K.K. Ahuja, J. Manes, K. Massey

The work described here is conducted to quantify and obtain a physical understanding of noise reduction mechanisms in supersonic, single and coaxial rectangular jets, with emphasis on shock noise reduction. The noise characteristics of such nozzles are measured in the GTRI anechoic facility. For all conditions, corresponding acoustic measurements for an equivalent round jet (defined as having the same thrust, mass flow rate, and exit area as the rectangular jet) are also obtained so that the noise characteristics of the two types of jets can be compared directly to quantify the noise reductions. Comparisons have thus been provided for a single rectangular nozzle versus a single equivalent round nozzle, and a coaxial rectangular nozzle versus an equivalent round nozzle. For selected conditions, a comparison of the noise performance of a coaxial rectangular nozzle with an equivalent rectangular nozzle is also provided. It is shown that different operating conditions and nozzle arrangements for the same thrust, total exit area, and mass flow rate can produce different noise levels. With at least one stream operated supersonically, the coaxial rectangular nozzle operated in the invertedvelocity profile is always quieter than in the normal velocity profile mode for the same thrust, exit area, and mass flow rate. In general, the coaxial rectangular nozzle is shown to be quieter than an equivalent circular nozzle only for those conditions for which both nozzles are operated supersonically. Most noise reduction is obtained as soon as the inner jet reaches a Mach number of unity. Even when the primary and the secondary nozzles are operated at the same Mach numbers, the noise produced is less than that produced by an equivalent circular or rectangular nozzle for Mach numbers up to about 1.2. The effect of the base flow resulting from the lip of the primary nozzle could be the attributing factor. It is also shown that both the coaxial rectangular nozzles and the single rectangular nozzles are much quieter in the plane of the major axis than in the plane of the minor axis. It is found that the screech-type tones and broadband hump around the screech tones associated with underexpanded circular supersonic jet noise is almost non-existent for rectangular single and coaxial nozzles in the plane of the major axis. For supersonic equivalent mach numbers, the single rectangular nozzle is quieter than an equivalent circular nozzle and the coaxial rectangular nozzle is quieter than an equivalent rectangular nozzle.

DGLR/AIAA 14th Aeroacoustics Conference, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 9 Seiten

DGLR-Bericht, 1992, 1992-03, DGLR/AIAA 14th Aeroacoustics Conference - Proceedings; S.752-760; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1992