Noise from commercial high-bypass ratio turbofan engines is generated by turbulent mixing of the hot jet exhaust, fan stream, and ambient air. Serrated aerodynamic devices, known as chevrons, along the trailing edges of a jet engine primary and secondary exhaust nozzle have been shown to reduce jet noise at takeoff and shock-cell noise at cruise conditions. Their optimum shape is a finely tuned...

We present a combined experimental and computational study of the dual-stream exhaust of a supersonic turbofan engine with noise-suppressing deflectors installed in the fan stream. The focus is on validating the computational code, extracting turbulent kinetic energy (TKE) trends, and connecting those trends to the measured noise reduction. We consider two operating conditions, a “cold” conditi...

Prediction of jet noise is important for civil aircraft. Some CAA methodologies predict the full unsteady flow field of a jet in order to ascertain the far-field noise. The approach adopted here is to utilise CFD to obtain steady state information using a turbulence model and hence to provide inputs to a semi-empirical noise model, herein after referred to as the four source model. Predictions ...

An understanding of jet noise source mechanisms can facilitate targeted noise reduction efforts. This understanding has been enhanced with acoustic imaging technologies, such as near-field acoustical holography (NAH). In this study, multisource statistically optimized NAH (M-SONAH) was used to image the sound field near a tethered F-35 aircraft at multiple frequencies. A linear microphone array...

Because jet noise consists of extended, partially correlated sources, a multi-wavepacket model is appropriate to simulate jet noise field levels as well as the appropriate spatial coherence properties within the field. Here, the Hybrid method is used to reconstruct the levels and coherence properties of the source region for multi-wavepacket numerical models. The beamforming source results are ...

We use input-output analysis to examine subsonic and supersonic turbulent jet noise. For a supersonic jet, the leading input-output mode closely resembles wavepackets resulting from the parabolized stability equations (PSE). For a subsonic jet, however, input-output analysis produces several sub-optimal modes with nearly the same gain as the leading input-output mode. The sub-optimal modes depe...

A model of the interaction of the noise from a spreading subsonic jet with a 4 panel assembly is studied numerically in two dimensions. The e ect of forward motion of the jet is accounted for by considering a uniform ow eld superimposed on a mean jet exit pro le. The jet is initially excited by a pulse-like source inserted into the ow eld. The pulse triggers instabilities associated with the in...

Combustion noise from turbofan engines has become important, as the noise from sources like the fan and jet are reduced. An aligned and un-aligned coherence technique has been developed to determine a threshold level for the coherence and thereby help to separate the coherent combustion noise source from other noise sources measured with far-field microphones. This method is compared with a sta...

Experimental results are presented on a method that eliminatesMach waves from the exhaust of supersonic jets and,hence, that removes a strong component of supersonic jet noise. Eliminationis achievedby surrounding the jet with an annular stream at prescribed velocity and temperature so that all turbulent motions become intrinsically subsonic. No mechanical suppressors are used. Implementation o...