Improved Ultrasonic Fuel Mass Flowmeter for Army Aircraft Engine Diagnostics.

摘要

An advanced prototype ultrasonic flowmeter system was designed, fabricated, and tested at fuel flow rates from below 100 lb/hr up to 6000 lb/hr at temperatures from 50 to 115 F and in the Reynolds number range from below 1000 to above 30,000. In order to reduce errors due to flow profile to a small fraction of 1% of full scale, and to avoid the need for a profile-dependent meter constant despite operation over laminar, transitional and turbulent flow regimes, a rectangular flow channel was provided in which the flow was obliquely interrogated over its complete cross section by a square-enveloped ultrasonic beam. The cell included screens for minimizing eddies at the transducer ports, gradual circular to rectangular pipe transitions, flushing means, and a bleed port. Flow related parameters were measured by utilizing a fully coherent electronic system which operated synchronously from a 5-MHz crystal controlled oscillator. The transmitted waveform was generated by means of synchronously gating the output of the 5-MHz oscillator for a 50-microsecond interval at a 2-kHz repetition rate. Upstream and downstream common-path transmissions were consecutive and spaced 250 microseconds apart. Independent measurements were made of the phase difference between the upstream and downstream 5-MHz spectral components of the received waveforms and the phase sum of the 2-kHz modulation components of these waveforms. These two independent measurements were combined to yield the Mach number v/c and v, where v = flow velocity and c = sound speed.