Bilateral Airspeed Comparison (2–20 m/s) Using Three Transfer Standards

Published

May 20, 2026

Author(s)

Christopher Crowley, Iosif Shinder, Joey Boyd, Fábio Costa, Samuel Araújo

Abstract

A bilateral comparison of airspeed standards between NIST and Inmetro was carried out over the range 2 m/s to 20 m/s using three transfer standards: a Pitot tube, a 3D ultrasonic anemometer, and a laser Doppler anemometer (LDA). The instruments were calibrated both in wind tunnels and against a spinning-disk system that provides a direct mechanical realization of airspeed. NIST performed the measurements in a 1.5 m × 2.1 m closed-return wind tunnel and with an optical-chopper spinning disk, while Inmetro used a 0.5 m × 0.5 m open-jet tunnel with an LDA reference and an 8 cm dimensionally calibrated steel disk operating near 7.5 m/s. The results were evaluated using velocity ratios and the normalized error En. For all instruments and all speeds, ∣En∣ < 1, indicating consistency between the two laboratories. The LDA showed the closest agreement, with En near zero in the wind tunnel and about 0.22 when compared to the spinning disk. The Pitot tube reached a maximum ∣En∣ of about 0.44, while the ultrasonic anemometer showed consistently negative En values (from about −0.90 to −0.58), suggesting blockage or installation effects. Typical expanded uncertainties (k = 2) were 0.41–0.45% for the NIST wind-tunnel calibrations, about 0.58–2.0% for the Inmetro Pitot measurements, 0.65–0.85% for the ultrasonic anemometer, and 0.14–0.19% for the spinning-disk LDA. Overall, the agreement between laboratories supports technical compatibility and shows that alignment and blockage effects are the dominant remaining sources of error.

Proceedings Title

The 20th International Flow Measurement Conference FLOMEKO 2026

Conference Dates

May 17-20, 2026

Conference Location

Nara, JP

Conference Title

FLOMEKO 2026

Pub Type

Conferences

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Keywords

Airspeed, bilateral comparison

Citation

Crowley, C. , Shinder, I. , Boyd, J. , Costa, F. and Araújo, S. (2026), Bilateral Airspeed Comparison (2&#8211;20 m/s) Using Three Transfer Standards, The 20th International Flow Measurement Conference FLOMEKO 2026, Nara, JP, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=961466 (Accessed May 28, 2026)

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