An experimental study of subsonic jet noise and comparison with theory

Measurements of the noise field from three 1.52, 2.4 and 2.84 inch diameter subsonic cold-air jets are presented. The tests were conducted in the anechoic chamber of National Gas Turbine Establishment, Pyestock, on a test rig with a very large contraction ratio (maximum 250:1, minimum 70:1) and with an air supply system which has been shown to produce a jet having a low turbulence level just upstream of the nozzle exit and whose noise is dominated by pure jet mixing noise. Comparison of the results is made with the theory by analysing them in detail by determining both the jet velocity dependence and the directivity of the intensity of the radiation in 1/3 octave bands at particular values of the Doppler corrected Strouhal frequency given by ( fD/V J ) (I- M c cosθ ).

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