Level-educed Wavepacket Representation of Noise Radiation from a High-Performance Military Aircraft

An analytical wavepacket-based jet noise model has been applied for the first time to highperformance, military aircraft noise. Ground-based acoustical measurements were made of a tethered high-performance military aircraft with one engine cycling through four engine conditions. The resulting spectra have been decomposed into fine and large-scale similarity spectral components. The spatial distribution of the large-scale similarity spectrum decomposition provides the ability to extract level-based, data-educed wavenumber spectra and an estimation of the convective speed as a function of frequency and engine condition. The data-educed wavenumber spectra are compared with the axial wavenumber amplitude spectra associated with an analytical wavepacket ansatz. A simulated annealing algorithm is employed to minimize the difference between the analytical wavenumber amplitude spectra and the data-educed wavenumber spectra. The frequency-dependent wavepacket shapes obtained from the optimizations follow expected trends as a function of distance of contracting is length as frequency increases but appear to extend for approximately the same number of wavelengths. The level-based, data-educed wavenumber spectra model the Mach wave radiation associated with the large-scale turbulent mixing noise. This wavepacket model is a step towards producing an equivalent source representation of noise from tactical gas turbine engines to guide future noise environment modeling efforts.