind farm and direct-wake turbulence intensity are being devised and a method to combine the different load situations ...
Also, extreme loading under normal operation for wake conditions and the efficiency of very large wind farms are discussed.

Risø–R–1437(EN)  (7,025 KB) 

Wind Simulation for Extreme and Fatigue Loads

M. Nielsen, G. C. Larsen, J.Mann, S. Ott, K. S. Hansen and B. J. Pedersen

Document in English but no abstract or summary available in English.

NREL/CP-500-36900  (699 KB) 

Wind Turbine Post-Stall Airfoil Performance Characteristics Guidelines for Blade-Element Momentum Methods

J. Tangler and J. David Kocurek


The objective of this study was to provide post-stall airfoil data input guidelines for the prediction of peak and post-peak rotor power when using blade-element momentum theory. A steady-state data set from the Unsteady Aerodynamic Experiment (UAE) rotor test was used to provide guidelines for the development of a global post-stall method for the prediction of post-stall 3-D airfoil characteristics to be used with 2-D airfoil data. Based on these UAE data, methods to emulate the 3-D aerodynamics in the post-stall region were explored. Also suggested are experimental tests needed to better understand the 3-D flow physics and to quantify needed theory or empirical factors for a global post-stall approach to support blade-element momentum methods.

Wind Turbine Noise Issues  (732 KB) 

Anthony L. Rogers and James F. Manwell


Wind turbines generate noise from multiple mechanical and aerodynamic sources. As the technology has advanced, wind turbines have gotten much quieter, but noise from wind turbines is still a public concern. The problems associated with wind turbine noise have been one of the more studied environmental impact areas in wind energy engineering. Noise levels can be measured, but, similar to other environmental concerns, the public's perception of the noise impact of wind turbines is in part a subjective determination. Noise is defined as any unwanted sound. Concerns about noise….

NREL/SR-500-32495  (1,518 KB) 

WindPACT Turbine Rotor Design Study


This report presents the results of a study completed by Global Energy Concepts (GEC) as part of the U.S. Department of Energy’s (DOE’s) WindPACT (Wind Partnership for Advanced Component Technologies) project. The purpose of the WindPACT project is to identify technology improvements that will enable the cost of energy (COE) from wind turbines to fall to a target of 3.0¢/kWh in low-wind speed sites. Other parts of the project have examined blade scaling, logistics, balance-of-station costs, and drivetrain design, while this project was concerned with the effect of different rotor configurations and the effect of scale on those rotors.

NREL/TP-500-35328  (1,981 KB) 

Structural Dynamics Verification of Rotorcraft Comprehensive Analysis System (RCAS)


National Renewable Energy Laboratory (NREL), and the National Wind Technology Center (NWTC) for predicting the dynamic response, loads, and fatigue life of wind turbines. FAST (Fatigue, Aerodynamics, Structures, and Turbulence) [6] is a wind-turbine-specific structural dynamic code originally developed by Oregon State University and the University of Utah and later extensively upgraded by NWTC researchers [7]. ADAMS [8-9], or Automated Dynamic Analysis of Mechanical Systems, is a commercial, general-purpose, dynamics code available from the MSC.Software Corporation that is capable of modeling wind turbines using a multi-rigid-body approach. Both FAST and ADAMS are usually coupled with the University of Utah’s AeroDyn aerodynamics package [10] to allow aeroelastic simulations. Unfortunately, these codes do not offer some key capabilities required for a more comprehensive analysis and design of large, flexible wind turbines using multivariable… 

Risø-R-1492(EN) (3,010 KB) 

KNOW-BLADE Task-4 report; Navier-Stokes Aeroelasticity

E.S. Politis, I.G. Nikolaou, P.K. Chaviaropoulos,F. Bertagnolio, N.N. Sørensen and J. Johansen


The problem of the aeroelastic stability of wind turbine blades is addressed in this report by advancing the aerodynamic modelling in the beam element type codes from the engineering-type empirical models to unsteady, 2D or 3D, Navier-Stokes solvers. In this project, structural models for the full wind turbine blade have been combined with 2D and 3D unsteady Navier-Stokes solvers. The relative disadvantage of the quasi-3D approach (where the elastic solver is coupled with a 2D Navier-Stokes solver) is its inability to model induced flow. The lack of a validation test case did not allow for quantitative comparisons with experimental data to be carried out; instead the results of the advanced aeroelastic tools are qualitatively cross-compared. All investigated methods predicted qualitatively similar results. They all resulted in positive aerodynamic damping values for the flap mode, in a decrease in damping with the increase of wind speeds and in a minimum value…

NREL/SR-500-35339 (3,986 Kb) 

Wind Tunnel Aeroacoustic Tests of Six Airfoils for Use onSmall Wind Turbines

Stefan Oerlemans 


Aeroacoustic wind tunnel tests were performed of six airfoils that are candidates for use on small  wind turbines. The acoustic measurements were done in NLR's Small Anechoic Wind Tunnel, fora range of wind speeds (U) and angles of attack, with and without boundary layer tripping. Besides the airfoil self noise measurements in a clean tunnel flow, the models were also tested with a turbulence grid in the nozzle,to investigate airfoil noise associated with inflow turbulence.  A 48-microphone out-of-flow acoustic array was used to locate noise sources and to separate airfoil noise…

AIAA-2004-1185 (700 Kb) 


P. Migliore, J. van Dam and A. Huskey


Eight small wind turbines ranging from 400 watts to 100 kW in rated power were tested for acoustic emis-sions at the U.S. Department of Energy’s National Re-newable Energy Laboratory. Rigorous test procedures based on international standards were followed for measurements and data analyses. Results are presented in the form of sound pressure level versus wind speed, where the sound was recorded downwind of the turbine at a distance equal to the hub height plus half the rotor diameter. When there was sufficient separation be-tween wind turbine noise and background noise, the apparent sound power level was calculated. In several cases, this was not possible. The implications of this problem are discussed briefly. Some of the configura-tions tested were specifically developed to reduce the noise level of their predecessors. Test data for these machines demonstrate marked progress toward quieter turbines.

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