Azimuthal Structure of Low-Frequency Noise of Installed Jet

Abstract

An experimental study of the azimuthal modes of the sound field generated by a single-stream round jet installed near a flat plate is presented. The investigation is conducted at subsonic Mach numbers (up to 0.82) for the configuration in which the plate trailing edge is located in the linear hydrodynamic jet near field. It is shown that the azimuthal modes of the acoustic field contain additional information compared to the total signals and allow more precise characterization of the installation effect in the low-frequency domain where it is most pronounced. The factors influencing the accuracy of the azimuthal decomposition are considered. It is demonstrated that jet noise remains practically unaffected by the plate and that installation noise is localized in the azimuthal modes antisymmetric with respect to the plate. A novel procedure of splitting total noise into jet noise and installation noise components is proposed. It is shown that this procedure allows more precise determination of the installation noise parameters, which are shown to correspond to the analytical model based on the scattering of the jet near-field pulsations by a half-plane. Correlation properties of the azimuthal modes in the installed and uninstalled configurations are also investigated and analyzed.