Noise generation is investigated in subsonic isothermal round jets at Mach numbers M =0.6 and M =0.9, with Reynolds numbers ReD =1700 and ReD 10, using causality methods on data provided by large-eddy simulations. The correlations between broadband sound pressure signals and broadband turbulence signals along the jet axis and the shear layer are calculated. The normalized correlations are found...

Crackle, the impulsive quality sometimes present in supersonic jet noise, has traditionally been defined in terms of the pressure waveform skewness. However, recent work has shown that the pressurewaveform time derivative is a better quantifier of the acoustic shocks believed to be responsible for crackle perception. This paper discusses two definitions of crackle: waveform asymmetry versus sho...

High intensity acoustic radiation occurs when turbulence convects past airframe trailing edges. A mathematical model is developed to predict this acoustic radiation. The model is dependent on the local flow and turbulent statistics above the trailing edge of the flight vehicle airframe. These quantities are dependent on the jet and flight vehicle Mach numbers and jet temperature. A term in the ...

Jet noise consists of extended, partially correlated sources such that a single-wavepacket source representation is inadequate. A multiple-wavepacket (MWP) model provides an analytical framework for jet-noise-like radiation to simulate jet noise field levels as well as the corresponding spatial coherence properties within the field. Here, a beamforming method with regularization is applied to n...

Theories of turbulent time correlations are applied to compute frequency spectra of sound radiated by isotropic turbulence and by turbulent shear ows. The hypothesis that Eulerian time correlations are dominated by the sweeping action of the most energetic scales implies that the frequency spectrum of the sound radiated by isotropic turbulence scales as ! for low frequencies and as ! 4=3 for hi...

We present experimental data towards the development of a low-order model for the jet noise source for predictions of isolated and installed noise. In the proposed scheme, the source is prescribed on a radiator surface defining the boundary between the inner rotational jet flow and the outer linear pressure field. The source consists of wavepacket-type partial fields whose noise emission can be...

We discuss the development of a simplified model for the jet noise source that can be used in practical predictions of installed noise. In the proposed scheme, the source is prescribed on a radiator surface defining the boundary between the inner rotational jet flow and the outer linear pressure field. The source consists of wavepacket-type partial fields whose noise propagation can be computed...

We present an experimental study, comprising acoustic and mean-flow measurements, of several fan-flow deflector configurations in a subscale dual-stream supersonic turbofan nozzle. The deflectors encompassed internal vanes and external wedges. The aim of the study was to investigate trends of high-frequency noise reduction, in the direction of peak emission, versus the distortion of the velocit...