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Wind profile measurements at the Mod-1 site at Boone, North Carolina

OSTI ID: 5281353 - Three components of the wind field, temperature and pressure were measured by means of tethered balloon-borne sondes from the surface to 175 m (577 ft) and by means of a nacelle mounted system, from the surface to hub height of 43 m (140 ft). Measurements were taken over a ten day period at the Mod-1 Site in Boone, NC. Composite wind profiles are presented for different flow and stability regimes. The most extreme shears, on the order of .3 s/sup -1/, were found between 10 m (33 ft) and hub height. Individual profiles of wind and temperature show the effect of nocturnal cooling and accompanying surface stratification on the intensity of thw wind shear. Gustiness measured in terms of departures of one and two standard deviations above and below the mean, occurs at all heights across the rotor of the Mod-1 machine. Most frequent gustiness, however, occurs at and below hub height with periods up to 8 secs. Similar fluctuations are observed in the vertical component of the velocity field and in the direction of the horizontal wind. The depth of the shearing layer is critically related to hub height and rotor radius. The depth of the shearing layer appears to vary most significantly with thermal stratification; strong surface inversions producing shallow intense shearing layers; adiabatic conditions reflecting only topographically induced shear. For a given site and a given generator, hub height should be guided by the depth of the mean shear layer under adiabatic conditions plus the radius of the rotor."

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