Subsonic installed jet noise scattering prediction using BEM and an optimized wave-packet model

The propulsion-airframe acoustic interaction is an aspect of growing interest in aircraft noise assessment. The development of low-order models for the jet noise source is vital to address the scattering from the surfaces with computational costs compatible with the conceptual or preliminary design phase when complete computational fluid dynamics simulations are not yet affordable for the effort and time required. In this study, we use a jet-noise wave-packet model capable of modelling both the hydrodynamic and acoustic part of the pressure fluctuations. The model parameters are optimized using near- and far-field information from a large eddy simulation of a free subsonic jet at multiple radial distances. The use of near-field data is based on the observation that the scattering surfaces are typically separated from the jet axis in the radial direction only by a few nozzle diameters. The noise source is then implemented in an in-house open-source Boundary Element Method code (AcouSTO), solving the Kirchhoff-Helmholtz equation to evaluate the scattering and propagation of the pressure perturbation in the far field. The BEM simulations show an increased directivity in the upstream direction for the installed jet, in agreement with the observation presented in the literature.