Noise Suppression from High-Speed Jet Using Localized Secondary Parallel Injection

This paper presents an experimental parametric study of noise reduction from a high-speed jet using localized, parallel injection of secondary air. The intent is suppression of noise in directions relevant to deck crew exposure during operation of tactical aircraft from aircraft carriers. The secondary stream is operated at a lower speed than the primary jet, reducing the ability of the primary turbulent eddies to emit strong Mach waves. The experiments are performed under conditions realistic to high-performance turbofan engines, with a primary exhaust speed of 870 m/s and a mass flow rate ratio of 0.28 for the secondary injection. The effects of injector exhaust shape, azimuthal aperture, and azimuthal orientation are investigated. A simple factorial design is based on an acoustic figure of merit that considers the sound power level over a sector relevant to crew exposure. The optimal configuration offers a reduction of 3.1 dB in the [Formula: see text]-weighted figure of merit and up to 5.0 dB reduction in the peak [Formula: see text]-weighted overall sound pressure level within the sector considered. The acoustic surveys are complemented by beam forming that shows the spatiospectral distribution of the noise source and its reduction.