Analysis of Noise Generation by Turbulent Jets from Consideration of Their Near Acoustic Field

Abstract

The paper studies the generation of acoustic waves near the boundaries of swirling and nonswirling turbulent jets outside a jet flow. Nonstationary motion of the medium is analyzed. In the case of swirling jets, the occurrence and propagation of perturbations were studied experimentally, while in the case of free turbulent jets, both experimentally and numerically on the basis of LES technology. The results of the study show that, near the jet boundaries, there is a region in which the phase difference between pressure and velocity pulsations at fixed frequencies is 90° or more; i.е., there are no perturbations propagating outward. The phases of velocity and pressure pulsations coincide starting from some significant distance from the jet boundaries. The region in which the phase difference varies from 90° to 0° lies outside the jet flow and is presumably the sound generation region. It is proposed that this region be identified with the near acoustic field of jets.