Coherence-based Acoustic Source Decomposition of Installed GE F404 Engine Noise

Abstract

Understanding the acoustic source characteristics of supersonic jets is vital to accurate noise field modeling and jet noise reduction strategies. This paper uses advanced, coherence- based partial field decomposition methods to characterize the acoustic sources in an installed, supersonic GE F404 engine. Partial field decomposition is accomplished using an equivalent source reconstruction via acoustical holography. Bandwidth is extended through the application of an array phase-unwrapping and interpolating scheme. The optimized-location virtual references method is used, and variations on this method are discussed. Apparent source distributions and source-related partial fields are shown as a function of frequency. Local maxima are observed in holography reconstructions at the nozzle lipline, distinct in frequency and space. It is hypothesized that the first local maximum may relate to noise generated by large-scale turbulence structures around and downstream of the supersonic core tip. Other local maxima are correlated primarily with Mach wave radiation originating from throughout the shear layer and into the region downstream of the potential core tip but before the end of the supersonic core. Source-elucidating decompositions show that the order and behavior of the decomposition lends to the local maxima being related to distinct source mechanisms, while between the local maxima, there is a combination of mechanisms active, which is likely the cause of spatiospectral lobes observed previously with other full-scale, supersonic jets.