U. Michel, J. Böttcher

Lighthills acoustic analogy is used to describe jet mixing noise in high-speed flight. The two coordinate systems found in the literature for describing the source integrals are discussed, i.e., the coordinate system fixed on the nozzle, used by Rihner and Michalke, and classical coordinate system fixed on the moving eddies, used by Lighthill and Ffowcs Williams. It is shown here that only the use of the coordinate system fixed on the nozzle can explain the frequency shift as well as the forward-arc amplification of jet mixing noise that is observed during high-speed flight. A possible explanation for this discrepancy between predictions made with these two coordinate systems is that the condition of stationary randomness of the source distribution is violated when the classical moving coordinate system is used. The scaling law of Michalke and Michel for flight effects at low Mach number flight speeds, which is based on the coordinate system fixed on the nozzle, is then used to examine factors that have to be considered in any empirical flight effects law for high flight speeds. (i) The total noise of heated jets has to be separated into quadrupole and dipole noise components because they are influenced differently by the flight Mach number. (ii) The influence of the stretching of the jet plume in flight on the overall sound pressure and on the frequency of the emitted sound must be considered. (iii) The frequency observed on the ground is Doppler shifted in accordance with the flight Mach number. A scaling law which satisfies these conditions and which was developed by correlating all available data for combat aircraft with fuselagemounted engines and flight Mach numbers between 0.5 and 0.9 is then used to determine the noise reduction potential through increase of the engine mass flow rate for constant thrust.

DGLR/AIAA 14th Aeroacoustics Conference, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 8 Seiten

DGLR-Bericht, 1992, 1992-03, DGLR/AIAA 14th Aeroacoustics Conference - Proceedings; S.846-853; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1992