Similarity spectral analysis of installed high-performance jet engine noise

Because the noise source mechanisms and radiation properties associated with high-thrust, tactical jet engines are not fully understood, full-scale measurements and analysis can shed significant insight. One method for examining spectral data is to compare them to empirical models for jet noise spectra. This paper compares measured near-field spectra from an installed F-404 engine with analytical similarity spectra for fine-scale mixing noise, large-scale mixing noise, and broadband-shock associated noise. This similarity spectral analysis enables us to determine spatial trends in overall level and peak frequency, and the relative importance of each type of noise radiation per location. This approach can be used to gain insights for different engine conditions as well as quickly compare to other aircraft.