Optical Doppler flowmeter for gases

A description is given of a laser flowmeter for measuring the local velocities of steady-state gas flow in large wind tunnels. The flowmeter can be used to measure velocities from 5 to 5000 m/sec and to determine the velocity profiles to within ±250 mm in the horizontal plane and to within ±15 mm in the vertical plane, relative to the selected origin of coordinates. The flowmeter comprises a single-frequency gas laser of the LG-159 type, a Farby–Perot interferometer with a dispersion range of 2000 MHz, and a photoelectric system for recording the Doppler frequency shift. The results of experimental tests of the flowmeter in the velocity range 5–100 m/sec are reported.