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 ( ). 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 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 ≤ ≤ 0.25; average data collection rate: 300 points/hour at fixed . The system's expanded uncertainties corresponding to 95 % confidence level are: airspeed 0.0045×| |+(0.036/| |) where | | is the magnitude of the airspeed in m/s; pitch and yaw angles 0.3°; and turbulence intensity 0.03 . The airspeed working standard is a Laser Doppler Anemometer that is traced to SI unit of velocity a spinning disk. Calibrations are corrected for blockage by the instrument under test and its supports.