Comparison of Flyover Noise Data From Aircraft at High Subsonic Speeds with Prediction
Comparison of Flyover Noise Data From Aircraft at High Subsonic Speeds with Prediction

Author: J. Boettcher

Publisher:

Published: 1992

Total Pages: 12

ISBN-13:

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Flyover noise measurements are evaluated for four different military jet aircraft types flying at low altitudes. Flight Mach numbers ranged from 0.5 to 0.9. The analysis shows that noise immission is caused by jet mixing and broadband shock associated noise. Based on the experimental results existing noise prediction schemes are extended toward higher subsonic flight Mach numbers. The novel prediction schemes describe the observed acoustic signatures quite accurately. This holds for the overall sound pressure level in dependence of the emission angle, for sound-pressure level time histories and for one-third-octave spectra.

Prediction of Jet Mixing Noise for High Subsonic Flight Speeds
Prediction of Jet Mixing Noise for High Subsonic Flight Speeds

Author: Ulf Michel

Publisher:

Published: 1992

Total Pages: 9

ISBN-13:

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A method for the prediction of single stream jet mixing noise in flight is presented that can be used for flight Mach numbers up to 0.9. The method is similar to the empirical SAE method. However, two important results of the theoretical scaling law of Michalke and Michel are incorporated: (1) the total noise of heated jets is separated into quadrupole and dipole noise components because they are influenced differently by the flight Mach number and, (2) the influence of the stretching of the jet plume in flight on the overall sound pressure and the frequency of the emitted sound is considered. A relative velocity exponent law is used to correlate experimental flyover data. The correlation is based on all available data for combat aircraft with fuselage mounted engines and flight Mach numbers between 0.5 and 0.9. The difference between predictions with this new method and measured overall flyover levels is generally less than two decibels. The spectra are also well predicted.

An Analysis of Aircraft Flyover Noise
An Analysis of Aircraft Flyover Noise

Author: David Q. Walker

Publisher:

Published: 1978

Total Pages: 60

ISBN-13:

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A detailed analysis of a set of Boeing 727 aircraft flyover noise measurements is presented. The flyover data were acquired over a wide range of sideline distances and angles of aircraft elevation with respect to the measurement position. Relationships are derived for excess attenuation due to ground effect and reflection interference as a function of both frequency and angle of aircraft elevation. Angle of elevation is found to be the principal normalizing factor for excess attenuation in the frequency range 50 - 1600 Hz over measurement distances of 800 - 9000 feet. Ground effect, separable from ground reflection interference phenomena in this analysis, was found to be a maximun in the frequency range 125 - 400 Hz and as high as 17 dB at an aircraft elevation angle of 4 deg. Spectral distortion due to reflection interference is found to be important at high angles of elevation but diminishes rapidly at aircraft elevation angles of less than 20 deg. Recommendations are presented on the use of the results of this analysis to guide the development of improved flyover noise prediction techniques.