Unsteady Aerodynamics Experiment Phase VI NREL-NASA Ames Wind Tunnel Experiment


The Unsteady Aerodynamics Experiment (UAE) was undertaken to acquire research-grade wind turbine aerodynamics measurements capable of expanding physical comprehension, improving predictive models, and advancing turbine technology and performance. Initiated in 1987 at the National Renewable Energy Laboratory’s (NREL) National Wind Technology Center (NWTC), the UAE evolved through five phases of field experiments during 1987 through 1998.[1-3] Concurrently, analogous wind turbine field experiments aimed at the same objectives were pursued at several laboratories in Europe and Asia.[4,5] Together, these field experiments succeeded in developing procedures and instrumentation for acquiring research-grade measurements in the field test environment and generally confirmed that turbine blades produced flow fields that were highly three-dimensional, strongly separated, and predominantly unsteady.

However, crucial details of the turbine blade flow fields remained obscure, overwhelmed by the temporal and spatial disparities imposed by turbulent atmospheric inflows. To isolate the key blade and rotor fluid mechanics details, atmospheric inflow anomalies needed to be eliminated. Thus, plans were launched simultaneously in the United States and Europe to carry out research-grade turbine aerodynamics experiments in the largest U.S. and EU wind tunnels. Documented and archived in the DAP UAE6 database, the NREL UAE Phase VI experiment was conducted in the National Aeronautics and Space Administration (NASA) 80 ft x 120 ft wind tunnel at the NASA Ames Research Center at Moffett Field, California.[6] The EU Model rotor EXperiment In COntrolled conditions (MEXICO) experiment was carried out in the German-Dutch Wind Tunnels (DNW) Large Low Speed Facility (LLF), located near Marknesse in The Netherlands.[7]

The DAP UAE6 database contains the measurements acquired via experiments in the NASA Ames 80 ft x 120 ft during 2000. The UAE Phase VI wind tunnel experiment objectives were to: 1) acquire research grade aerodynamic and structural measurements 2) on a subscale wind turbine geometrically/dynamically similar to full scale, 3) operating in a controlled, low-turbulence inflow environment.

Primary Contact(s)


The NASA Ames National Full-Scale Aerodynamics Complex (NFAC) encompasses two wind tunnel circuits. The first is a closed loop circuit with a 12.2 m x 24.4 m (40 ft x 80 ft) test section, and the second is an open loop branch with a 24.4 m x 36.6 m (80 ft x 120 ft) test section. The second circuit, containing the 24.4 m x 36.6 m (80 ft x 120 ft) test section, was used for the entire UAE Phase VI experiment. Test section speed in the 80 ft x 120 ft circuit varies continuously from nearly zero to 50 m/s. For operating conditions employed during the UAE Phase VI experiment in the 80 ft x 120 ft test section, flow quality parameters were as follows.

  • Speed non-uniformity across the test section did not exceed +/- 0.25%.
  • Low angularity across the test section was 0.5 degree or less.
  • Centerline turbulence intensity was 0.5% or less.

Addiitonal details regarding the NFAC configuration, operation, and flow quality can be found in Zell [8].

The UAE Phase VI turbine was a 10 m diameter, stall-regulated machine with full-span pitch control that ran at a constant speed of 72 RPM and had a power rating of 20 kW. The rotor had two twisted and tapered blades, which employed the S809 airfoil across the principal portion of the blade radius. Overall, the experiment encompassed 30 different operating states and configurations, summarized in Table 1 in [6]. These included operating and parked rotor states, upwind and downwind rotor modes, rigid and teetered hubs, flat and coned rotors, multiple blade pitch angles, and other configurations. Some of these operating states and configurations were intended to replicate conventional turbine operation, while others aimed to achieve unconventional though physically relevant rotor or blade aerodynamic states. Turbine measurements included blade surface pressures (5 radial stations), blade inflow angle and dynamic pressure (5 radial stations), blade root bending moments, low-speed shaft torque and bending moments, mechanical and electrical power, nacelle yaw moment, blade tip and nacelle accelerations, and positional measurements (e.g., nacelle yaw, rotor azimuth, and blade pitch). In total, 285 data channels, both measured and derived, were acquired from the wind turbine and wind tunnel instrumentation sets. More details regarding UAE Phase VI data are available in [6].


