Facility for Calibrating Anemometers as a Function of Air Velocity Vector and Turbulence

NIST calibrates anemometers as a function of airspeed vector and turbulence intensity (Tu). The vector capability (sometimes called "3-D") is particularly important for calibrating multi-hole differential-pressure probes that are often used to quantify pollution emitted by smokestacks of coal-burning electric power plants. Starting with a conventional "1-D" wind tunnel, we achieved vector and Tu capabilities by installing translation/rotation stages and removable turbulence generators (grids or flags). The calibration ranges are: yaw angle ±180°; pitch angle ±45°; airspeed 1 m/s to 30 m/s; turbulence intensity 0.07 ≤ Tu ≤ 0.25; average data collection rate: 300 points/hour at fixed Tu. The system's expanded uncertainties corresponding to 95 % confidence level are: airspeed 0.0045×|V|+(0.036/|V|)² where |V| is the magnitude of the airspeed in m/s; pitch and yaw angles 0.3°; and turbulence intensity 0.03 Tu. The airspeed working standard is a Laser Doppler Anemometer that is traced to SI unit of velocity via a spinning disk. Calibrations are corrected for blockage by the instrument under test and its supports.