Experimental and Numerical Investigation of Acoustic Source Localization and Forward Flight Effects of a Nozzle to Enhance Jet Noise Shielding Effect

Abstract

This study investigates acoustic source localization and the forward flight effect of a nozzle that can enhance the shielding of jet noise, as proposed in a previous study. A previous study showed that a nozzle exit shape with eight lobe-like triangular teeth provided a higher acoustic benefit for a given 3D long × 3D wide shielding plate than a conical nozzle with the same exit area. Previous numerical analysis also suggests that noise reduction was caused by a change in the sound source distribution owing to the nozzle shape. This study investigated the changes in the sound source distribution by acoustic source localization, and the effect of noise reduction for a jet Mach number of 0.8 was examined under simulated flight conditions using a low-speed wind tunnel. Furthermore, the relationship between the flow field, source distribution, and forward flight effect was elucidated through numerical analysis. Experimental phased-array microphone measurements indicate that the proposed nozzle shape changed the source distribution of jet noise to a position that enhanced the shielding effect. Meanwhile, far-field noise measurements indicate that the proposed nozzle provided acoustic benefits compared to a reference nozzle even under simulated flight conditions. The numerical results showed that the outer free stream weakened the shear layer and changed the magnitude of the turbulence kinetic energy (TKE). However, it maintained the source distribution associated with the TKE distribution created by the nozzle geometry. This supports the experimentally observed relationship between the acoustic changes. These results suggest the possibility of using nozzle geometry to enhance the shielding effect of existing aircraft configurations without using special shielding surfaces.