For most Sequences, the UAE6 file naming convention uses eight characters (also explained on pp. 15–16 of [6]). The first letter or number specifies the turbine configuration according to the first column in Table 1 of [6]. The next two digits represent the nominal wind speed in meters per second. The next four digits represent the yaw error angle in degrees. For negative yaw error, M (minus) was used. The last digit indicates the number of data collection repetitions completed at that specific flow condition with zero noting the first repetition. For example, the first time the turbine was positioned at 10° yaw, 7 m/s under test configuration H, the file name is given as H0700100. The first time this test point was repeated, the file name is given as H0700101. Some test sequences used a different file naming convention due to the nature of the test. The file naming conventions for these Sequences are explained on pp. 16–24 in [6].

Across all Sequences, the UAE Phase VI database contains two file types. The first is the *.eng file, which contains the calibrated data parameters in engineering units along with all of the derived parameters. These binary files contain a series of 32-bit floating point real numbers. A 30-second campaign consists of 15,625 records for 285 channels, and each record corresponds to one time step of 1.92 ms. The second file type is the *.hd1 file, which contains summary statistics for the *.eng file. The second line lists the number of channels, the number of records in the corresponding *.eng file, and the time step between records. In subsequent *.hd1 file lines, each channel is represented by one line of text beginning with the channel number. The channel description, units, number of calibration coefficients, offset, slope, mean, maximum, minimum, and standard deviation follow. The last entries are the channel type, location of maximum, location of minimum, and number of frames in which an error occurred.

All files in the UAE Phase VI database are identical with respect to the number of channels they contain, which is 285. All UAE Phase VI *.eng files can be accessed using the MATLAB script, and all *.hd1 files can be opened and read with any common text editor.

Support Files

Use this table to locate Sequences of interest: The Sequence Test Matrix

Descriptions of the individual files and instrumentation for each test sequence can be found in this report: Phase VI Test Report

MATLAB script for extracting data

In these Excel files, select columns to hide channels, and select the top row to use Data - Filters

Wind Tunnel Load Statistics (Excel)

Wind Tunnel Pressure Tap Statistics (Excel)

Further Information

Machine Information and Diagrams (PDF)


  1. Butterfield, C., W. Musial, and D. Simms, “Combined Experiment Phase I Final Report,” NREL/TP-257-4655, National Renewable Energy Laboratory, Golden, CO, October 1992.
  2. Simms, D., M. Hand, L. Fingersh, and D. Jager, “Unsteady Aerodynamics Experiment Phases II-IV Test Configurations and Available Data Campaigns,” NREL/TP-500-25950, National Renewable Energy Laboratory, Golden, CO, July 1999.
  3. Hand, M., D. Simms, L. Fingersh, D. Jager, and J. Cotrell, “Unsteady Aerodynamics Experiment Phases V: Test Configuration and Available Data Campaigns,” NREL/TP-500-29491, National Renewable Energy Laboratory, Golden, CO, August 2001.
  4. Schepers, J. G., A. Brand, A. Bruining, J. M. R. Graham, M. Hand, D. Infield, H. A. Madsen, R. J. H. Paynter, and D. Simms, “Final Report of IEA Annex XIV: Field Rotor Aerodynamics,” ECN-C--97-027, Energy Research Center of the Netherlands, Petten, The Netherlands, June 1997.
  5. Schepers, J. G., A. Brand, A. Bruining, J. M. R. Graham, M. Hand, D. Infield, H. A. Madsen, T. Maeda,J. H. Paynter, R. van Rooij, Y. Shimizu, D. Simms, and N. Stefanatos, “Final Report of IEA Annex XVIII: Enhanced Field Rotor Aerodynamics Database,” ECN-C--02-016, Energy Research Center of the Netherlands, Petten, The Netherlands, February 2002.
  6. Hand, M., D. Simms, L. Fingersh, D. Jager, J. Cotrell, S. Schreck, and S. Larwood, “Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Configurations and Available Data Campaigns,” NREL/TP-500-29955, National Renewable Energy Laboratory, Golden, CO, December 2001.
  7. Boorsma, K., and J. G. Schepers, “Description of experimental setup MEXICO measurements,” ECN-X--11-120, Energy Research Center of the Netherlands, Petten, The Netherlands, October 2011.
  8. Zell, P., “Performance and Test Section Flow Characteristics of the National Full-Scale Aerodynamics Complex 80- by 120-Foot Wind Tunnel,” NASA-TM-103920, January 1993.
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