Jet Noise : 1st Report, Far Noise Field of Subsonic Free Air Jet

Abstract

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 contributed to 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 lower frequency side, which is proportional to ω^-4 in higher frequency and to ω² in lower. The acoustic intensity of higher frequency increases proportionally to y₁^-3 in the mixing region and to y₁^-10 in the turbulent region and of lower, to y₁⁺³ and to y₁^-4 respectively, that is, the higher frequency noise is generated mainly near the nozzle exit and the lower, in the transition region.