Jet Noise : Far Noise Field of Subsonic Free Air Jet

概要

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It is the purpose of the present investigation to theoretically indicate the relation between the far-noise-field of subsonic-free-air-jet and the flow-field and make clear the characteristics of the acoustic field of jets on the basis of experiment. The noise intensity depends upon the turbulent velocity correlations and its derivative correlations. The noise emitted in the jet-axis direction is mainly attributed to velocity fluctuations parallel to the axis with lower frequency and that radiated in the direction perpendicular to the axis is determined by those perpendicular with higher frequency. The eddy convection effect is to make spectra move towards the low-frequency side, which is proportional to ω^<-4> at the higher frequencies and to ω^<+2> at the lower. The acoustic intensity of the high-frequency noise increases proportionally to y_1^<-3> in the mixing region and to y_1^<-10> in the turbulent region and that of the low-frequency does so to y_1^<+3> and to y_1^<-4> respectively, that is, the high-frequency noise is generated mainly near the nozzle exit and the lower, in the transition region.
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