Supersonic jets emit noise to the outside in form of Mach waves which are long, straight and have about equal angles. Experiments done by Oertel sen. visualized clearly these Mach waves and he publicized moreover that such Mach waves exist also inside the jet. Experimental and theoretical studies in the past did not allow a complete understanding of the phenomenon up to now, wherefore the need ...

The number of jet and rocket noise studies has increased in recent years as researchers have sought to better understand aeroacoustic source and radiation characteristics. Although jet and rocket noise is finite-amplitude in nature, little is known about the existence of shock formation and coalescence close to the source. A numerical experiment is performed to propagate finite-amplitude noise ...

We present a methodology for the computation of flow fields involving complex perforated surfaces in propulsion applications. Of particular interest is the treatment of perforated flaps used as wedge-shaped fan flow deflectors for reducing jet noise of a supersonic turbofan engine. A three-dimensional Reynolds-Averaged Navier-Stokes solver is used to compute the flow field of the external jet p...

Noise generated from technical devices is an increasingly important problem. Jet engines in particular produce sound levels that are not only a nuisance, but may also impair hearing. The noise emitted by such engines is generated by different sources, such as jet exhaust, fans or turbines, and combustion. Increasing restrictions on the allowable noise-emission levels force manufacturers to desi...

This paper describes development of the Jet3D noise prediction method and its application to heated jets with complex three-dimensional flow fields and installation effects. Noise predictions were made for four separate flow bypass ratio five nozzle configurations tested in the NASA Langley Jet Noise Laboratory. These configurations consist of a round core and fan nozzle with and without pylon,...

Conical multiple-jet nozzles, which reduce the risk of nozzle openings being blocked, are tested for their effectiveness in noise reduction. Nozzles with different exit spacings are tested. It is found that the multiple-jet design significantly decreases noise levels in the audible range by shifting emitted sound power to higher and ultrasonic frequencies. No significant difference in noise cha...

One issue of interest pertaining to the development of a numerical model applicable to the nonlinear propagation of jet noise is the behavior of spectral predictions at large distances. In this study, a recorded noise waveform from a military jet aircraft is numerically propagated via a hybrid time-frequency domain solution to the generalized Burgers equation that incorporates spherical spreadi...