Noise Sources of Closely Installed Subsonic Jets

Abstract

Emitted noise of an installed jet is significantly louder, compared to an isolated jet. When the jet is installed closely under a solid surface, nonlinear jet-surface interactions occur and modify the jet turbulence in addition to the linear potential field interactions. In this paper, the noise sources are decomposed into quadrupole sources due to turbulent mixing and dipole sources due to the unsteady loadings on the surface. The change of the two sources due to the close installation is first characterised in the near-field and their contribution to the far-field noise is then quantified. The quadrupole source and noise are examined using Goldstein’s acoustic analogy, while the dipole noise is studied with the Amiet approach to model trailing edge scattering of evanescent hydrodynamic waves. The methods are first validated in a plate-jet configuration and then applied to analyze the noise sources of a closely installed jet-wing configuration. The results show that the increased quadrupole source primarily contributes to the installation noise at the polar angle of 30 degrees, while the dipole source is responsible for the installation noise at the higher polar angles.