Free-Stream Effects on Jet-Installation Noise of a Dual-Stream Engine

Abstract

An investigation of the effects of free-stream on jet-installation noise is performed using a numerical solver based on the lattice-Boltzmann method. In order to simulate a realistic configuration, a high-lift wing comprised by a main element and a deployed flap (MD30P30N) is placed in the vicinity of a dual-stream engine (GE90-94B). The engine operating parameters are used as inputs to generate realistic exhaust flows. Far-field noise spectra from the isolated and installed jets, obtained through the Ffowcs-Williams and Hawkings analogy, are compared for different polar angles. In the absence of free-stream, the results show a low-frequency noise amplification, occurring mainly upstream of the jet axis. This noise increase is due to a dipole source at the flap trailing-edge, where hydrodynamic waves from the jet scatter as sound to the far-field. With free-stream, the wing produces a downward flow, which deflects the jet plume. There is a consequent change on the shear layer turbulence characteristics, which is responsible for altering the far-field spectral shape and directivity pattern of the overall configuration. Through a wavelet decomposition of the near-pressure field, coherent and chaotic fluctuations are splitted. Near-field spectra show the change in amplitude of fluctuations of coherent structures due to free-stream, which are in agreement with the farfield results.