Near-Field Acoustic Measurements of a Supersonic Jet with Localized Parallel Injection

Acoustic measurements of a high-speed jet with localized parallel secondary injection are collected in the near field using an axial microphone phased array placed at locations representative of crew exposure during the takeoff of a tactical aircraft from a carrier deck. The injection geometry is selected from prior optimization studies aimed at reducing far-field noise. Tests utilized conditions representative of tactical aircraft engines, with a primary jet speed of [Formula: see text] and a secondary-to-primary mass flow rate ratio of 0.28. The secondary injection reduces the peak A-weighted overall sound pressure level by 5.4 dB. The corresponding pressure skewness decreased by 49%. High-resolution measurements near the region of peak emission were obtained using a scanning sensor. Partial field decomposition of the scanning sensor signal was used to estimate the pressure field along the scan line. Space–time correlations were used to extract the convective Mach number [Formula: see text] along the scan line. It is found that [Formula: see text] is largely independent of frequency and remains fairly constant, at a supersonic value, within the scanned region. Wavenumber–frequency spectra of the leading partial field demonstrate that the injection suppresses the amplitude of supersonically convecting disturbances. These results provide strong evidence that Mach wave emission is attenuated.