The high air speed standard based on primary standard of gas flowrate

The air speed measurement is important as the quantitative index for the assessment of the building wind-resistance, the indoor thermal environment and the aerodynamic characteristic of high speed vehicles. NMIJ has established the high air speed standard facility and started a calibration service for Pitot-static tubes. This facility covers the air speed range from 40 m/s up to 90 m/s with relative expanded uncertainty (k = 2) of 0.63 %. The reference air speed is derived from the national primary gas flowrate standard. The test section for conversion from flowrate to air speed is installed at the test line of the closed loop gas flowrate calibration facility. The standard air speed at the center of the nozzle exit is obtained by comparing the integral value of the air speed profile and the standard gas flowrate. Against this standard air speed, a dedicated wind tunnel, which serves for daily calibration service, is calibrated by using a total pressure tube as a transfer standard. An internal comparison was carried out between the new wind tunnel and the conventional medium-speed wind tunnel. The comparison result agreed well enough to validate the capability of the new wind tunnel. This paper describes the calibration system, the traceability chain and the uncertainty analysis of the new air speed standard.