Three-Way Spectral Decompositions of High-Performance Military Aircraft Noise

Abstract

High-performance military aircraft noise contains large- and fine-scale turbulent mixing noise and broadband shock-associated noise. A three-way spectral decomposition quantifies the contribution from each noise type in the sound of a tied-down F-35B aircraft on a linear ground-based array spanning 35–152 deg. This large spatial aperture allows for detailed investigation into the spatial variation in broadband shock-associated noise and fine- and large-scale turbulent mixing noise. The spectral models used in the decomposition capture the main features of the measured spectra with three exceptions: 1) that the F-35B engine noise contains multiple spectral peaks in the maximum radiation region, 2) that the nonlinear propagation increases the high-frequency spectral levels, and 3) that the low-frequency levels in the maximum radiation region are less than those predicted by the large-scale similarity spectrum. The F-35B broadband shock-associated noise has the same characteristic shape and variation in peak frequency as overexpanded, laboratory-scale jets. However, the peak level and width exhibit different trends than laboratory-scale broadband shock-associated noise and those recently reported for the F/A-18E aircraft. The strengths and limitations of current models to represent the spatial variation in the spectral content of F-35B noise can guide research efforts to more fully understand the sound radiation.