Abstract
A wind-tunnel model program was conducted to investigate the effect of aircraft forward speed on the jet noise characteristics of a single subsonic jet. The tests were performed in the United Technologies Research Center Acoustic Research Tunnel, a low-noise open-jet anechoic wind tunnel designed specifically for acoustic testing. Electrically heated air was supplied to a convergent nozzle located on the tunnel centerline. The nozzle diameter of 2.4 in. produced a tunnel to nozzle area ratio of 220. Microphones were located at a radius of 50 nozzle diameters in the anechoic chamber outside the tunnel flow. Nozzle operating conditions covered a range of velocities up to 1670 fps, and temperatures to 900°F. Wind-tunnel speeds ranged from near zero to 350 fps. Measured noise data were corrected for tunnel shear layer refraction and moving medium convection effects, thus simulating the effects on the jet noise sources of relative velocity during an aircraft flyover. Measured overall sound pressure level reductions due to relative velocity were correlated with relative velocity raised to an exponent that increased towards the aft angles. The results showed general agreement with recent National Gas Turbine Establishment (NGTE) test results obtained in a large wind tunnel.
Published Version
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