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The computation of the aerodynamic performance, flow separation, and dynamic stall on a rotating wing or blade continues to challenge the rotorcraft designer. Compressibility, stall delay, rapid change of angle of attack, dynamic stall, wake interaction, and flow unsteadiness are problems unique to rotors. Extensive research and testing to improve the calculations have been conducted over the years to help solve these problems as they relate to rotorcraft. This past year a partnership was initiated between the National Renewable Energy Laboratory and Ames to apply computational fluid dynamics (CFD) and comprehensive computation tools developed for rotorcraft to the study of wind turbines.
CFD performance calculations (see fig. 1) were made of a research horizontal-axis wind turbine (HAWT) using a compressible Reynolds-averaged Navier-Stokes equations code using overset grids (OVERFLOW code version 1.6ap-rotorcraft) and a comprehensive vortex lattice method code (CAMRAD II). The results were compared with measurements collected during a full-scale wind tunnel test of the research wind turbine in the NASA Ames Full-Scale Aerodynamic Complex (80- by 120-Foot Wind Tunnel) (Fig. 2).
The research wind turbine was 10 meters (m) in diameter, turned at 72 revolutions per minute (rpm), and could generate 20 kilowatts (kW) of power. The turbine was highly instrumented with over 150 pressure transducers, strain gages, and motion sensors to identify its operational state. Easily reconfigured with both blade-pitch and nacelle azimuth control, the research wind turbine was tested in many different operational variations. Nominal testing was at airspeeds between 5 and 25 meters per second (m/sec) with a few test points recorded at 40 m/sec.
Point of Contact R. Kufeld
(650) 604-5664
rkufeld@mail.arc.nasa.gov
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Fig. 1. Velocity contours for the complete rotor-tower-nacelle configuration as calculated by OVERFLOW.
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Fig. 2. The research wind turbine inside the 80- by 120-Foot Wind Tunnel expelling smoke for wake visualization; airspeed = 7 m/sec, blade pitch = 3 degrees, yaw angle = 0.0 degrees.
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