An analysis was performed to determine the risk posed by wind turbine fragments on roads and buildings at the National Wind Technology Center at the National Renewable Energy Laboratory. The authors used a previously developed model of fragment trajectory and took into account the wind speed/direction distribution at the site and the probability of rotor failure. The site-specific risk was assessed by determining the likelihood of impact and related consequences. For both the roads and buildings, the risk varied from low to routine, which was considered acceptable.

This report describes the work performed within the IEA Annex XIV 'Field Rotor Aerodynamics' and its successor IEA Annex XVIII 'Enhanced Field Rotor Aerodynamics Database'. In these Annexes 7 organisations from 6 different countries collaborated in performing aerodynamic experimental programs on full scale horizontal axis wind turbines at field conditions. In such experimental programs local aerodynamic quantities (forces, velocities) are measured at several locations along a rotor blade. As a result of the international collaboration within the IEA Annexes it has been possible to coordinate data processing and to crate and maintain a database of measured data from all participants in a common file format. The database is stored on CD-ROM or accessible through Internet. In principle the database is available for outside parties. The detailed aerodynamic measurements obtained on very different turbines, give a unique opportunity to better understand the aerodynamic behaviour of a wind turbine. This may result in the development and validation of more accurate aerodynamic models.

The primary objective of the insteady aerodynamics experiment was to provide information needed to quantify the full-scale, three-dimensional aerodynamic behavior of horizontal-axis wind turbines. This report is intended to familiarize the user with the entire scope of the wind tunnel test and to support the use of the resulting data.

Data from the National Renewable Energy Laboratory`s Combined Experiment has been utilized to develop techniques for indirectly calculating the instantaneous local dynamic pressure and angle of attack on a horizontal axis wind turbine. First, an analytic model based upon inflow geometry relative to the wind turbine was developed for both parameters. Second, dynamic pressure and angle of attack were inferred from the pressure required to normalize the blade stagnation point to C{sub p} = 1.0. Third, rotor blade pressure profiles were compared to those from wind tunnel tests to determine angle of attack. Test results are shown over a variety of typical inflow conditions and are corroborated by measured data. Differences between the calculated and measured values are also discussed.

The United States Department of Energy and the National Renewable Energy Laboratory (NREL) are conducting research to improve a wind turbine technology. One program, the Combined Experiment, has focused on making measurements needed to understand aerodynamic and structural responses of horizontal-axis wind turbines (HAWT). A new phase of this program, the Unsteady Aerodynamics Experiment, will focus on quantifying unsteady aerodynamic phenomena prevalent install controlled HAWTs. Optimally twisted blades and innovative data acquisition systems will be used in these tests. data can now be acquired and viewed interactively during turbine operations. This paper describes the Unsteady Aerodynamics Experiment and highlights planned future research activities.

Combined Experiment, has focused on making measurements needed to understand aerodynamic and structural responses of horizontal-axis wind turbines (HA WT).A new phase of this program, the Unsteady Aerodynamics Experiment, will focus on quantifying unsteady aerodynamic phenomena prevalent in stall-controlled HA WTs.Optimally twisted blades and innovative instrumentation and data acquisition systems will be used in these tests.Data can now be acquired and viewed interactively during turbine operations.This paper describes the NREL Unsteady Aerodynamics Experiment and highlights planned future research activities.

The National Renewable Energy Laboratory (NREL) has teamed up with Zond Systems, Inc., to provide a rugged, low-cost, advanced data-acquisition system (ADAS) for use in field test projects. The ADAS simplifies the process of making accurate measurements on mechanical equipment exposed to harsh environments. It provides synchronized, time-series measurement data from multiple, independent sources. The ADAS is currently being used to acquire data from large wind turbines in operational wind-plant environments. ADAS modules are mounted on rotating blades, turbine towers, nacelles, control modules, meteorological towers, and electrical stations. The ADAS has the potential to meet the testing and monitoring needs of many other technologies as well, including vehicles, heavy equipment, piping and power transmission networks, and building energy systems.