Outdoor air flows and flue-gas flows in large conduits and large stacks have significant swirl and turbulence. Accurate measurements of such complex flows are needed by weather services and diverse industries (e.g. automotive, aircraft, wind-power, fossil-fueled electricity-generating). The instruments used for accurately measuring complex flows must be calibrated under conditions similar to the conditions encountered when these instruments are used in the field. To meet this requirement, NIST developed a 3-dimensional (3-D) calibration rig that orients test instruments at user-selected pitch angles (-45 degree to 45 degree) and yaw angles (-180 degree to +180 degree) with a resolution of 0.1 degree with respect to the air flow in NISTs wind tunnel. The rig accommodates probes up to 2.5 m long and achieves an expanded air speed uncertainty of approximately 1% (95 % confidence level) over the range 5 m/s to 45 m/s. For measurements in turbulence intensities up to 20 %, we install turbulence-generating flow conditioners in the wind tunnel. We tested four methods of measuring turbulence intensity: (1), laser doppler anemometer, (2) high-frequency, 3-D multi-hole, pressure probe, (3) constant-temperature hot-wire anemometer, and (4) L-shaped pitot tube. Methods (1), (2), and (3) were in mutual agreement. This agreement implies that NISTs new rig can measure the response of virtually any anemometer or probe to a well-defined airspeed vector at diverse turbulence levels. The data from the L-shaped pitot tube [Method (4)] must be corrected for the response time of the differential pressure gauge and for flow in the tubes connecting the pitot tube to the pressure gauge. We illustrate NISTs new capabilities by displaying turbulence-dependent calibrations of an L-shaped pitot tube, a conical pressure probe (mutli-hole, 3-D pitot tube), and an S-probe (a two-port pressure probe that is widely used to measure flue gas flows in the stacks of power plants).
April 13-17, 2015
9th International Symposium on Fluid Flow Measurement (ISFFM)
airspeed calibration, wind tunnel, flow measurement, pitot static tube, multi-hole static probe, hot-wire anemometer, turbulence intensity, turbulence generators